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There May Be An Evolutionary Reason That You Find Your Brother Gross

There May Be An Evolutionary Reason That You Find Your Brother Gross

By: Allison Tatum, Ashley Rioux, Amoni Young, Carter Smith, Ji’Asia Anderson

Have you ever thought, “Man, my brother is hot!” or “I would date my sister”? No? Well, neither have a lot of people and there may be a reason behind that. 

There are not many cases of people jumping into the bed with family members–but why is that? For a long time, the dominant theory (endorsed by Sigmund Freud and many others) was that cultural taboos prevented people from having sex with close family members. For example, an article by the Royal Anthropological Institute of Great Britain and Ireland, discusses the historical social taboos around incest. This perspective suggests that the reason you don’t find your siblings sexually attractive is that society has created a taboo around incest, and that this keeps our animal instincts toward close family members in check. 

However, let’s take a moment to imagine that we live in a different kind of culture, say, one that celebrates sex between siblings. Imagine that it is expected that when each child becomes an adult, they will select whom among their siblings they will marry, settle down with, and raise a family with. If you lived in such a culture, then would you feel excited about the prospect of having sex with your brother or sister? I mean why wouldn’t you be happy? Don’t you like your brother? Isn’t your sister super cool, and don’t you two have a bunch of shared interests? And you know everything about each other, and you really like each other–seems like a perfect match! 

If you’re still not convinced, you’re not alone. And the fact that this intuition that a sexual relationship with a sibling would just be gross, and not feel right, regardless of what is expected of us culturally or socially, suggests that there might be something beyond taboos that is preventing us from choosing our siblings as mates.

In contradiction to the cultural taboo hypothesis of incest avoidance, other researchers have hypothesized that we may have an innate aversion to incestuous behaviors. 

The Evidence 

One study, published in the journal Nature, found evidence that supports the notion that humans have inherited mechanisms that allow us to detect family members. The participants were instructed to respond to questions to examine family life as well as any interactions with siblings. Results supported the idea that humans have a “kinship estimator” which allows us to know who our siblings are. This study focused on the Westermarck effect to help prove that humans have these different mechanisms to stop inbreeding. 

The Westermarck Effect  

How do we learn who our siblings are? In other words, what “cues” are these innate incest-avoidance mechanisms using to determine who is too closely related to us to be an acceptable mate?

Think about a childhood friend of yours that grew up with you like a sibling. Would you ever date or marry that person? If your answer was “not in a million years”, then you are not alone–and this could give us some insight into how our incest avoidance mechanisms work. 

An article, published in the journal American Anthropologists, found support for a concept called the Westermarck Hypothesis, which states that children who grow up together are more likely to not want to get together sexually when they get older. The researcher in this study examined children who lived together as young kids who ended up getting married when they were older. These kids were NOT related. However, most of the marriages failed, which supports the idea of the Westermarck Hypothesis.

That’s not all that has been demonstrated. A study published in the British Journal of Developmental Psychology, conducted a study to see if there would be a sex difference in inbreeding avoidance with the effect of socialization during early childhood. Participants provided a list of people they knew that they could marry and categorized them based on different outcome variables, like their kindness, how much time they spent together and of course, whether the two were cousins. They found that females would rather not marry someone that they spent time with during their childhood more than males; however, males seem to show an aversion to cousin marriages. 

To add more evidence to the Westermarck hypothesis, as published in the journal Evolution and Human Behavior, there was a study to see if co-residence among siblings does in fact lead to incest aversion. Just brace yourself for this one because this is the point where it gets weird: Researchers had the participants look at different explicit stimuli and asked them to imagine doing these acts with either their partner or older brother. Ew! Though, “ew” is exactly the point that the researchers were trying to make! The fact that there is a disgust response to this kind of study further supports the point that correspondence among children/siblings leads to an “ew” thought about incest. 

So, maybe Westermarck was onto something?


Inclusive Fitness Theory

Okay, we know that there’s evidence that we have a mechanism that allows us to detect siblings, but what does society think about this whole concept?

To address this question, in a review published by Emory University, the author focuses on determining why incest avoidance exists. The purpose of this article is to discuss the possible social and biological mechanisms that correlate with inbreeding in various cultures and its prohibitions. Universally, sex between first order relatives are frowned upon, but sexual relations among cousins and other relatives varies on acceptance among cultures. There is debate on the biological predisposition and social factors of inbreeding among humans. One social factor is the idea the mothers play an important role in the development of incest resistance. The relationship between mother and child after birth has the potential to determine the chance of inbreeding at a later age, particularly between the mother and child or later when the child becomes an adult and has children of their own.

Wait…they’re siblings!?

Furthermore, in an interesting study, published in the Journal of Abnormal Psychology, researchers looked into the mindset of incest offenders by showing them different clips of children (importantly, these clips involved NONSEXUAL activities). The researchers based their hypotheses using the inclusive fitness theory, which states that we have inbreeding mechanisms to stop us from committing sexual acts between those with similar genes as us. Their proposed hypotheses were not able to explain the incestuous behaviors of biological fathers, but their study did show that those sexually interested in extended family members were interested in children more than biological fathers. 

Cue-Based Recognition

A study, published by the Journal of Experimental Child Psychology, performed a test to examine the scent-based mechanism involved in kin-recognition in humans. The participating families were given t-shirts to wear for two days which effectively left their body odor on the shirts. Then, participants were asked to blindly identify the scent of their relatives by smelling the t-shirts. The rates at which they were able to accurately identify familiar scents may provide evidence that scent recognition is an innate mechanism humans use to avoid mating with kin. Furthermore, participants were able to identify their own family’s odor from non-kin families, even in the cases where they were not able to identify the individual family member. This provides evidence for the phenotypic matching mechanism–suggesting that related individuals have similar features that are recognizable by other members of their kin.

Additionally, a review published by the Review of General Psychology discusses cue-based recognition among kin. These mechanisms include familiarity cues, as well as similarity cues. Familiarity cues are based on the idea that an individual will identify kin as those that they grew up with and will find them less attractive as potential mates. Similarity cues are based on scent recognition, and facial recognition. Individuals tend to identify body odors, and facial appearances that are dissimilar to their own more attractive in a potential mate.

I guess you can say we’ve gotten pretty good at detecting our kin over the years.

Inbreeding Depression

Interesting stuff so far, yeah? So, how does this all help us? In other words, why do we have these innate mechanisms to avoid incest–why not mate with our close relatives?

One concept is inbreeding depression, which states that everyone carries 1 to 10 fatal recessive alleles. Ultimately, if you hook up with someone carrying the same fatal recessive allele, the more likely the chance of your offspring surviving decreases. Offspring also have a higher likelihood of having physical/mental birth defects; this does not translate well to creating a successful lineage, meaning one reason incest may be avoided is because of the desire to have a healthy offspring.

The University of Chicago Press published an article which examined the relationship between incest avoidance and survival. This posed the question as to if we as a species, avoid incest due to the complications it can result in when an offspring is conceived. Thus the idea of incest avoidance being a evolutionary survival technique was born. This simply is stating that due to the complications that coincide with incest born children, incest is now avoided to prevent severe health problems in one’s offspring. 

