Since I mentioned retrotransposons and accumulated retroviral genomic litter in yesterday’s post, I’ll get a bit philosophical about that today. I’ve had a couple of interactions with people who read about all this and didn’t realize what state our genomes are in, and they were struck by all this. As they should be! It really is weird that we are all carrying around eroded bits of DNA sequences that got inserted into our genome from back before we were even human beings. And it’s similarly weird to realize that in many cases we’ve adapted to those sequences and found a use for them as spacers and scaffolding.
But that’s what goes on down there. Accidents happen constantly. Most of them are silent, and most of the rest are harmful to a slight or serious degree, but the ones that actually turn out to be useful get their chance. Did you up and duplicate a whole gene, so that now you have two copies of it? Well, OK, run with it. Maybe having double the expression is a good thing, or maybe it’s good to have backup expression if something goes wonky with one copy. Over time, both copies will pick up mutations of their own, though. Most things do. But maybe one of those will turn out to be useful in a different way. Congratulations! You now have a new receptor subtype or protein isoform, off doing its own thing. As I’ve said here before, evolution’s motto is “Hey man, whatever works”.
And the definition of “works” in this context is easy to state: did you live long enough to pass on your genes to the next generation? Did something make you a tiny bit more likely to be able to do that? That’s all you need. Those questions are tied in with the environment around you, of course. If something has changed – a food source has vacated the area, or the climate is shifting (heat, cold, rain, drought), or a new parasite or predator has moved in – then previously underappreciated mutations might come in handy. At the same time, some of your hard-won gains in another direction might suddenly be a burden. The deck gets shuffled all the time, lightly or thoroughly (perhaps there’s been an asteroid strike?)
What needs to be emphasized is that outside of living creatures, we have no good analogies to this. The closest thing might be the actions of geologic time and processes on the landscape, producing weird and various rock formations and terrains. Who could have ever predicted a limestone cave and its formations from first principles, or the striations and colors of the American Southwest or Australia’s? Outside of geology, if someone told you about planets and atmospheres and water vapor, could you have predicted the varieties of clouds, from billowing cumulus through thunderheads to cirrus horsetails, and the constant interplay of light and color among them? Could you have built up the idea, the picture of a blazing end-of-the-world sunset from just thinking it through? But even those don’t have the reproductive fitness aspect; they don’t have that thumb on the scale. We’re more startling than sunsets and crazier than caves. Living systems build complexity in a way that nothing else does, and they do it in a way that utterly foreign to our rational tool-building minds.
So we take them for granted. Maybe it’s because there are no examples of this at all until we look at living things, and then we see so many examples that we don’t know what we’re looking at any more. Zero evolutionary weirdness, or nothing but – it’s no wonder our perceptions are off. We’re surrounded by moving, energy-shifting self-directed hunks of insanely complex nanotechnology, performing functions we don’t completely understand in ways we don’t completely understand. I’m talking about your cat, or your houseplant in the window. We ourselves are more of the same: a pile of ridiculously complicated interlocking systems that we absolutely don’t really understand, and the only reason that we can use the word “understand” (or any words at all) is because of even more insane emergent phenomena called “consciousness”, “intelligence”, and “language”. We wouldn’t believe that such creatures, such constructs, such staggering lurching heaps of molecular machinery were even possible if we weren’t ones ourselves. But since we are, we just don’t think about it much.