The Evolution of How and Why Monogamous Species Came To Be 

The article above by reporter Carl Zimmer is titled “Monogamy and Human Evolution,” and it centers on the reasons and effects that primates such as humans began forming monogamous relationships after the split with our chimpanzee and baboon ancestors. Zimmer moves quickly from Dr. Dieter Lukas’s (University of Cambridge) research that animals would benefit from being less monogamous to Dr. Kit Opie’s (University Cambridge London) theory that humans evolved larger brains thanks to the addition of monogamous relationships. These may seem counter argumentative, but Zimmer continues, saying: “Each species faces its own special challenges — the climate where it lives, or the food it depends on, or the predators that stalk it — certain conditions may favor monogamy despite its drawbacks.”

After reading the first paragraph, I was slightly confused by the article’s neglecting to address how overpopulation is currently a huge issue with humans and certain animals. I understand that maximum reproduction is often a sign of being the fittest, and thus those who produce more offspring are less likely to become extinct. At the same time, it’s been proven time and time again that one of the largest factors in extinction comes from overusing resources. My initial concern was then gratified by Zimmer’s description of different theories that scientists have gathered on why animals evolve into forming monogamous relationships (i.e. females being more widespread vs. the threat of infanticide). Dr. Opie’s explanation that many animals may face infanticide directly relates to my qualm: since fathers began sticking around to provide food and protection for their offspring, it means they were concerned about his offspring’s livelihood in respects to other predators. If fathers leave after every mate, than the likelihood of their offspring surviving decreases. That in it of itself decreases that specie’s ability to be the fittest.

Along these same lines, Zimmer then explains the aftermath of primate fathers first beginning to care for their children: “The extra supply of protein and calories that human children started to receive is widely considered a watershed moment in our evolution. It could explain why we have brains far bigger than other mammals.” Is it also possible that if more species start forming monogamous relationships, that natural selection will allow other species to evolve into more human-like animals? Or would this contradict Dr. Lukas’s idea that monogamy, even in the 9% of mammals that adhere to it, prevents male mammals from having more offspring, “mating with lots of females,” and thus being the fittest?

At first read Zimmer’s rhetoric is slightly confusing because of his contradicting reports that monogamy is less beneficial and yet also caused the development of current day humans. Though after reading it again, I realized that the stark change from one piece of evidence to the next completely coincides with how theories of evolutionary effects develop and adapt to newer evidence. Much like the theory of evolution itself, our understanding of how and why evolution takes place is continually changing and growing. The idea that monogamy can be beneficial to one species and harmful to another is certainly not new, and is even reinforced by University of Montreal’s Bernard Chapais’s statement that, “The human mating system is extremely flexible.” Even within species, mating systems and monogamy isn’t always consistent. This fact too proves the idea that evolution is constantly, and will always, force animals and humans alike to adapt to their current needs and surroundings. 

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9 Responses to The Evolution of How and Why Monogamous Species Came To Be

  1. freddie1994 says:

    I, personally, would agree with the idea that monogamy leads to both parents protecting, feeding and raising their offspring, which would certainly lead to a higher chance of survival for that offspring, but I wouldn’t have thought this would lead to an increase in brain size. Surely a bigger brain size would lead to an animal understanding the choice to either stay and ensure the survival of less offspring, or leave and try and have many offspring with a lower chance of survival. That being said I’m not a scientist so I obviously can’t say with any credibility whether bigger brain size led to monogamy, or monogamy led to brain size. As the original post mentions 9% of mammals are monogamous, and the article mentioned that 25% of primates are monogamous, but do we know if their brain sizes have increased, and if they have, was it before or after that species became monogamous? Crocodiles (yes I know they are reptiles) have changed very little since the time of the dinosaurs, and to the best of my knowledge (happy to be corrected if I am wrong) crocodile offspring are on their own at around three months old – meaning zero parents raise them, let alone one or two – yet crocodiles haven’t evolved, devolved, or become extinct in hundreds of millions of years. There are plenty of successful polygamous and monogamous species, so in my opinion this seems to be a minor factor in terms of causing evolution.