Inbreeding leads to dangerous recessive traits getting passed to offspring

In a review, published by the journal Behavioral Ecology and Sociobiology, there was support found about the dangers of inbreeding depression such as a high occurrence of infant deaths, various types of developmental disorders as well as physical defects.  

So, not so good health wise. However, interestingly enough, there may be some additional cues that we humans look for in terms of knowing who and who not to “get with”:


Psychologists have found that incest is a topic that is met across the board with disgust. The idea of having sexual relations with a sibling is not something many people hope to accomplish or let alone picture in their heads.

However, what if you didn’t grow up with your family member and encountered them years later? What if you didn’t know that they were related to you and you developed feelings for them? How would you proceed with the relationship? The automatic response may be “ew” or “I would know right away,” but that’s not always the case. 

It’s definitely unusual, but is it morally wrong?

One example of how a separation between family at a young age can change the outlook on incest is with Kim and her son Ben. Kim gave her son Ben up for adoption when she was just nineteen year old. Flash forward thirty years later, Ben was on a quest to find his birth parents, and received more than he bargained for. Ben and his biological mother Kim reunited and developed romantic feelings for one another. Ben and Kim are now happily engaged and are trying to grow their family by having a child. 

Now you’re probably thinking “oh my gosh, how could they feel that way? They’re related!” Well, the truth is, most mechanisms that are learned to help distinguish family members from non-family members are a result from spending copious amounts of time with them during childhood. These kinds of cues appear to be much stronger mechanisms than resemblance or scent cues. Therefore, when presented with someone who the other may find attractive, there is no mechanism that is stopping them from having those feelings. Yes, the topic of incest is still frowned upon by society, but can you really blame them for falling for a stranger? 


Lions, Tiger Lillies, Roller Coasters – OH MY!

Lions, Tiger Lillies, Roller Coasters – OH MY!

By Casey Jo Gough, Celine Taylor, & Brice Hinkle

Evolution is the study of change over time. When you hear ‘evolution’ maybe you think of Darwin and natural selection, perhaps you think of apes, perhaps you think of cavemen and hunter-gatherers. Even though the study of evolution draws focus on ancient times, evolution continues to impact the modern humans of today. For example, evolution has equipped humans with biologically prepared fears. Biologically prepared fears are specific situations or stimuli that humans are more likely to fear because this was advantageous for survival or reproduction in ancient humans.

Although stereotypical predators are often the first thought that comes to mind, biologically prepared fears encompass much more than avoidance of hungry beasts. Evolution has supplied the modern human with a plethora of biologically prepared fears unrelated to predator avoidance. Could you imagine anxiety being adaptive? It turns out your friend who’s afraid of roller coasters may be more evolutionally ‘fit’ than you think. And who would have thought a fear of plants might be beneficial? This article will describe a few common fears with unexpected evolutionary origins and explain how these fears functioned in the ancient human as an asset for survival or reproduction. 

Fear of the Ferocious

So what might the ancient humans benefit from avoiding? Lions, tigers, and bears- oh my! Fear of predators protected ancient humans from the dangers of sharp teeth and powerful claws. This adaptive mechanism encouraged humans to behave in a way that would keep them safe and alive, such as hunting in groups and seeking cover come nightfall. This is why poisonous spiders and venomous snakes are among some of the most common fears today. Even though humans now live indoors and have access to extensive modern medical care, our species evolved to avoid anything that would be detrimental to survival. So although the threat of these creatures has lessened in the 21st century, historically humans have benefited from fear and avoidance of this threat, so this fear is likely to continue until it is no longer beneficial. 

Avoidance of predators served as a survival mechanism of ancient humans, but today we live in a world of much less predatorial danger. Although we do not encounter lions and tigers as often as we used to, evolution has still prepared us with some mechanisms for survival, such as anxiety. Anxiety is a specific fear response in humans that entails restlessness, sweating, hypervigilance, and rapid heartbeat. Comparative research of animals such as ground squirrels shows similar anxiety responses to humans. This mechanism in animals results in decreased feeding behavior, decreased exploration behavior, and increased vigilance of surroundings. Therefore anxiety responses in animals are likely related to “detecting and dealing with threats to survival.”

Anxiety is an adaptive mechanism that prepared humans to detect and respond to predators and other dangers. Anxiety allows us to recognize threats by making us hypersensitive to the environment and sensory input but also increases the heart rate to prepare for fight-or-flight. For instance, anxiety is more common in women than in men, possibly because ancient women experienced greater vulnerability to threats. In addition, anxiety is also associated with being alone since humans often traveled and lived in large groups for protection. Without protection from family or mates, the survival of vulnerable women and children may be threatened. These adaptations have evolved into something more commonly known today as stranger anxiety, which would have protected ancient humans from engaging with unfamiliar or threatening rivals. Likewise, the modern fear of public speaking can be traced back to social anxiety, rooted in the evolutionary consequences of reputational failure and ostracism which would result in loss of resources, mate access, and possibly survival. Overall, anxiety is more adaptive than one might think. your sweaty palms and racing thoughts stem from a successful evolutionary mechanism, promoting survival and reproduction. Who knew anxiety was an evolutionary superpower? 

Fear of Falling

Have you ever felt anxiety when being on a rollercoaster? Does your stomach ever feels as if it is dropping? What about even when you are looking over the edge of a mountain lookout, have you ever felt queasy, maybe a sense of panic? This is very common when talking about the fear of heights. Fear, in general, is an adaptive feature that is to protect us; it is natural. This makes the fear of height reasonable as it protected our previous ancestors, which is why we are even here today- they did not fall from very high places leaving them to survive. An excellent study done to show that some fears in general, heights for example, are built-in/adapted and not learned over time is the “visual cliff paradigm,” which has been redone many times since the original. First off, you are probably wondering, “What is the visual cliff paradigm?” It is a test given to infants to see if they have developed depth perception.Image result for visual cliff gif"

Now it is not an actual drop! No babies were harmed in the making of the studies! It is just an apparent (not actual) drop from one surface to another- as seen in the photo below. Glass over the patterned surface is not only over the patterned surface, but the other side as well- glass only, keeping the infant on the same surface type. This is there to lead the child to see the floor pattern seen through glass which makes the infant believe there is/is not a drop depending on depth perception. The deep side and shallow side differ in the way that the pattern is place, the deep side is to show a drop effect.

The visual cliff was done in different ways safely, and to make things sweet and simple, the infants did avoid going across specific setups of a height that showed a dip of elevation. Showing avoidance and not proceeding in something shows a fear, fear of heights in this instance. Yes, the infants continued once they knew it was safe, but they still had anxiety when they crossed because they were unsure of what could happen. There also was an averse feeling to the visual cliff when the infant could start walking compared to when they were only crawling. Overall, the infants did not have a fear of heights because they had fallen, but they did not fall as they had this perceived fear, to begin with. The visual cliff paradigm has been tested with other species such as rats and goats.

What specific features cause this fear, you may ask? Noticing the depth of height, the danger it brings to mind creating the uneasiness/queasy or the panic, what it could do to you fatally. Another specific cause for this is simple; it is for survival reasons, as said before! Nobody wants to fall to their death, so there are precautions that go into place in the mind to avoid this from happening. Next time you are on a rollercoaster and you feel like your stomach is in your throat just know that it is valid!

