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The naked love theory

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Matt Smith:

Human being share 98% of their genetic composition with chimpanzees. But there's quite a lot in that final 2% that sets us apart from our primate brethren. How we walk, how we look and how we think are distinctively and uniquely human. I'm Matt Smith and you're listening to a La Trobe University podcast.

Dr James Giles is a lecturer in the Philosophy Program at La Trobe University and has a theory relating to part of that 2% which he calls "The Naked Love Theory".

James Giles:

Well the Naked Love Theory is an attempt to explain a quintessentially human property among primates which is the property of hairlessness. We are the one primate who lacks a thick coat of bodily fur, a conundrum for evolutionary anthropologists and evolutionary biologists who have tried to figure out what the point of being hairless is. All other primates have hair; we don't. So it's very likely that we too at one time had bodily hair and lost it for some evolutionary reason.

Matt Smith:

Hair obviously performs a function to keep us warm. Why would we need to evolve without hair?

James Giles:

Well, that's one view of body hair, but since we lost our hair and it looks like we were hairless and without clothing for about a million years, it doesn't look like body hair served that function for us. Probably the original function of body for arboreal primates that lived in trees was to protect them from scratches and cuts and that sort of thing when you crawl through the branches. So that was probably the purpose that hair served for us in our arboreal state. Once we came out of the trees, there was no reason for the hair to be maintained but that wouldn't be a reason for it to disappear.

Matt Smith:

Why is the naked love theory more likely than the aquatic ape theory?

James Giles:

OK, well the aquatic ape theory is the view that we lost our hair due to an aquatic phase in our evolution. So people who believe this think that there was a time at which we became a more semi-aquatic animal than we are now. We lost our hair to help us get through the water, just like a dolphin and other mammals, whales, have lost their hair, in order them make them more streamlined. There are several things, I think, that make this theory unlikely. One is that we aren't really aquatically adapted. It's very difficult for us to swim and it doesn't seem that hair would make that much of a difference since we are so unaquatic. It makes a difference for a dolphin because it's a very streamlined animal.

Matt Smith:

Darwin theorised that hairlessness evolved through sexual selection. Was that closer to the mark?

James Giles:

I think that this quite obvious naked skin, especially female naked skin, has a great erotic significance and that shouldn't be overlooked. Darwin thought that there was no environmental reason to have become hairless and therefore it was probably something like sexual selection that encouraged that, and that he thought also that it started with females. As I mentioned female naked skin being very erotic, and his reason for thinking it started with females was that through all cultures across the world, women are more hairless than men. The problem with Darwin's theory is that he never gives an account of why that happened in the first place.

Matt Smith:

So this is where your theory comes in a bit. How do we start evolving as being hairless?

James Giles:

Well, most anthropologists agree that bipedalism was the prime mover of human evolution and I would ultimately tie hairless back to bipedalism also. This is really what distinguishes us from other primates and if you look at skeletons of the first bipeds, say Australopithecus, you will see that the upper part of the body is very apelike but from the pelvis down, it's very similar to human beings. So it looks like the first thing that evolved was the bipedalism, and the rest followed later. Once we became bipedal, then we had hands that were free. So the hands and the brain evolved together making tools, collecting food and so on, helped the evolution of the brain and the dexterity of the fingers.

One of the views is that there was a thinning out of the African rain forests about eleven million years ago and so various groups of primates were trapped in small groves of trees and the food sources were used up. They had to come down out of the trees, cross the savannah to find new food sources. Now if you look at other primates, you'll see that the infant itself holds on to the mother. The infant uses its toes and its fingers to hang on. When we became bipedal we lost our prehensile feet. Our feet could no longer hang on to things. People usually think that what an ape hangs on to with its feet are trees and vines and that's true, but there's something more basic that it needs to do in the beginning of its life, and that's hang on to the mother's fur. Once you become bipedal, you cannot hang on to your mother's fur any more. You just have your hands and that's not enough – you need hands and feet.