  2. running95 says:

    This article is extremely intriguing and it is very believable that the act of monogamy has produced a more nutritiously stable species as a whole. However, where I would beg to differ is on the point that monogamy directly led to an increase in brain size and complexity within humans. Looking at this idea from a purely genetic standpoint it seems more than highly unlikely (if not absolutely absurd); if a parent modifies some part of his or her body after embryonic development, that modification will not pass to the next generation. Therefore, even if a parent takes in more nutrients even as a young child, those nutrients will have little to no effect on the brain sizes and capabilities of the next generation, and despite possibly improving brain development I would need more evidence to believe that an increase in parental nutrition could lead to a genetic modification in offspring. Overall, however, I did appreciate this article and I did find it very interesting and compelling, but I only wish it offered a bit more genetic research to buttress the brain enlargement argument.

  3. After reading this article I was interested how the theory of evolution was applied to societal behaviors and not just anatomy and design. I agree with the evidence about how monogamy is better suited for some species and polygamy suited for others. I also agree on the fact that infanticide is a logical reason for species to favor monogamy. However, to play devil’s advocate, polygamy is also a valid adaptation to the threat of infanticide. More offspring would increase chances of at least one offspring to survive and pass on genes to the next generation. Many mammals give birth to litters of offspring to increase the chances that offspring will grow to maturation. In this case, monogamy is less beneficial because it results in less offspring, especially in animals that only give birth to one offspring at a time. This behavior is not economical with time or resources. Humans usually only give birth to one offspring at a time. It is not likely for women to give birth to more than one, and even less likely to give birth to over two babies at a time. From a biological and anthropological standpoint, polygamy would be a better idea for humans with social and political ideas aside.

  4. roberly2 says:

    I found the article hard to read, personally, for much the same reason the author of the response found it to be confusing; if monogamy is a product of biological evolution, then why are we plagued as we are with the marital discords that we are in this day and age? Biologically, we as a species are meant to devote significant time and energy to our young to ensure the maximum survival of our species, the males are meant to provide food and shelter, protection for their young as well, and yet here we are in the midst of a constant struggle to protect children from abusive homes, extreme poverty, and parental neglect. I believe the article is fundamentally flawed in not addressing the pervasive social issues and how they, not biology, are the primary indicator of the survivor-ship of our species. We may be biologically evolved to pursue monogamy and to provide constant care for our young, but we are socially inept in many ways and it is this intense disconnect between our minds and our biologies that causes us to have so many social issues. Yes, the article presents several interesting ideas about evolution and social interaction, but it is ultimately neglectful in its presentation of the realities that exist for the human race.

  5. sm1414 says:

    I found the article to be interesting and confusing. I also think that the article ignores an important cause of human evolution: an increase in global temperatures. One of the first exhibits at the National Museum of Natural History is about how a warmer climate allowed for the increase in brain size that is associated with our species. Like an earlier commenter, I agree that the nutritional argument about how humans gained a larger brain is incomplete. It is not possible for parents to pass on habituated traits (traits that are gained during a life time that are not genetic), but it is possible that the environment in which the species lived had a greater amount of food. This would have been a direct result of a warmer climate since vegetation that results in food tends to grow better in warmer weather. In this sense, the environment would have had more food and thus led to a larger brain size in both parent and offspring. I would also agree with an earlier post that monogamy is actually bad for the human race because it prevents the spread and intermixing of better genes. Not only does it decrease the fitness of both parents, but it also prevents new combinations of genes which may produce better offspring from being created.