Going back to the whole phobia ordeal tends to put a damper into saying fear of heights is adaptive. It isn’t necessarily learned. Reasons being that can obtain the fear over time, later in life. People can be screened for this phobia in using the symptom checklist. This being a fear that is gained over time can go back to a person falling, watching someone else fall, or just having an overall negative experience in a high place. However, evolved navigation theory also can prove that the fear of heights comes from adaptation as it talks about the perception of height, which can reduce the likelihood of you falling.  

Fear of Flora

You know how babies like to put anything and everything in their mouths? Well, they don’t like plants. Yes, kids really don’t want to eat their veggies, and they’re not overreacting either. Infants help reveal the biologically prepared fear of plants. Plants contain defense mechanisms such as toxins and spines to prevent predators from eating or damaging them. Studies with infants conducted by Wertz and Wynn reveal interesting behavior exhibited exclusively towards plants.

Infants (between 8- and 18-months) will, more likely than not, avoid touching a plant entirely and look for cues that a plant is safe to touch. In the study, researchers controlled for appearance between a plant, an artificial plant, and a constructed object with plant-like features. A second run of the study was done with shells, everyday household items, and other objects like the previous trial. Wertz and Wynn found that the infants took longer to touch the plant and artificial plant over the object or refrained from contact entirely.  The infants also took longer to touch the plant-like objects over the shells and everyday items. The results of the study point to something about the appearance of plants specifically triggering an alert in the mind of a child.

But Wertz and Wynn weren’t done there. Later that year they examined infants’ (between 6- and 18-months) learning about fruit edibility. Because the infants looked for social cues in the last study, the researchers had good reason to believe that they would pick up information regarding fruit. They ran tests to see how infants distinguished between a fruit’s usefulness and edibility. Experimenters would get the baby’s attention, turn toward a plant with dried fruit and eat the fruit and then to a plant-like creation and move the fruit behind the ear, before placing it back down. All actions in the experiment were balanced for which was done first. Follow-up trials used no cue of edibility, a violation of expectation, and familiar objects instead of creations. Infants were still able to identify plants specifically as edible, but only if a cue to edibility was given, and took longer to eat the fruit if they witnessed the artifact’s fruit is edible.

Wertz and Wynn’s research points to the evolutionarily acquired responses, or lack thereof, to plants and their fruit. Infants do grow out of this though, unless you’re Christina Ricci (sorry, Christina). We are all unconditioned to reasonably fear plants specifically until conditioned to believe plants are safe or learn how to differentiate which ones are and are not. On the bright side, fear of plants is a rarely seen irrational fear that could easily be treated. Most of us like plants now though. Possible future research is already being done to decrypt the nature of how babies learn their way out of this phobia. In a paper published earlier in 2019, Dr. Wynn discussed that infants learn about the properties of plants through observation. The children would look to the adults in the room to see what they thought about the plant, before making contact with it, and often times not making contact when no information was obtained.

Something Beyond Your Worst Fear

Image result for scared of spider stock photo

People have a lot of fears! Whether it’s snakes and spiders, heights or plants, whole milk, or wheat bread, everyone is scared of something. Except for the guy who says he isn’t frightened of anything, but I’m afraid of him. So much work has been done on helping people get over their irrational fears over the past few decades. In fact, Dr. Lars-Göran Öst has found a method of exposure therapy that enables people suffering from specific phobias to move past them in only three hours! It’s ironic that to get over an irrational fear of something you almost never encounter, you will likely have to be exposed to that something far more than you would have ever liked. It sounds scary, but the point of this therapy to show you just how brave you can be. Our phobias developed to keep us safe, not to limit us. Imagine all the little fears we have holding us back, and now imagine if we were all brave enough to act without the restraint of fear. That is real power. Continue reading Lions, Tiger Lillies, Roller Coasters – OH MY!

The “Evil Step-Parent”

Only the Evil Stepmother, or are Stepparents All Evil?

By: Brooke Axelrod, McKenna Hansell, Hayley Mulford, & Sam Paitsel

Step Parents 

     Change is a continual process that happens in everyday life. Some changes can be extremely stress inducing and hard to accept. Unfortunately, a common stressful change that most households undergo is re-marriage. The addition of a new parent can be extremely hard to cope with, as entire family dynamics shift dramatically. Studies have found that the step-parent’s influence can have consequences on children in those families. These consequences aren’t always negative, but could dramatically affect children raised in these step-parent homes during their formative years.

     Many of us have heard the anecdotal phrase “a parent’s love is unconditional”.  However contrary to this, as children many of us were exposed to Disney fairytales, unveiling the evil wrath of the princess’s stepmother. Consistent with these “cartoonish” depictions, research has indicated that a step-parent home can be more dangerous for children: children can be at higher risk of abuse or even homicide by a step-parent compared to a biological parent.

     How can parents be both the benevolent caregiver and the abusive totalitarian? One explanation for this could be genetic relatedness, or the extent to which someone’s genes are similar to your own. In most of the hyper-sensitized Disney depictions, an abusive totalitarian step-mother condemns her step-child while adoring her biological children simultaneously. A perfect example of this is the tale of Cinderella; a young girl’s mother dies and her father remarries, bringing two additional children into the picture with the introduction of a step-mother. Suddenly, Cinderella’s life is dramatically changed as she becomes likened to a handmaiden for these new family members all the while watching her step-sisters be adored by her step-mother. Does this give any weight to the idea that the less genetically related you are to your parents, specifically to your mother, the less parental care you receive? 

Are Step-Parents Depicted This Way for a Reason?

     Evolutionary theorists have suggested that ancestrally, whether or not you were genetically related to a child made a big difference in decisions to invest and care for that child. As we’ll get into shortly, this is because the alternative–investing in all children, regardless of relatedness–would have been a very costly strategy, and therefore selected against strongly by natural selection. This is not to say that people can’t care for unrelated children (clearly they do!), but simply that being unrelated presents one potential barrier to care. Also, it is not an excuse for hostility or abusive behaviors by step-parents (or any parents), but understanding the mechanisms that can sometimes make step-relationships difficult might better enable us to understand the unique difficulties in these relationships and actually help us to promote more positive relationships in blended family households.

    As we just mentioned, evolutionary theorists suggest that cues to relatedness are important in activating parental feelings and motivations toward children. This is because ancestral men and women had to deploy their limited time and resources carefully, in a way that maximized their own genetic interests.  Our ancestors had the obscure problem of ensuring that they were investing in their own child and that their offspring would make it to reproductive age. Since this investment was at a large cost, they would not want to put this into the offspring that do not have the propensity to carry on their genetic makeup. This cost is different for males and females; while females are investing care and time, males are investing resources and the losing the possibility of producing more genetic offspring. This is not to say that a step-father cares more for their step-children, but rather that a step-mother has greater shoes to fill for those children.

    Now, we live in a world that is starkly different in many ways from that ancestral environment, but we still possess these adaptations that shaped our ancestors. By recognizing these adaptations, we are better able to account for their effect. To counteract the sex difference in step-parent relationships, we suggest that bonding with the children is integral. Recognizing these adaptations doesn’t mean we are beholden to them, but rather gives us the opportunity to break free of them. 

