Columns

It’s time for a column about evolution. Don’t worry, I’m not going to preach about the problem with creationism – that debate has been going on for years, and by this point most people know evolution is real, and a few will never be convinced otherwise. Aside from the occasional “Challenge to Evolutionists” or a new fossil that could “Finally Prove Evolution”, for the most part we’ve seen all the evolution we’re going to in the content of that debate.

I’m sure you sensible people know that evolution is real, but if you haven’t studied evolutionary biology, you mightn’t know too much about the details. I’ll elaborate.

Natural selection is so elegant! It’s simple and intuitive once explained, but the first time it occurred to Darwin (and Wallace) it must have been mind-blowing. Basically, if organisms in a population have variation in their physical appearance and behaviour, if that variation is inherited by babies from their parents, and if not all organisms survive (because nature is cruel, like when the lion eats the antelope and David Attenborough’s soothing voice makes you want to cry), then babies with “good” variations will survive better, and they’ll have their own babies with good traits too. Ta-da! A population with traits suited to the environment – natural selection!

This explanation often leads people to assume that selection results in “perfect” organisms. Because selection can only “choose” from existing traits, lots of strange structures occur when a nearby structure changes thanks to selection.

The giraffe’s vagus nerve is an example. All mammals have this nerve – it starts at the brain, travels down around the arteries of the heart, and loops up to the voicebox. During embryological development, the nerve takes this path as it grows through the body. In mammals with short necks, this makes sense, but giraffes have a two-metre long neck, so their vagus nerve travels all the way down and then all the way back up their neck! Because this pattern of growth evolved before the long neck of the giraffe, the nerve will never be able to grow directly to the voicebox.

A sexier example occurs in humans – the vas deferens is the tube through which sperm travels from the testes to the penis. Like the giraffe nerve, it takes a crazy route. The vas deferens loops all the way up over the bladder, then back down to the penis. This is because human testes descend during development, looping the vas deferens over the bladder as they go, whereas in other mammals the testes don’t descend. This leaves the poor sperm with a fair distance to swim to reach their goal – although perhaps that makes the fun part last longer? For that, you can thank the science, bitches.