Now, if we were arboreal, we still lived in trees, that would have been devastating for us. The mother couldn't go through the trees looking for food, the infant would fall off, but because we became bipedal, the fact that the infant lost the prehensile feet wasn't such a big problem, because the mother now had free hands. She didn't need them to hold on to branches any more so she could compensate for the infant's lack of ability to hold on to her by her holding on to the infant. This was something that had to be selected for. So some mechanism was needed for the mother to want to hold on to the infant. This is where naked skin comes in to play. We know that infants feed a lot better when being breast fed if they have naked skin contact with the mother. There's less crying, less complaining, and they breast feed for longer. Mothers who also naked skin to skin contact with their infant while breast feeding report more affectionate love for the infant, and enjoy the breast feeding experience more. We also know that breast feeding can be erotic for mothers with over 40% reporting being sexually aroused during breast feeding. So it's quite clear that the skin to skin contact is very important in the mother-infant relationship. This would have been a mechanism that would have encouraged the mother to hold the infant and therefore have been selected for. What you would have would be a group of our ancestors, Australopithecus or before that, who had to carry their infants. Now some of those individuals just by genetic mutation and phenotypic variation would have less body fur than the other ones. And that would be passed on to their infants. The one with the less hair would just have a higher chance of probability of wanting to hold the infant. And that would be selected for, and that's what I call maternal selection.

Matt Smith:

Where does the theory go from here? Because this sort of maternal response would affect the development of a baby and development of the species as well as a result eventually wouldn't it?

James Giles:

Yes, what would affect the development of the species I think is infants don't stop developing once they grow out of their infancy. Adults carry with them memories from their infancy. Now, if you enjoyed skin to skin contact with your mother as an infant, it's very likely that in your sexual partner, you would also enjoy skin to skin contact with that person, and therefore be more predisposed to choose a sexual partner who is less hair covered than one who is more hair covered. And it's quite clear that somewhere in our evolution, people began to see more hairless individuals as being sexually attractive, and this is where sexual selection would be reinforcing the original maternal selection. A child's infancy becomes the blueprint for its later adult relationships. This is where we learn love and affection, in the maternal-child relation and we seek to repeat that in our adulthood. And we know through various studies too, that people who have positive relationships with their parents do select individuals as sexual partners who resemble them.

Matt Smith:

So this is really almost the evolutionary story of love as well.

James Giles:

Yes, this is the beginning of it, that's right. And it's interesting when you look at other primates, you see that human beings are unique among primates in that we live in a group and yet we form long-term attachments. Primates that have long-term attachments, like the gibbon, don't live in a group. They tend to live in a dyad of a male and a female, whereas chimpanzees, bonobos and gorillas who live in a group, they tend not to have long-term individual attachments. So that makes us quite unique in that way.

If you look further at sexual behaviour of the anthropoid apes who are our closest relatives, sexual intercourse tends to last only seven, eight seconds, whereas in human beings, that never happens. There have been various studies that have been done. There's a wide variation but it's probably true to say about ten minutes is the average of how long sexual intercourse lasts. That's eighty-five times as long as a chimpanzee's sexual intercourse. Why is that? Well, again, it's quite clear that human beings enjoy the erotic foreplay and skin to skin contact that's involved in that. If we were not hairless animals, we would have evolved in another way, sexually. And we may not have developed the erotic attachments that we have.

Matt Smith:

So why is that males have more body hair than females then?

James Giles:

Well, the naked love theory I think explains this very well. Because what is primarily selected for, according to this theory, is female and infant hairlessness, not adult male hairlessness, and this is exactly what you see. Women and infants are more hairless than adult males. And it's only when childhood finally comes to a close that you see male body hair appearing. Male hairlessness is important because the male also wants to have skin to skin contact with the female. If he's going to have a body of full fur, he's not going to be able to do that. But it would be secondary to the female and infant relationship which is the primary one. So probably females passed their hairlessness on to males, but only to a certain degree, after which it wasn't important that they were as hairless as the female.

Matt Smith:

That's all the time that we have for the La Trobe University podcast today. If you have any comments, questions or feedback about this podcast, or any other, you can send us an email at podcast@latrobe.edu.au. Doctor James Giles, thank you for your time today.

James Giles:

Thank you very much, Matt.