  So, Is One Step-Parent Really Worse Than The Other

      The word stepparent conjures up a different image in everyone’s heads, but we all typically envision the same story: evil woman marries the rich widower dad, the dad disappears due to work related things and leaves his biological child behind with the new stepmother, the stepmother then begins to treat the step-child terribly while treating her own biological children well. But is there any truth behind the negative stigma of the “wicked stepmother”? One theory that arises from evolutionary psychology in an attempt to explain this is the mother-child bond, which is believed to be the “intrinsic biological ownness” that mothers share with their children. The logic following this is that biological mothers have a very direct set of “cues” to their relatedness with their children–they carry the children, go through labor, and nurse them. These reliable cues to relatedness are strong triggers of maternal feelings. Without these cues, mothers to unrelated children, like step-children, may have a harder time forming this emotional bond with their children. This sets the scene for step-mothers to experience more difficulty bonding with their step-children, or developing parental feelings toward them. Indeed, evidence suggests that step-mothers are about half as likely as step-fathers to experience parental feelings toward their step-children.

    An additional difficulty step-mothers encounter pertains to gender roles, in which stepmothers “would have to be nurturing, caregivers, and kinkeepers, monitoring the well-being of all family members and their relationship.” These roles are much more difficult to fill, especially considering the already strained nature of stepmother-stepchild relationships. The step-mother has to work harder towards a relationship with the child to strengthen the feeling of closeness, we use today as our cue towards familial bond. This is not to say that these bonds are impossible to create, as they can be created through purposeful involvement by the step-parent towards the child.

     Now that we’ve discussed step-mothers at length, what about step-fathers? Step-fathers are also predicted to have difficulties to overcome in their relationships, albeit for slightly different reasons. Ancestral men–unlike ancestral women–did not possess the same certainty, on average, that a particular child was actually related to them. Because fertilization happens within females, and thus paternity is never certain for males, ancestral men developed adaptations that promoted bonding based on more indirect cues to paternity, like physical and behavioral resemblance. The use of more indirect cues may help to explain the finding we referenced earlier, indicating that step-fathers are more likely to develop parental feelings toward their step-children. Similarly, one study found that children felt their family function was better with a step-father rather than a step-mother. The children felt more communication and co-living with a step-father than with a step-mother. The step-mother has much more relationship to build because of the cues that promote maternal bonding.  Therefore, it can be easier for motivated step-fathers to transition into their new roles with step-children. Step-fathers’ use of more indirect cues suggests that purposefully cultivating a relationship can be accomplished through spending time together engaged in activities of shared interest between parents and children, and finding points of similarity.

Does culture matter? 

    Is this stigma of being an “evil” step-parent attributed universally, or is this localized to only western culture? Most of the research conducted on this subject mainly focuses on families in western culture. Family dynamics are significantly different in western and eastern culture. Families in western cultures tend to be more individualistic and this may play a role in some of the results found. However in eastern communities family dynamics tend to be more collectivist. It would be interesting to see if eastern families who have a step-parent present would yield the same results. Researchers could also look into homes where neither biological parent is present (adoption), and see how they compare to families with either a step-parent present, or both biological parents present. Something else that could be taken into account is the dynamic between half-siblings and their opposing step-parent.

Making Blended Families Successful

     As we said before, the fact that these difficulties have evolutionary roots doesn’t constitute an excuse for abuse, and it also doesn’t mean that all step-relationships are “doomed.”  There are ways to consciously work on building a stronger relationship, and some of these follow predictably from evolutionary theory, like seeking out points of similarity between step-parents and children–especially in the case of step-fathers. One study found that socialization with the child is the most important because it allows them to adopt and share moral values. Another found that the most important parts of step relationships are positive regard for the step-parent, authority accepted by the step-child from the step-parent, and certainty that the child feels they have a relationship with their step-parent. These three things are crucial to build a positive relationship with the step-parent, and can be cultivated through intentional work

Another lesson we can take away from evolutionary perspective on this issue is that those involved in step-mother relationships should be patient with themselves if the relationship does not form naturally or easily. There can be additional barriers in this relationship that may take more time to build, but that doesn’t mean that the relationship will never be built. The theories simply suggest it requires more conscious effort.

    Additionally, there may be some unique perks to growing up in blended families. Interestingly, a study found that children in step family homes actually have better social competence and that there is definitely not a difference between types of families. Social competence enables children to interact and bond with other children better, which is definitely an advantage in the tumultuous terrain of middle school. Thus, there can be really positive outcomes for these kind of families and the children who are raised within them. 

Sadly Cinderella’s relationship with her stepmother is the stereotype everyone thinks of regarding step-mothers. However, this is not the right picture to paint. Step-parents can be very involved, supportive, and real family when the effort and relationships are there.



Has the Brain Adapted to Drugs?

Has the Brain Adapted to Drugs?

by Fenna Andriessen, Sophie Bacon, Dionne Liberia, Stine Løven, and Alyssa Mattson

Drugs have become so ingrained in our culture we have almost become numb to their existence. Celebrities like Miley Cyrus and Snoop Dogg sell hit songs about dancing on Molly and it’s no secret that college campuses have become a space where individuals have the opportunity to experiment with recreational drugs and alcohol.

Our ancestors used to seek drugs for survival purposes. However, now it seems we use drugs primarily for recreational use. Unfortunately, some individuals eventually become dependant on drugs, as exemplified by events such as the 1980s crack cocaine epidemic and the current U.S. opioid crisis.

With that said, there are a few questions that we would like to address. How does context play a role in drug usage? What evolutionary mechanisms have humans developed that lead us to seek out drugs? How does substance use progress to addiction?

Let’s talk about drugs!

Why do we use drugs?

Throughout our lives, we engage in behaviors to seek pleasure, such as food or sex. Because behaviors like these were beneficial to our ancestors’ survival and reproduction, natural selection made them rewarding, or pleasurable, so that we continue to perform them.  Our natural rewards system (mesolimbic dopamine system; MDS) is responsible for these pleasurable feelings. For example, if you are eating a cookie, you are ingesting a tasty, calorie-dense food — something that our ancestors, in their food-scarce habitat, would have considered highly pleasurable and valuable to survival. In our modern-day environment, the feelings of pleasure associated with food and other stimuli remain regardless of their original evolutionary intent or the disadvantages they may now present. As it turns out, many drugs activate this same brain system, stimulating dopamine release and thus, causing a pleasant feeling that we want to experience repeatedly–despite the fact that the drug itself may not be increasing our ability to survive and reproduce. When we use a drug, even with the understanding that it may harm us, there is a risk that this behavior can become an addiction due to the false sense of benefit.

There are two theories that attempt to explain drug use in humans – the hijacking hypothesis and the neurotoxin regulation hypothesis. First, the hijacking hypothesis claims that our drug use is a by-product of the MDS. Drugs would “hijack”, or stimulate the MDS artificially, triggering similar pleasant feelings in users. Despite the widespread acceptance of this theory among researchers, there are several issues concerning its accuracy. Evidence supporting the hijacking hypothesis doesn’t show the whole truth. As the famous rat park experiment findings undermine the claim that drugs hijack decision-making machinery because rats chose the alternative option (sweetened water) instead of the drug. So, it appears as we would choose the cookie over cocaine. Additionally, supporters of the hypothesis claim that our ancestors could not have been exposed to drugs as we currently know them because our drug use is only a byproduct and not an adaptation. They claim that drugs are novel and nowadays we are exposed to them a lot more.

