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In a new study, evolutionary biologist Sergey Gavrilets makes a fascinating claim for how monogamy took root several million years ago

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According to one evolutionary biologist, the modern family might look very different had some scrawny male hominids not found a clever workaround to having to physically compete against strong alpha males for mates. (© 20th Century Fox Film Corp. All rights reserved. Courtesy: Everett Collection)

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According to evolutionary biologist Sergey Gavrilets, the modern family might look very different had some scrawny male hominids not found a clever workaround to having to physically compete against strong alpha males for mates. In his latest study published in the Proceedings of the National Academy of Sciences, Gavrilets suggests that weaker males, in lieu of being promiscuous, fawned over a single female. By providing her food, a male would earn that female’s trust and sexual fidelity. In this scenario, the pair’s offspring naturally benefited, as they were more likely to survive under the watchful gaze of two parents.

So, let’s start by going back in time. Before monogamy and the nuclear family, how did hominids live?

Judging from the fact that our closest relatives are chimpanzees, I think we can expect that our social life was pretty similar to what they have now, which is basically small groups. As far as mating relationships are concerned, there is a very strong dominance hierarchy in chimpanzees, where alpha males completely dominate the group and get the majority of mating. It is a very despotic society, and I think that is what our ancestors had as well.

When do you start to see a transition from promiscuity to pair bonding?

We know that humans separated from chimps somewhere around 6 or 7 million years ago. In hunter-gatherer societies, typically, each man has a single wife. So it happened somewhere during this interval that is several million years long.

There was a series of papers in the journal Science three years ago that described a fossil, known as Ardipithecus ramidis, for the first time in detail. This fossil is 4.4 million years old, so about one million years older than [the famous hominid specimen named] Lucy. People claim that this new species already shows signs of significantly reduced competition between males. Both the sexual size dimorphism [or difference in size between males and females] and the size of the canine teeth are dramatically decreased. They are much smaller than you would typically see in species with very strong between-male competition. The claim that researchers made is that this pair bonding in our lineage is something that is more than 4 million years old.

As you say, it was a “social dilemma” for males to shift their focus from competing for mates to caring and providing for one mate and their collective offspring.

From an evolutionary point of view, everybody is interested in creating a number of surviving offspring. How can males do it? Well, one strategy for males is to mate with as many females as possible. We can have a lot of offspring, but we are going to completely neglect them.

On the other hand, there is an alternative strategy. Instead of maximizing the number of matings, you can maximize the investment in the offspring. This way, even if you have a small number of offspring, most of them survive, and you can be better off. That is basically the situation that I model in my paper.

One is beneficial for the male—to increase the number of matings. But, in this case, a lot of energy and effort is wasted on the competition. Then, there is this other strategy—investment in the offspring or in the females. This strategy will definitely be beneficial for the group as a whole, but because of this existing logic of competition in the group, males are forced to invest in a low fitness solution. They are forced to compete rather than to invest.

How did the transition happen?

We have this group, and there is a strong dominance hierarchy in it. There is that alpha male who can beat up everybody and chase away all males. He is not going to give up his power. Males on the bottom of the hierarchy cannot do much alone against this alpha guy, but they might be willing to try a different strategy.


According to evolutionary biologist Sergey Gavrilets, the modern family might look very different had some scrawny male hominids not found a clever workaround to having to physically compete against strong alpha males for mates. In his latest study published in the Proceedings of the National Academy of Sciences, Gavrilets suggests that weaker males, in lieu of being promiscuous, fawned over a single female. By providing her food, a male would earn that female’s trust and sexual fidelity. In this scenario, the pair’s offspring naturally benefited, as they were more likely to survive under the watchful gaze of two parents.

So, let’s start by going back in time. Before monogamy and the nuclear family, how did hominids live?

Judging from the fact that our closest relatives are chimpanzees, I think we can expect that our social life was pretty similar to what they have now, which is basically small groups. As far as mating relationships are concerned, there is a very strong dominance hierarchy in chimpanzees, where alpha males completely dominate the group and get the majority of mating. It is a very despotic society, and I think that is what our ancestors had as well.

