Saturday 20 November 2004

Pic of the day: What's this? It is one of the greatest inventions of all time. (And think twice about trying this at home, kids.) Screenshot from the anime Final Approach.

650 million years of rears

It started with the invention of the worm, that's how I see it. As humble as they come, the worm is still the blueprint of higher life. It sports a dashing new feature, the anus, at roughly the opposite end from the mouth. Unlike jellyfish, sea urchins and an unbelievable number of extinct species, the worm expels the end products of its digestion at a safe distance from the food intake, setting a new standard in hygiene. It is also wisely oriented so that the mouth is in the direction it moves, and the anus where it is moving away from.

When the first multicellular animals emerged that were large enough to leave fossils, the world had recently emerged from a disaster beyond imagination, commonly called "Snowball Earth", where life had been very nearly reset. But what emerged was a remarkably wide range of body plans, each of them as alien to one another as the octopus is to us, if not more. It looks like the result of a divine brainstorming, though less pious scientists are known to mouth the word "acid". So alien are these animals that in one case respectable scientists have long debated which side was up. Yet, with the next reboot (now called the Cambrian Explosion) the sons of the worm emerged victorious.

Most important for us, the chordata had arrived. This refers to animals with a spine. The elongated form that made possible "assembly line" digestion was now reinforced with a high-speed data line for the nervous system, a backbone so to speak. Although the actual bone seems to have been added after the neurons that are now safely hidden inside it. The new feature made it possible to increase the size of the animal further. Another necessity for large size is a way to rapidly distribute oxygen and nourishment to the cell, namely blood. Blood again needs to be purified from various by-products of the metabolism (most notably nitrous compounds from breaking down protein). Enter the kidneys. And exit the urine, wisely directed to the existing exit. After all, what kind of retarded creature would pee in front of itself? Wait, don't answer that.

***

There is one other small detail in life, beyond eating and excreting. For less spiritual beings such as fish, the true meaning of life is to reproduce. And a good thing too, or we would likely not have been here. So yet another organ there is that empties itself through the common exit. First the female fish expels her eggs, then the male (another truly ancient invention) covers them with sperm.

This method was so successful, it was continued by the amphibians when they conquered the dry land. Or at least the wet land. Although most of them croaked a very long time ago, their reign was long and largely uncontested until they were ousted by their own children, the reptiles.

The reptiles had plenty of new features to make them less dependent on staying near water. One of the most notable was eggs with shell. But this meant the male could no longer tactfully wait until the eggs were laid before he applied sperm. He had to deposit his seed inside the female's cloaca while there was still no sign of egg. I bet it must have felt strange the first time. But from that day on, the female's backside became the center of the male's life.

Largely it is so even today, for the many species of reptiles and birds have retained the simplicity of design, especially on the female side. Even one branch of mammals, the monotremes, have a combined opening. But as most of us have found out by now, this is not the case for placental mammals.

Of course, by then the males had already for millions of years proudly waved their penises, an invention that made it easier to deposit sperm where it belonged. (Until then, the male and the female would just join their rear ends and hope to exchange the right ingredients. This must have been very awkward and went out of fashion for most species long ago.) For reasons probably only known to the Intelligent Designer, the penis also became an external urinating appendage, unlike in our friends the insects where it only has one use. Yes, they also got one, and even some cephalopods have separate "arms" for this purpose. None of them would even consider trying to pee with those, though. You'd think that it would make more sense to let the liquid wastes go with the solids to that other exit. Well, that didn't happen. Another thing to ask when we meet our Maker, I suppose. (May that day still be a long time in the coming.)

At least some sexual equality was restored when most of the mammals got two separate exits for females as well. I don't know whether this was a driving force in the overall higher intelligence of mammals compared to reptiles, but for the longest time the two openings stayed close together, still on the backside, and it was kinda crucial to find the right one. The monkeys and apes should supposedly be even a bit smarter, but perhaps they were easily distracted. Anyway, it was decided that the poor males needed help to find out where to stick it, and so in many species the females developed visual cues such as colorful swellings and stuff.

And then came Homo Sapiens, the smartest of the smart. Due to its overwhelming brainpower, the human male could not be trusted to tell the vagina apart from the rectum even with flashing signs pointing to the right one (and probably most females pointing to it as well). So, in a further design improvement, the reproductive apparatus was moved further away from its original co-location with the anus, and placed much further down and easily accessible from front. It is still accessible from the rear, just in case. Idiot proof, for the first time in evolution, because for the first time in evolution it was necessary to deal with idiots who trust their own intelligence higher than their instincts.

We've come a long, long way since the worms. The rear is no longer the only road to bliss and the continuation of the species. Indeed, it has been dethroned to the point where it can be seen on Japanese TV, unlike actual genitals (and nipples, for some reason). It still remains somewhat decorative though, don't you think? Especially when not in use for its original purpose. And whenever you see one, think of the worm. Oh yeah, we've come a long way, baby!