A competing explanation, the neurotoxin regulation hypothesis paints a somewhat different picture. This theory suggests that our ancestors may have used certain drugs to treat illness. Many plants–including those from which many common drugs are derived–have mechanisms designed to discourage consumption (e.g., by insects). For instance, when thinking about tobacco, certain symptoms such as the bitter taste, nausea, vomiting, and diarrhea can occur resulting in someone not wanting to use it again. According to the neurotoxin regulation hypothesis, humans may have evolved to use these drugs to their advantage. Tobacco, for example, is effective against certain parasites that were vastly present in our ancestor’s environment. Thus, in contrast to the hijacking hypothesis, which suggests that drugs are rewarding more or less by accident, the neurotoxin regulation hypothesis claims that drug use is rewarding because it helped our ancestors to reduce the threat of disease. 

One study conducted at Claremont Graduate University in 2003 compared the acute lethal toxicity of many commonly abused drugs. In their findings, it was concluded that an average dose of a drug, while very small, is only slightly below what would be a lethal dose. For the hijack hypothesis to be true, we would expect the MDS system to reinforce large intakes of these drugs – however, humans appear to be capable of monitoring their intake of drugs, thus their consumption of neurotoxins. The neurotoxin regulation hypothesis explains human drug use despite cues to toxicity and how most humans successfully measure intake and avoid an overdose. An additional study suggests that the historical consumption of certain plant neurotoxins provided ancestral humans with benefits including improved cognitive ability, neurological functions and other fitness benefits.

In addition, H. Ahmed and G. F. Koob conducted a similar study in October of 1998 investigating whether short-term and  long-term access had an influence on rats’ ability to self-administer the drug. The study showed that long-term access rats self-administered more cocaine compared to the short-term access rats. It suggests that escalated cocaine use (long-term access) resulted from a change in the hedonic set-point–a higher baseline for when they experience an effect from the drugs. Results found that rats that were given shorter access to cocaine displayed an ability to limit use, suggesting that drugs do not “hijack” the brain, but rather that animals have the capability to regulate use to prevent undesirable fitness outcomes. This study supports the neurotoxin regulation hypothesis in which humans have evolved to regulate and optimize benefits from drugs.


Explaining drug addiction

By examining drug addiction from an evolutionary perspective, we can gain some insight into why these psychological mechanisms occur and how to approach designing treatment programs. Given this perspective, drug addiction is best understood by examining internal influences, including our biology and psychological mechanisms, as well as external influences, such as social and familial factors in our modern environment.

In a historical context, primitive humans sought drugs for cultural ceremonies, religious purposes, medicinal use, and during times of food and resource scarcity given their perceived fitness benefits. However, given the toxicity of these substances, there were serious side effects associated with their use. As they are designed to deter consumption, plant neurotoxins (drugs), may induce headache, nausea and vomiting, diarrhea, and, in extreme cases, erratic or violent behavior, severe physical and mental health problems, and even death. However, in the modern-day, human manufacturing and refinement of these drugs have reduced the immediate severity of side effects while increasing their strength.

For example, cocaine is typically ingested today in a very pure and refined form. Traditionally, however, it was ingested by chewing on a coca leaf. Not only would the concentration of cocaine have been much lower in this form (making overdose less likely), but people would have been ingesting it along with a number of other toxins produced by the plant which would have produced aversive physical symptoms (making overconsumption and abuse less likely). Thus, the neurotoxin regulation hypothesis could explain how our ancestors would have regulated intake and avoided an overdose, and help us understand why addiction, abuse, and overdose are more common today.

In addition to content, research proposes a link between the intense growth of human brains and the utilization of psychotropic plants. Evidence for this notion stems from the belief that in the past, ancient civilizations viewed psychotropic plants as food sources when resources were low. The use of these drugs began to signal false signs of increased fitness and happiness, resulting in the adaptation that perpetuates human drug use.

Looking at drug addiction from an evolutionary perspective allows us to understand the mechanisms that we have adapted for drug use and develop more effective rehabilitative strategies.


We wish we could explain drug use and addiction to you but we don’t have a clear answer–however, the neurotoxin regulation theory has stronger evidence compared to the hijacking hypothesis. In terms of future research, it would be interesting to look at the self-administration of drugs as well as the histories of addicted individuals in order to account for different contexts of drug use.

With that said, it’s important to take into consideration the learning process associated with drug-use and evolution in general. This includes the fact that contrary to popular beliefs regarding evolution, adaptations aren’t set in stone. We aren’t helpless and we can still make a conscious decision to say no to drugs.

We can all agree that our environment has changed drastically, as drugs are all around us–at the pharmacy, on the streets, at parties, you name it, it’s hard to ignore. It’s safe to say that using drugs now isn’t about “survival” it’s more about being cool and fitting in. With all of this said, now you know doing a line in the bathroom is very different from chewing on a coca leaf in the jungle.

Have Men Evolved to Detect and Respond to Cues of Ovulation?

By Sarah Raines, Ryan Casey, Tori Blair, and Chasity Ramsey

Fellas, have you noticed that you find your girl to be more attractive at certain times in comparison to other times? Ladies, do you occasionally find that your man seems to be overly drawn to you more than usual?  If you answered “yes” to one of the questions above, you aren’t alone. It might surprise you to learn that this “yes” speaks to research supporting the hypothesis that men have evolved the ability to detect and respond to different cues of ovulation

                                                         Ovulation and Evolution

Ovulation occurs when an egg is fully matured and released from the ovaries to be fertilized by sperm. This normally happens once per month, about midway between your last and next period, and it is only in the days surrounding this event that it is possible to get pregnant.

Ladies, how many of you know for certain when you’re ovulating? If you’re like many women, you may not be sure. So, if you don’t know when you’re ovulating, how could ovulation possibly impact your behavior, or your partner’s perception of you? As it turns out, neither women nor men need to know when someone is ovulating in order for ovulation to matter. There is a possibility that you do not know when you are ovulating because you do not notice when your body is going through its hormonal changes, but it is, and those fluctuations have noticeable effects–if you know where to look.

Unlike humans, some female animals show obvious signs when they are in “heat” and ready to look for a sexual partner. This is known as Estrus or Oestrus. Sheep, lions, dogs, baboons, and other animals all show signs of being in heat when they are ready to mate. Some of these animals’ butts turn red when they are in “heat” and that lets other animals know that

they are “ready for action”.  Not all animals have pair-bonding between mates so they encourage male conflicts and competitions to determine who they will mate with.

