Unique part of the human body that evolution cannot explain

human body There is a machine whose many parts – from the microscopic details of our cells to our organs, eyes, liver and brain – have been fitted together over the four billion years of our history.

But scientists are still confused about why we evolved into this particular form. For example, why do humans typically have a chin? And why, relative to body weight, is the size of a human testicle three times the size of a gorilla’s but one-fifth that of a chimpanzee? As I show in my new book, The Tree of Life, we are still searching for answers to many of these “why” questions. But we’re starting to find answers to some of them.

story of Development Tells us how, starting from simple beginnings, each species was created, when each component that makes up a living being was added to its blueprint. If we climb the evolutionary tree of life, we can follow a winding path that visits increasingly specific branches that relate to a species. For example, we humans were animals before we became vertebrates; Mammals before evolving into primates and so on.

Each branch of the group of species we share traces the order in which our body parts emerged.

A body and an intestine (invention of the animal branch) must have come before the backbone and limbs (vertebrate branch); Milk and hair (mammals) came before nails (primates).

There is a way we can study separately the problem of why we evolved all these body parts, but it only works if the trait in question evolved more than once on different branches of the tree of life. it was repeated Development is called convergence. This can be a source of frustration for biologists because it confuses us about how species are related. For example, swallows and swifts were once classified as sister species. We now know from both DNA and comparisons of their skeletons that swallows are actually closer relatives to owls than to swifts.

Size matters when it comes to evolution

But convergent evolution becomes useful when we consider it as a kind of natural experiment. The size of the primate testicles provides us with an excellent example. Abyssinian black and white colobus monkeys and bonnet macaque adult males are approximately the same size. But, like chimpanzees, humans, and gorillas, the testicles of these similar monkeys vary greatly. Colobus testicle weighs only 3 grams. In contrast, the testicles of macaques weigh 48 grams.

You can come up with several plausible explanations for their different testicle sizes. Large testicles may be the equivalent of peacock tails, which are not useful in themselves but are attractive to women. But perhaps the most plausible explanation concerns the way they mate. A male colobus monkey competes fiercely for access to a harem of females who will mate exclusively with him. Macaques, on the other hand, live in peaceful mixed troops of about 30 monkeys and have a different approach to love where everyone mates with everyone else: males with multiple females (polyandry) and females with multiple males (polyandry).

Colobus can survive by producing minimal sperm with its harem – if one drop is enough to produce a child, why produce more sperm? For the male macaque, reproductive competition occurs in a battle between his sperm and the sperm of other male macaques that mate first or later. A male macaque with larger testicles should make more sperm, giving him a greater chance of passing on his genes. It’s a sensible explanation for their different testicle sizes, but is it true? This is where convergent evolution helps.

If we look at the entire mammalian branch of the tree of life, we find that there are several groups of mammals that have all evolved testicles of different sizes. In almost all these different cases, larger testicles are consistently found in polygynous species and smaller ones in monogamous species.

With small testicles, silverback male gorillas have sole access to the harem. Chimpanzees and bonobos with large testicles are actually highly sexual. Meanwhile, dolphins’ testicles may be the largest of all mammals, making up 4 percent of their body weight (equivalent to human testicles weighing about 3 kg). Although it is naturally difficult to study the sex lives of wild dolphins, spinner dolphins at least live up to our expectations, engaging in mass mating events called woozles.

It was thanks to the many observations provided by convergent evolution that we were able to discover this consistent correlation between testicular size and sexual life in mammals. And as for humans, our testicles are somewhere in between in size, you can make it whatever you want!

But what about the human chin?

The human chin has been fertile ground for debate among scientists over its purpose. Like the testicle, there are a half-dozen plausible ideas to explain the evolution of the human chin. This may have evolved to strengthen a struggling caveman’s jaw. The chin may have evolved to accentuate the splendor of a man’s beard. It may also be a by-product of the invention of cooking and the bland food it produces – a functionless facial bulge left behind due to the receding tide of a weak jaw.

However, interestingly, a chin cannot be found in any other mammal, not even our closest cousins. NeanderthalThanks for the specification a wise man Chin, while we have a rich set of possible explanations for its evolutionary purpose, in the absence of convergent evolution, we have no sensible way to test them.

Some parts of human nature may be destined to remain a mystery.