Genetic variation from one generation to the next is incremental - not a matter of tearing it all up and try some something random, not brute force exploring our way through all combinations.
Evolution seems more like building a tree where mostly all you can do is ascend the tree and add finer detail, leaving the trunk and branches (our evolutionary history) in place. It seems unlikely that, say, vertebrates are in the future going to "undo" the major evolutionary developments of the past and lose their skeleton, body symmetry, number of limbs, lungs, alimentary canal, nervous system, brain, etc. We see things like these developing in the evolutionary tree and mostly staying in place once created. Sure some fins turned to limbs, some gills to ears, but once things like that happened they seem to stay in place.
I wonder what evolution would look like if we could see it sped up from the origin of life to billions of years into the future? A building up of complexity to begin with, but those major branches of the evolutionary tree remaining pretty stable it would seem. Continual ongoing change, but of smaller and smaller scope, perhaps - building on what came before.
> It seems unlikely that, say, vertebrates are in the future going to "undo" the major evolutionary developments of the past and lose their skeleton, body symmetry, number of limbs, lungs, alimentary canal, nervous system, brain, etc. We see things like these developing in the evolutionary tree and mostly staying in place once created.
Try looking at whale skeletons over time. What isn't beneficial gets undone.
Try looking at the giraffe's recurrent laryngeal nerve. What isn't beneficial is sometimes retained as long as the cost isn't bad enough to impair reproduction.
https://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve#Evid...
What doesn't affect fitness, or has relatively little cost, can and does propagate over time. By definition, nothing is selecting against them.
Similarly, beneficial and complex traits, like eyes, can "regress" if nothing selects against that trait. Plenty of species have lost their sight, making them less generally fit for many environments, because in a certain place and time those species could reproduce even without perfect vision, or just as the result of genetic drift.
Yes, but it still seems that large scale structure tends to be preserved and it's more localized things like limbs/eyes/ears/teeth that may adapt. A chicken may have no teeth, but it's still basically a therapod.
I'm guessing there may be at least a couple of reasons for this:
1) Large scale structures evolved over long periods of time, involving layer upon layer of genetic change. This isn't going to be undone quickly or by any localized change, and those rare cases where a genetic change/defect does impact some fundamental aspect of the body plan (e.g. a frog with six legs) are very unlikely to be successful.
2) It seems possible that evolution acts to preserve large scale structure that has proved itself over time, and changes to which tend to be detrimental. In the same way that sexual reproduction seems like an evolution hack to evolve faster, then perhaps animals have also evolved genetic hacks to preserve/stabilize large scale structures that are critical to survival.
>>> It seems unlikely that, say, vertebrates are in the future going to "undo" the major evolutionary developments of the past and lose their skeleton, body symmetry, number of limbs
> but it still seems that large scale structure tends to be preserved and it's more localized things like limbs/eyes/ears/teeth that may adapt
Make up your mind.
Large scale vs localized. They are not the same thing.
"Unlikely" events happen nonetheless. Viruses and barnacles are examples of discarding structures, and it could possibly happen in some vertebrates.
In a billion years, the sun's intensity would have increased such that life and the Earth itself will look very different, assuming life can adapt to living on basically a different planet. There might not be oceans left by then.
When the environment changes sufficiently to wipe out whole branches of the evolutionary tree, I'd still expect those branches still alive to evolve in incremental fashion. Even if most lineages were wiped out, leaving only extremophiles, then those would still be building upon their own evolutionary history.
I assume we will have sterilizing temperatures and pressures on Earth if all of the water ends up in the atmosphere, and heat releases even more greenhouse gases + subterranean water, leading to a runaway situation like Venus or worse.
Maybe eventually, but I'm not sure of the relevance to the discussion, which is about the incremental nature of evolution.
Point is the Earth might reach a state that even incremental evolution can't overcome, my response is to your question about what life might look like if we sped up by billions of years. It might not look like anything.