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Is human evolution over?
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AtomicHorror wrote: »Yes you can. Your depth perception is a polygenetic trait, as are your capacities to judge motion, identify patterns (is that a bus?), weigh up risk and even feel fear. When you get hit by a bus, there's a good chance a whole bunch of genes or gene combinations are being selected against.
Not if you're looking the other way...
Seriously though, the suggestion that there is an inherent link between the human genotype and being hit by a bus seems an enormously contrived and speculative connection to me.Spina bifida does seem to have some genetic element, but I take your point. Assuming the reduced likelihood to reproduce or survive contains absolutely no inherited influencing factor then sure, it's not natural selection. But let's face it, there's bound to be some influence on the reproductive rate that comes from something inherited. What if the spina bifida were due to an inheritable aversion to folate intake expressed in the mother? Or what if spina bifida sufferer A has some unrelated genetic traits which make him marginally more likely to reproduce (assuming reproductive function has been preserved) than sufferer B?
What if this, what if that. Doesn't sound very scientific to me...Yes, it has increased the likelihood of reproduction for a great many genes. But it has absolutely not eliminated selection for and against them in various environments. CF sufferers still have an average life span that ranges from 20-40 years, which means that they're undergoing negative selection.
The average lifespan of a human for almost the entirety of the history of our species has been a lot less than 40 years. But anyway, my point wasn't that natural selection has been completely stopped, more that it has been significantly impaired in the current modern environment.If our evolution has resulted in us generating a society and environment in which more traits can be reproductively successful than by what criteria can we say that the effectiveness of selection has been reduced? Sure, we can speculate about catastrophic collapses of that society, as much as we could talk about major natural disasters, but those are unknowns. We could no more account for these when under mild selection than we could under strong selection. And indeed it seems intuitive to me that a pool of humans extant in great numbers and expressing a very wide range of genotypes is far better prepared for some hypothetical selective environment than a heavily-pruned population. There are plenty of "detrimental" traits in existence which could suddenly become very beneficial under all manner of circumstances.
Isn't that my point? That the current large population, coupled with diverse genotypes with a stable environment, medically advanced technology and knowledge, and non-evolution oriented social conventions have left us in a evolutionary equilibrium that awaits environmental disruption to initiate the next evolutionary step.Big digression there. Let's imagine we could homogenise the environment-influenced reproductive rates of all current genotypes. What happens then? For one thing we get genetic drift. The random rise and fall in frequencies of genes based on chance effects in reproduction and not influenced by environment. Genetic drift can result in the loss of genes from the gene pool by chance, which causes evolution.
Hmmm... might have to give you that one.
But I would suggest that the degree to which genetic drift (and the subsequent random, unselected for genetic changes) is a major contributory factor in Darwinian evolutionary theory is not obvious? (but I don't know enough about it to do more than pose the question...)Then there's sexual selection. That gene that doesn't kill you but causes those unsightly ear hairs of yours mean that the boys don't fancy you. Reproductive success is modulated, and we get evolution.
As per my original post, ugliness is not a very good argument for negative selection in such a large and geographically unimpeded species. There's someone for everyone... (thankfully!)And then there's mutagenesis. New mutations arise and become subject to natural selection, sexual selection and genetic drift whilst you try to figure out how to homogenise it relative to other genes.
They only become subject to natural selection if they are inheritable variations that improve the chances of survival and reproduction. My main point is that that is a tall order in current modern environment.Indeed, what of it? If the environment had not changed there'd have been no need for the selection in the first place. Also, evolution does not always act to change (that will even happen when there's no selection due to drift for example), sometimes it acts to conserve (countering drift).
"Indeed, what of it?" => "If the environment had not changed there'd have been no need for the selection in the first place."
Exactly.
I was just pointing out that instability of environment is an intrinsic and fundamental catalyst to evolution and that, by inference, stability of environment is an intrinsic inhibitor to evolution. I mean the lack of stable environments has played a major role in the evolution or our own species on numerous critical occasions. For ~150 million years over the Jurassic and cretaceous periods, the earth was a stable environment with dinosaurs being the most dominant and abundant land vertebrate. If the environment had remained stable, we wouldn't be here. It is only the instability in the environment caused by the K-T extinction event that allowed our small insectivore ancestors to increase rapidly in size and diversity. That is just one example, the oxygenation of the atmosphere around 2.5 billion years ago is another, probably the most important environmental disruption in the history of the evolution of most of the species of multi-cellular life on the planet.
Environmental stability as an inhibitor to evolution is probably most evident if you look at the work of genetic algorithms (it's much easier to see evolutionary change when you can speed up the process into a matter of minutes!). When a genetic algorithm is used to find a best fit to a particular problem (environment), there often comes a point at which no further genetic changes are made in subsequent generations as the "fitness" of the solution has reached a plateau and doesn't increase, i.e. the solution cannot adapt any further to its environment. Interestingly (and I use that term in its nerdiest sense!), this does not necessarily mean that the algorithm has found the best solution, just the best solution that arises from the evolutionary path taken. Other solutions may exist down different paths that may be better than this one, but the steps to that solution from the current one are not possible under the guidance of the selection parameters used, much in the same way that the tree hierarchy of natural life exhibits multiple different distinct evolutions for the same components (eyes, wings, etc). But the point is that stable equilibrium does occur.
A neat example of genetic algorithms at work on recognisable problems are the evolved creatures examples. One of the originals, but still one of the best presented:
Basically, I just don't see how you can suggest that stability of environment isn't an antagonist to the evolutionary process?0 -
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AtomicHorror wrote: »To skip to the punchline:
"Because evolution has no goal." For it to be antagonised it has to be going somewhere, but it isn't.
Ah, c'mon, the anthropomorphic goal was directly implied by the OPs question! In order to answer it all, one has to assume this implied goal (as we both have been up until now). The time for that point was your first post, it would have made for a short thread though!
Also, plenty of intrinsically goalless systems have individual goals for components of the system (e.g. a stock market has no goal in and of itself, but the stock brokers who make up the stock market certainly do have goals!)Selection is being antagonised by modern medicine to an extent and only with respect to certain traits, evolution can't be antagonised unless you're just not a replicator.
Well then, let's just leave it that we agree that natural selection is being curtailed by the modern environment (perhaps not completely on the degree). Personally, I think that means that evolution (as goal-oriented by the question asked) is definitionally curtailed too, but I'll shut up about it now!0 -
Ah, c'mon, the anthropomorphic goal was directly implied by the OPs question! In order to answer it all, one has to assume this implied goal (as we both have been up until now). The time for that point was your first post, it would have made for a short thread though!
If it was implied, I didn't pick up on it initially. My other points were valid anyway.Also, plenty of intrinsically goalless systems have individual goals for components of the system (e.g. a stock market has no goal in and of itself, but the stock brokers who make up the stock market certainly do have goals!)
What elements of evolution have a goal? The products of evolution have goals, but the process itself does not.Well then, let's just leave it that we agree that natural selection is being curtailed by the modern environment (perhaps not completely on the degree). Personally, I think that means that evolution (as goal-oriented by the question asked) is definitionally curtailed too, but I'll shut up about it now!
Perhaps this is more of a semantic thing. You seem to equate evolution with "change". Whereas I view evolution in broader terms with variation being one outcome of that process.0 -
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