So, why don’t humans have these more obvious signs of fertility? One possibility is that it’s due to the highly social nature of our species. Concealed ovulation in humans has opened the door for stronger pair-bonding. For instance, in some species, males and females only affiliate with each other when it’s time to mate–the rest of the time, they do their own thing. But in other species, like ours, male-female bonds are longer-lasting. Concealed ovulation might promote these longer bonds because neither partner “knows” when sex will lead to a fertilization, and so they have sex across the cycle. Stronger pair-bonding would increase male investment and it could also increase male-male cooperation. It also helps prevent men from fighting with one another for women in estrus. (Besides, I am sure you ladies wouldn’t want to walk around with bright red butts to attract men, would you?)

There have been researchers who hypothesized that ovulation was concealed in humans because it helps women and men form long-term relationships that would reduce men’s chances of looking for another mate. This would have benefits for both men and women: women would receive more investment from men to help care for their children, and it would also cause men to have higher confidence levels of paternity, because they would be with their female partners across the cycle–which leads into our next question.






Why would men need to detect cues to ovulation?

Ancestral men who could identify and attract women who were high in fertility gained more reproductive success over men who were unable to detect fertility. So not knowing when females are ovulating may have decreased the likelihood of our male ancestors of having offspring because they couldn’t respond to females obvious oestrus cues that signal when women are most fertile. This suggests that there would have been an advantage for men who could detect subtle cues that women were ovulating. In other words, if the subtle shifts that women go through during ovulation caused some men to find then more sexually attractive, these men would have been more likely to father children, and would have passed the genes for these preferences on to modern humans. 


What are the subtle cues to ovulation in humans? 

Clothing Choices

Ladies, imagine you are going out for a night on the town and you need to get dressed. What are you mostly likely to choose right now? Shorts and a low cut shirt or skinny jeans with a nice shirt? Maybe a short dress with some high heels or a long flowy sun dress? According to some research, your answer might depend on whether you’re ovulating.  According to Kristina Durante’s study on sexual cues during ovulation, women who are ovulating are much more likely to choose shorts and a low cut shirt or a short dress with high heels than the more conservative clothing.

We also see that both men and women are able to notice this shift. In an evaluation done using pictures of women, 94% of women and 86% of men correctly chose the woman who was closer to ovulating; under the only criteria of, who looks more attractive? This subtle “cue” can show men that you are sexually available, mature or just have a simple ability to reproduce.

Facial Changes

Another study that discusses attractiveness is from Roberts et al. and it states that women’s facial attractiveness may vary and change over the course of their ovulation cycle. The article suggests that the visible cues to human female ovulation are primarily in the face and that this paired with other topics discussed in this post will pair nicely to make our cycles less cryptic or hidden. The results of their study showed that facial attractiveness does vary throughout the ovulation cycle and it can be seen by both men and women. The changes to the face that can be seen, are often clearer skin or a subtle redness to the face, often called a blush.

Image from Roberts et, al.

When looking at the picture to the right, which do you find to be more attractive? If you chose the two left versions then you picked the two that are ovulating. The change that is seen in the pictures are subtle and caused the effect to be minimal. Although, according to researchers, with other “cues,” changes in the face may be significant enough to show ovulation. Note that such possible attractive facial cue features are dilation of the pupils, both the size and color of lips, and skin color and tone. 

Though both of the above studies suggest visual cues to female ovulation, there are other subtler cues, such as smells and voice changes, that suggest ovulation.

Vocal Attractiveness

There are some existing studies on the singing voice changing throughout the ovulation cycle, but in the study discussed here the researchers carried out a review of six different English studies on the same subject and came to the conclusion that because of hormone changes during ovulation, the voice can vary in volume and pitch, which does cause a slight voice change throughout the ovulation process.

 A study that tested if women’s voices changed found that men prefer higher pitched voices rather than lower pitched voices. They also found that when women are ovulating, they speak with a higher pitched tone. This cue to ovulation has been shown in few studies, but it does show that men can hear a difference in pitch and that that difference can make a woman more attractive.

The Scent of a Woman

Smell is a strong sense. It is said smells are the fastest way to transport us back to memories. But can we as humans smell ovulation? If you aren’t convinced that behaviors are different when ovulating, there is even more evidence ovulating woman actually smell different to men than non-ovulating women–and furthermore, there’s evidence that this detection influences testosterone levels.  Testosterone can cause many changes in males, whether there is a large increase or a small one there can be many differences. Innately, the testosterone levels in a man can increase when doing nothing but smelling women’s shirts. Seems strange, but true, and there is more! Not only did the testosterone levels increase when sniffing shirts worn during ovulation, but decreased when sniffing the shirts worn by non-ovulating women.

So why is this increase in testosterone beneficial? Increasing testosterone in males has been linked to an increase in sex drive and overall desire. Therefore, an increase in testosterone when smelling a shirt is a great cue to the innate changes that occur in men when a woman ovulates. This is yet more evidence that evolution is pointing men in ways where ovulation can be pinpointed.

Pretty cool evidence, no? But there are other ways that future research endeavors can provide evidence for men having evolved to detect and respond to cues of ovulation.


Okay, so here’s what we covered!

  • Women’s dress, facial appearance, perhaps voice pitch, and smell seem to serve as cues of ovulation for men.
  • Fluctuations in testosterone as a result of smell seem to be indicators of men’s ability to detect of ovulation.
  • Evolving to pick up on these proposed ovulatory cues increased our male ancestors’ likelihood of having offspring and, therefore, they past those abilities onto us.

And now that we’ve got that covered, here’s what future research can do to add to the body of evidence behind men evolving to detect ovulation.

What’s next? Future Research Directions for Ovulation

Since women express a preference for clothing that will draw more attention or is less conservative, researchers could have women come in at ovulating and non-ovulating times to try on an assortment of more or less conservative outfits.  This would strengthen research because women trying on outfits would mean that their final choice in outfits would most likely result in how the outfits make them feel at low and high fertility times. 

Expanding on the above,  it speaks to the second study mentioned in which participants reported on how much the women cared about being perceived attractively. Researchers could compare the reports on how the outfits make women feel to the ratings done by those indicating how attractive the women want to appear.

Reflecting back to the study in which participants noted the change in women’s faces at ovulating and non-ovulating times, in order to strengthen these findings, it would be good if future researchers had women come in to have photographs taken over the course of several ovulating and non-ovulating times and be able to expose the judging participants to several versus two pictures of women.       

Now, for the changes in voice pitch that women seem to undergo at ovulation, the best case for strengthening the evidence here is for researchers to look for voice pitch changes and men’s attraction to it in multiple contexts. Findings from multiple contexts would be good because a smaller likelihood of factors potentially characteristic of just a few contexts would be affecting the overall body of evidence.

And the same is probably true for strengthening the evidence behind men picking up smell as a sign of ovulation. In other words, why not have men smell women’s jeans, bras, or even hair accessories such as headbands? 

And what about a study that represents ovulation cues being detected over time? Researchers could administer weekly email questionnaires to men to report on attraction to their wives/cohabitating partners. The types of questions asked of participants would inevitably relate to actions/behaviors (e.g. choice in dress and so forth) and voice and smell. 

Well, that’s all folks!

Bet you’ll never look at an attractively dressed woman quite the same as you once did before.