  6. nicolina1215 says:

    In response to dantesnuggles, I agree that polygamy is a practical way of life for animals that are more worried about breeding multiple offspring. Though when it comes to humans, I believe that there are more benefits in developing countries than there would be for members of developed countries. In an article by Psychology Today, Ph.D. Nigel Barber explains three common reasons why humans would choose to live in polygamous relationships: “So humans turn to multiple marriage for the same three basic reasons that birds do (scarcity of males, selection for disease resistant genes, and defense of breeding territory and its economic equivalents.)” On the other hand, there are many psychological damages to human offspring that are raised in polygamous households, though I know you said social and political ideas aside. That being said, I was more so aiming at the idea that monogamy and having one consistent father and one consistent mother present throughout childhood, versus having only one mother to fend for the family, posed extremely positive results when humans were less evolved. To your point, more offspring is more sensible to increase chances of one surviving if the parents don’t plan on providing for those offspring. As humans are seeing today, having more children can often be a drawback because of the coinciding fees that go along with the upkeep of a satisfied family.

  7. shoutoutjfk says:

    I would like to address something you (nicolina1215) discuss in the second paragraph of your entry. You said that you were confused with the idea of maximizing reproduction due to the necessary allocation of resources for each new individual. From an ecological perspective, overpopulation is a definite issue, though it’s not one evolution addresses directly. Every population’s initial goal has always been to increase in size to allow occupation of some niche. Without a species’ will to procreate as much as possible, it would have been very difficult to accumulate enough individuals to not become extinct before existing long enough to even be considered a population. Your point regarding resource allocation is valid, but would not have been viable from a natural selection standpoint. You may ask: so if a population were to thrive and grow large enough to use up all of its available resources, what would happen? This happens in nature quite often and the result is merely a stoppage in the exponential increase of the population. Instead, the population reaches a point of stability and zero growth known as the carrying capacity (represented by the symbol “k”). To tie back to the original focus of the article, this phenomenon of carrying capacity is actually tied to monogamy. In humans living in relatively wealthy nations for example, the trend of population growth is to remain at zero. From a pragmatic approach, this is because although people still have a desire to have children, the children are no longer required to perform laborious duties. Thus, humans in these nations are likely to engage in monogamous relationships with about two children. Monogamy therefore can be viewed as a sign of basically mastering survival.

  8. foldervral says:

    Monogamy and polygamy are both useful in their own ways as evolution progresses. Toward the beginning of evolution I believe species that support polygamy had a better chance of surviving due to the the mass production of a diverse offspring. The pairing of different mates will result in more recessive traits occurring giving these traits a chance to help the species evolve in principle of survival of the fittest. At the same time this is only really useful for the prey portion of the foodchain because an overpopulation of predators would cause a massive drain on resources. The use of monogamy in evolution may slow down the actual evolutionary process it does account for a higher survive-ability rate in young. In current society humans mostly use monogamy due to a lack of a survival of the fittest environment. The contradiction that both can be considered good methods is supported in the article. What the article fails to mention is any psychological conditioning that may impact a species decision to monogamous or to support polygamy. This raises the simple question of nature vs. nurture which can be viewed while looking at the diverse cultural views of monogamy and polygamy over the past millennium.

  9. djrosato says:

    I tend to disagree with nicolina1215, I don’t find Zimmer’s rhetoric disjointed or contradicting at all. Zimmer points out the clear benefits of monogamy for human evolution and uses examples referencing the lengths chimpanzees and our other evolutionary relatives must go to to make sure they reproduce, such as the chimpanzee’s increased sperm count and their tendency to fight over prospective mates. Monogamy helps us bypass that. With regards to the constant mention of our increased brain size, I don’t believe that that was one of the points Zimmer was trying to relay. While the rest of his article was rife with examples and even the occasional link to an outside source, his statement about the evolution of our brain took up only two and a half short paragraphs and using the word “could.” To me, this seems like a more offhand comment as opposed to it being central to the topic. After all, this article is about the evolutionary puzzle that is monogamy and how it came to be. Increased brain mass may have been a benefit of eating meat, which monogamy made possible, but it wasn’t one of the reasons that we were biologically pushed to this lifestyle.

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