When do you start to see a transition from promiscuity to pair bonding?

We know that humans separated from chimps somewhere around 6 or 7 million years ago. In hunter-gatherer societies, typically, each man has a single wife. So it happened somewhere during this interval that is several million years long.

There was a series of papers in the journal Science three years ago that described a fossil, known as Ardipithecus ramidis, for the first time in detail. This fossil is 4.4 million years old, so about one million years older than [the famous hominid specimen named] Lucy. People claim that this new species already shows signs of significantly reduced competition between males. Both the sexual size dimorphism [or difference in size between males and females] and the size of the canine teeth are dramatically decreased. They are much smaller than you would typically see in species with very strong between-male competition. The claim that researchers made is that this pair bonding in our lineage is something that is more than 4 million years old.

As you say, it was a “social dilemma” for males to shift their focus from competing for mates to caring and providing for one mate and their collective offspring.

From an evolutionary point of view, everybody is interested in creating a number of surviving offspring. How can males do it? Well, one strategy for males is to mate with as many females as possible. We can have a lot of offspring, but we are going to completely neglect them.

On the other hand, there is an alternative strategy. Instead of maximizing the number of matings, you can maximize the investment in the offspring. This way, even if you have a small number of offspring, most of them survive, and you can be better off. That is basically the situation that I model in my paper.

One is beneficial for the male—to increase the number of matings. But, in this case, a lot of energy and effort is wasted on the competition. Then, there is this other strategy—investment in the offspring or in the females. This strategy will definitely be beneficial for the group as a whole, but because of this existing logic of competition in the group, males are forced to invest in a low fitness solution. They are forced to compete rather than to invest.

How did the transition happen?

We have this group, and there is a strong dominance hierarchy in it. There is that alpha male who can beat up everybody and chase away all males. He is not going to give up his power. Males on the bottom of the hierarchy cannot do much alone against this alpha guy, but they might be willing to try a different strategy.

It is well known that what occasionally happens with chimpanzees is provisioning females and exchanging food for a mating opportunity. The males start doing that, but it is not enough, because females can just take food and still mate with the alpha male. So we need something else. That something else that I included in the model was the idea of mutual choice.

In a sense, the whole species gets “self-domesticated” by the following process. Males are selecting females who are more and more faithful to them. And, simultaneously, females are selecting males who are better providers. We have this process known in biology as co-evolution, when changes are happening in two different groups.

You call this “the most important sexual revolution for our species.” Why?

For humans, the development of human offspring is very long. Chimpanzees, I think, become independent and able to live on their own by the age of three or four. In humans, it takes three or maybe four times longer. So, help is necessary. Males are the obvious source of this help.

Cooperation at all levels has been extremely important in human society. The easiest way to establish genes for cooperation and altruism is if these traits are directed toward your relatives. To do that, you need to know who they are. So, by establishing this pair bonding, it is not just that males help, but also the knowledge of the kinship networks allows for cooperative behavior.

What is your next big question?

I am always interested in what I view as the ultimate speciation event, the origin of our own species. There were a lot of social and behavioral changes, and not just genetic, physiological or developmental changes.

I have one very exciting project that I am trying to publish now that could explain the origin of our moral values and then also the origin of social complexity and the origins of chiefdoms, states and empires. Basically, I am looking at different things happening just before and soon after that transition from apes to humans.

This interview series focuses on big thinkers. Without knowing whom I will interview next, only that he or she will be a big thinker in their field, what question do you have for my next interview subject?

I would ask something personal. Ask something not related to the work. What would they like to have more opportunity to do or more time to do if they had the chance?


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Comments (1)

that puts much of the bible....old testament texts...into context of social evolution. Same for other religions, but none as well formulated as the bible. Also see Proverbs 8....fascinating take on evolution. You could then argue that the new testament is again a quantum leap

Posted by Klaus Mager on July 22,2012 | 11:24 AM



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