It’s Evo-Lit-ionary: Why Humans Like Drinking Alcohol

By: Luke Harbison, Maddie McCall, Nicole Moughrabi, and Adora Nguyen

It’s no secret that many (if not most) people like to drink — fruity wine coolers, a cold beer, some mixed concoctions that are most definitely shaken, not stirred. But, why? Especially considering that alcohol itself is bitter, toxic, and leads to us being vulnerable and making poor decisions, there must be some scientific reasons other than having fun while losing inhibitions.

And there are — alcohol has been utilized as a medicinal tool, a way to find pleasure and feel good, and as it turns out, our widespread preference for alcohol may even be a byproduct of an evolved adaptation.

But before we get too much into evolution, let’s take a quick look into how alcohol has been used in more recent times.

Medicinal Alcohol


One interesting historical use of alcohol was medicinal. For instance, in Ancient Egypt wines and beers were often used as forms of medicines that could help with a wide-range of ailments: a beer mixed with coriander, bryony, flax, and dates could ease stomach problems; coriander mixed with fruit and beer could help with blood in someone’s stool; salves for herpes were created from coriander, seeds, myrrh, and fermented honey. Alcoholic ingredients were also used as laxatives, emollients (which are soothing lotions for your skin),  and even  aphrodisiacs. In short, alcohol was a key ingredient in healing during ancient times.

But, most of us aren’t living in ancient Egypt, and we can just run to the closest pharmacy to pick up our (much more effective) meds instead of making them ourselves. Why do we still continue to drink alcohol?


One explanation is that we’ve evolved to like the feeling of being drunk (or at least tipsy, for those who might only indulge in a glass of wine once a week). One clue that this might be the case is that alcohol stimulates reward circuits in our brains. When we consume alcoholic drinks there are many chemical reactions happening, namely the release of dopamine, which helps us to feel good. This release of dopamine happens in the nucleus accumbens, which is just a fancy name for the reward center of our brains. In short, alcohol can help us feel good. It helps us relax, offers us a way to connect with others in social settings, and can enhance the food we’re eating. But why does it make us feel good?

Some researchers have argued that the hedonic (or pleasurable) qualities of a stimulus (like food, or water when you’re really thirsty, or sex) are indicators of its “fitness goodness,” or in other words, whether something will help us survive or pass on our genes. Animals who found pleasure in “fitness good” stimuli were therefore more fit than those who didn’t (evolutionary speaking, meaning better able to survive, reproduce, and pass on their genes — not necessarily able to lift weights). This means that animals that sought out those pleasure-rewarding stimuli were overall more successful than those who didn’t. So, the fact that alcohol feels good to us suggests that alcohol–or something associated with alcohol–might have actually been good for our ancestors’ fitness.

Before we get to what that “something good” might be, though, it’s important to point out that this reward mechanism can go awry, which in the case of alcohol and other dopamine-stimulating drugs, it certainly can. There are some studies that state alcoholism can be considered an “evolutionary hangover” of this reward mechanism. Over time, humans have become very skilled at seeking out pleasurable stimuli over more important or necessary things, such as food or water, which is a not-so-good thing.

The Genetics of Alcoholism 

There are multiple studies that put forth the argument that certain genes were evolved to help with the breakdown of ethanol and metabolize alcohol–another clue that alcohol is a part of our evolutionary past in some way.


However, consuming too much of ethanol can have great risk, considering that these specific genes can also influence a person’s risk of becoming an alcoholic. Various alleles (or versions) of these genes may determine the likelihood of someone developing alcoholism based on how they break down ethanol. In short, two people could drink the same amount over a span of a few weeks, but the person whose genes are more inclined to addictive behaviors and efficient breaking down of alcohol runs the higher risk of becoming addicted. It is likely, based on these and other studies, that these genetic risks are at least in part explained by how rewarding people with different gene variants find the consumption of alcohol.

Risk Taking Behavior

Furthermore, other studies have shown that an important behavioral predictor of alcoholism is tied to one’s levels of impulsivity; the more impulsive someone is, the greater chance of excessive consumption of alcohol and, ultimately, alcoholism. Impulsive behaviors may arise from genetic properties or can be influenced by social factors. Thus, alcoholism is not thought to be caused by one element, but rather a combination of various genetic, behavioral, and learned traits (it’s nature AND nurture — no “vs” here).


We humans also have a tendency to start drinking at a young age, possibly even younger than certain laws may allow for. This may be due to alcohol being a (literal) forbidden fruit; some studies have shown that adolescence is the time in which behavior prohibited by authority seems enticing (i.e. underage drinking). Adolescents see themselves as being invincible and unafraid of the unknown, which prompts them to actually seek out certain ambiguities — such as underage drinking.

As you can easily guess, underage drinking is not really a good thing to do; not only is it illegal in some societies, but it can also hinder brain development, considering the brain isn’t fully developed until you’re almost 30. So while drinking alcohol can make us feel good, there are very real dangers that come with drinking.                                                                                                                                                                     

Which brings us, finally, to what evolutionary psychologists consider the underlying cause as to why humans like drinking alcohol: for our ancestors, it all came down to food.

Ripe Fruit and Digestive Fermenting

A major challenge our ancestors faced was obtaining enough food, and food that wouldn’t be dangerous to us. A solution to this problem was to evolve taste preferences that helped us determine which foods offered the most calories and aversions for things that were toxic. For example, humans tend to enjoy rich umami tastes, which are associated with foods rich in fats and proteins, such as meats. In contrast, we tend to avoid very bitter tastes, as bitter foods tend to contain compounds that are toxic to us.

We also like sweet tastes, which are associated with high-sugar foods, such as sodas and cakes in modern times. This sweetness preference is why our ancestors feasted on delicious, ripe fruit (the closest thing to cake that they had available)… which also just happened to have high levels of ethanol. This also answers the question as to why we enjoy a drink that can be so bitter. Because it wasn’t always so bitter — it used to be sweet and fruity.

This main hypotheses that explains why we enjoy alcohol is called the Drunken Monkey Hypothesis. By studying monkeys, who are our closest evolutionary relative, we find that their diet is predominately plant-based; this supports multiple pieces of evidence that our ancestors also ate many plants. But while monkeys often times seek out ridiculously ripened fruit because of their high level of calories, those fruit also have high levels of ethanol (reaching 1%), which then ferments while digesting, and ends with the monkeys becoming drunk. This can also happen to any animal that eats the fruit, and below is a video of a bunch of animals who hopefully have their own DD.



But notice that the animals go after the fruit because they are ripe and have high levels of calories — becoming drunk only happens coincidentally. This is called a by-product, or a secondary characteristic that gets carried along by an adaptation, which is the actual evolved solution to a survival or fitness problem. So in this case, our ancestors faced the problem of selecting the very best fruits to eat, evolved a preference for sweetness that solved this problem, and coincidentally, also developed a taste for the ethanol that was also in the ripe fruit.

Take Aways

There are many reasons as to why modern-day humans enjoy drinking alcohol, and if you ask anyone you’re almost guaranteed a few of those answers. However, alcohol has been used for more than just drinking. Just to recap:

Alcohol was once used in ancient medicines that would solve an assortment of ailments (although, today the main ailment solved by alcohol is social anxiety or a stressful job).

But as far as researchers can tell, the deeper evolutionary reason as to why we drink is because our ancestors feasted on ripe fruit whenever they could get it, and their taste for fruit carried on to us. Our drunk cousins, the monkeys, can demonstrate this with their penchant for alcoholic fruity drinks.

