Since the optimal temperature for sperm production is a few degrees below body temperature, it is only logical that the testes be located somewhere outside the body where it is cooler, much to the chagrin of vulnerable males everywhere.Īs the testes moved outside the body, the vas deferens – the duct that carries sperm from the testes to the penis – should have headed south, too, but an unfortunate stroke of bad luck saw it getting hooked up and over the ureter. What possible benefit could have warranted such a migration? There are many theories, but the classic explanation involves temperature. Early in our history, the testes were located inside the body, but over the course of evolution, many mammalian testes moved down and out of the body. Similarly, the pathway of male reproductive organs in humans takes quite the detour. The path of the recurrent laryngeal nerve, as shown in the neck of a giraffe, takes an extensive and unnecessary detour. While in humans the detour is just a couple of inches, for a giraffe it’s as much as five metres. The human race should think itself lucky, however, as the ancestor that provided this nerve to humans is a common ancestor of all mammals. It now takes in the sights, detouring down the neck and looping under the aorta, before heading back up to the larynx. It would have made sense to start over, with the nerve running a direct route to the larynx, but the ‘no take-backs’ rule of evolution meant the nerve was instead forced to stretch. But as the necks of mammals lengthened, the nerve was forced to compensate, taking a much more meandering path through the body. In humans, this nerve supplies all the muscles to the larynx, opening and closing the vocal cords and allowing us to talk. In our fish ancestors, the nerve led directly from the brain to the gills. Today, what we call goose bumps are just a marker of our past, and serve very little purpose to our primarily hairless bodies.Īnother prime example of evolution doing its best with the materials provided is the detour of the recurrent laryngeal nerve. Our ancestors were once covered in fur, and they, too, may have puffed up their fur to look bigger or protect against the cold. Why? Think of a bird fluffing its feathers in a cool breeze, or a dog puffing up its fur when challenged. When we are cold or frightened, we get goose bumps. With that in mind, you can understand the evolutionary flotsam gathered around the human body. Now the human body is your plane, and natural selection is your engineer. After a few ‘generations,’ you’re going to end up with quite a few unnecessary parts, and quite a few recycled ones, too. You can’t remove a part or start over, but you can alter and repurpose pre-existing characteristics to make them more suitable for the environment in which they must operate. Each part that you add must improve the plane’s performance in some way. Richard Dawkins uses this analogy: Imagine you’re an engineer who has to build a plane from scratch… whilst in mid-air. The evolutionary changes that led to modern humans were not necessarily logical nor straightforward. Evolution has to work with what it's got, even when that has become impractical. The flipside of natural selection is that, while eliminating undesirable traits keeps evolution moving, it also means there are no take-backs and definitely no clean slates. An antelope that’s a fraction faster than its fellows is more likely to survive and carry its genes into the next generation. Traits that give an animal any advantage over its rivals are fiercely supported. To develop a superior trait within a species, all inferior models must be destroyed, erasing undesirable characteristics from the gene pool. Traits that may once have given a distant ancestor the edge it needed to survive have now become impractical and, at times, detrimental. We are, after all, one long string of compromises. The human body is riddled with imperfections and vestigial traits. The traffic is crawling, and there are only two options: keep on trucking, or get off the road. Here, the road is one-way and there are no U-turns, hook turns or roundabouts. We’re just drivers on this evolution highway, and our vehicle is natural selection. Unfortunately, evolution sometimes takes an unexpected turn, and the evidence for this is written all over us, too. Every trait that has, or once had, a purpose provides a rich map of the history of our evolution. Every characteristic of our bodies is the result of millions of years of evolution. That’s what Richard Dawkins said in his book The Greatest Show on Earth.
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