Which can unfortunately lead to large amounts of consumption, potentially resulting in alcoholism. Different genes and chemicals are used to breakdown alcohol, but these genes and chemicals can also determine whether or not someone is more likely to become an alcoholic.

When it comes to drinking alcohol, no matter the reason why or how, it is important to be safe and be smart. Remember, it’s survival of the fittest — not the survival of the drunkest!


Jealousy: Successful Tactic or Harmful Emotion?

By North Angle, Cristoni Couvrette, and Anne Mette Rasmussen

Imagine you’re sitting at home scrolling through some sort of social media platform (whether it’s Facebook, Instagram or snapchat) and you see that your significant other has been commenting (or posting) flirtatiously with his/her hot coworker. How do you feel? Most people would immediately feel a sense of possession overcome them when they see their partner’s attention focused intently on someone else. Jealousy is an extremely strong — and surprisingly old, in an evolutionary sense — emotion.

Even though modern attitudes about relationships have become significantly more flexible, jealousy is still a common part of our love lives. Whether people are swingers, friends with benefits or serial daters, jealousy is commonly found. This powerful emotion can inspire songs, strengthen a relationship or even prevent a relationship from ending. However, the same emotion has the power to cause a breakup, inspire hatred, or result in serious harm.

But why do we get jealous? In this post we’ll explore this question from the perspective of evolutionary psychology. We’ll explore the adaptive benefits of expressing jealousy, the gender differences in jealousy, and lastly the benefits and setbacks that jealousy gives romantic relationships today.

Why do we get jealous?

Jealousy for many people is recognized as an undesired emotion that can trigger unflattering and unwanted thoughts and behaviors. Although unpleasant, evolutionary psychologists hypothesize that jealousy has been a beneficial solution to the problems that our ancestors faced. More specifically, jealousy is hypothesized to be a solution to mate retention. Ancestral men and women needed to retain their mates in order to reproduce successfully.

Mate retention can be threatened in various ways, for instance mate’s infidelity or mate poachers that try to “steal” one’s mate for either a one night stand or for a long-term relationship. These threats have constituted problems for ancestral humans recurrently, which is why evolution in response has selected defenses that minimize these problems.

Jealousy is hypothesized to be an evolved adaptation that helps retain long-term mates by averting mate poachers (e.g. curtailing your partner’s contact with potential rivals and fending off rivals who show interest in your partner) and deterring mate’s infidelity (e.g. show vigilance to circumstances in which your partner might be unfaithful and furthermore increase own efforts to fulfill your partner’s desires so that he/she is less likely to cheat). Ancestral men and women that did care about or could detect threats to mate retention would have had a reproductive advantage over those who didn’t. Therefore their genes were passed down to future generations in a relatively greater frequency. Eventually, they passed down the genes associated with those traits along to modern humans. However, the specific situations that trigger jealousy are hypothesized to be different between genders.

Men and Women differ in the cues that trigger jealousy

Men and women that fail to retain their mates are faced with different problems when it comes to survival of their genes. Because of these differences, they tend to react differently towards situations that trigger jealousy. For men, there is always the risk of paternity uncertainty (not knowing whether the child is his or not). A woman, on the other hand, is 100% sure that the baby she is carrying is hers. This in turn brings up the possibility for cuckoldry –- that is, the risk of investing resources in another man’s child. Evolutionarily, cuckoldry would have posed a great cost to ancestral men, as they would have been giving up other mating opportunities in order to raise a child who wasn’t genetically related to him. Thus, men are predicted to be more sensitive to cues of sexual infidelity (when a partner pursues sexual interactions with another individual). By evolving mechanisms that are sensitive to sexual infidelity, he is protecting his ability to produce and invest resources in his own biological children.

Ancestral women, however, faced different consequences of infidelity. Because women must invest more biological resources in producing and raising children (e.g., carrying a baby to term, nursing, and so on) than men, our ancestral mothers selected male mates according to who was willing and able to invest in children in other ways.  If a woman lost her partner to infidelity, this meant that she also lost her partner’s time, attention, energy, and resources for both herself and their child(ren). The loss of his commitment would have had great implications for both her and her child(ren)’s survival. Thus, women are predicted to show a greater sensitivity to cues of emotional infidelity (when a partner forms a deep emotional connection with another individual), because this carried the risk of losing her mate’s resources to another woman.

These sex differences have been observed in a study conducted by, Buss and colleagues (1992). This study asked both men and women to choose between two very upsetting events: (a) their partner having sexual intercourse with someone else or (b) their partner falling in love with someone else. Now of course these situations are incredibly painful for both men and women, but in a “would-you-rather” situation there tends to be a common sex difference between men and women. It turned out that 60% of men found sexual infidelity more upsetting, while 83% of women found emotional infidelity more upsetting.

Not only is jealousy expressed as an emotional reaction, but it has also been shown to directly impact behavior. One study found that males responded with more anger, greater likelihood of relationship dissolution and less likelihood of forgiveness in response to sexual infidelity compared to emotional infidelity.

These sex differences are found consistently across different cultures. Buunk, Angleitner, Oubaid, and Buss (1996) found similar gender differences within the American, German, and Dutch cultures. Because values in the German and Dutch cultures de-emphasize sex differences and have more relaxed attitudes about sexuality compared to America, studies like this one provide particularly strong evidence for these sex differences being more than the result of learning, and thereby speaks strongly for the evolutionary psychological hypothesis. In short, because men and women have faced different adaptive problems caused by a mate’s infidelity (paternal uncertainty vs. diversion of resources), the sexes show differences in cues that trigger jealousy.

Jealousy: benefit or setback today?

In conclusion, jealousy is an evolved emotion that serves an important adaptive solution. Jealousy aids mate retention by causing behavioral tactics to fend off mate poachers, deter a partner’s sexual infidelity, and help retain long-term mating practices.

While too much jealousy can cause a relationship to end, or in extreme cases, even result in spousal abuse. However, jealousy is not all bad. Imagine being in a bar with your significant other. An attractive stranger approaches you, compliments your looks, and starts a conversation. There is no doubt that he/she is flirting with you. Your significant other is not bothered at all. He/she let’s you continue the conversation without interruption and might even take a seat to give you some privacy. How do you feel? Do you appreciate his/her open-mindedness or do you get upset by their lack of care? Most people feel hurt, and wish that the situation would provoke jealousy in their partner. In this case, jealousy can be very beneficial, because when shown in moderation it can be used to ensure greater commitment from a partner, increase psychological closeness and test the strength of the relationship.

Overall, jealousy is an influential emotion that can be either constructive or destructive in romantic relationships depending on how aggressively it is expressed. We should keep in mind that jealousy isn’t just a primitive feeling we’ve carried on through generations of humans; it serves to support mate retention tactics and behaviors that arise when situations such as mate poaching or a partner’s infidelity threaten to end a relationship.

Although men and women experience jealousy in different forms and for different reasons, they do share a similar goal. Ultimately, jealousy served the same purpose for our male and female ancestors alike: It helped them recognize and navigate problems in the wonderful world of mating.