Every individual organism that ever lived, except those alive right now, has died. And every species of the multicellular organisms, at least, except the ones currently alive have gone extinct. It should therefore be uncontroversial to say that the species Homo sapiens will go extinct. Even so, I suspect the majority of people belonging to this species would not believe that possible even when they know no one lives forever. Well, it is tough to contemplate your own death. You do it because you imagine your children or others you care about will still be here to think about you. It's a little different to think about extinction. It seems more frightening to consider a world where there will be no one around to care about anything.
When confronted with the inevitability of species extinction applied to our kind most of us will naturally look at our cleverness and assume we have the ability to persist endlessly. How often have you heard someone proclaim that evolution doesn't apply to us anymore because we have technology. The near-sighted can still hunt because we have glasses. But there is now ample evidence that rather than us rising above mere biological evolution, that our species has been evolving, and possibly at an accelerated clip. But we need to be careful here. We've found quite a lot of evidence for micro-evolution, subtle shifts in the frequencies of alleles that are under selection pressures. I have half jokingly suggested that assortative mating, for example, is underlying what appears to be a divergence between political progressives and political conservatives. Look at how the Congress works today (or rather doesn't work) and you would have to admit the divergence is real enough. Birds of a feather not only flock together they tend to mate within their flock (statistically speaking of course). Blue states, red states.
Micro-evolution can work at a pretty fast pace when the selection pressures are high. It mostly works on the diversity of alleles already in the population rather than on radical mutations. And with some mixing the effects can be masked for a while. Dominance vs. recessivity also clouds the picture. But it turns out in cases that have been well studied, e.g. Darwin's finches in the Galapagos islands, major shifts in allele frequency, with measurable anatomical or behavioral consequences in the population, can occur in tens to hundreds of generations. It doesn't take thousands of generations for a trait to take over if the selection pressures are high enough.
The working of micro-evolution creates some difficulties for defining what we mean by a “species” in the first place. For example, the usual definition of a species involves reproductive isolation, where the individuals cannot mate successfully with members of a different species, even if they look and act very similarly. As a rule this definition seems to hold up. But it isn't rigid. In systems terminology this is a “fuzzy” boundary condition (as well as a porous boundary!)
If the progressives and conservatives are truly diverging and there is a genetic basis for it, perhaps we are witnessing sympatric speciation in real time! I bring this up because, getting back to extinction, there are two basic ways a species can go extinct.
The Branches of the Phylogenetic Tree
Notice how there are many branches on the tree that just abruptly end? In reality we do not have anything like a complete picture of the full history of evolution. If we did what we would see is not a tree but a very densely branched bush. But the point is that branches do come to an end. This could either be because the species at the end are still alive (like little new growth shoots popping out around an otherwise perfectly trimmed hedge). Or, for most cases, it is because the species, or genus, or family, or... have come to the end of the line (to mix branching metaphors). One form of extinction is that the last creatures in the species dies without having produced any branches that might carry on, perhaps due to massive changes to the habitat for which the species simply couldn't adapt. That is what most people think of extinction. Think dinosaurs.
But there is an alternative. What if one species gives rise to a new species? What if there is a branching before the parent species bites the dust? The new species carries on some or even most of the traits of the parent species. They are still descendents, just different. This is actually the story of human evolution. There have been many genuses and species, even within Homo. Only one remains today, probably because as humans along the line leading to sapiens out competed those that remained. Homo neanderthalensis may have lasted many thousand years after sapiens moved out of Africa and into the Mideast, Europe, and Asia. There is even genetic evidence suggesting that cross-breeding was possible (so much for the species designations!) In the case of Homo there appear to have been several branchings with species co-existing for long periods of time. We know of three relatively recent branches, sapiens, neanderthalensis, and floresiensis. The last may have survived in isolation until as little as 13,000 years ago! The Neanderthals made it to maybe 35,000 years ago before losing out to sapiens in Europe. That would seem to leave just one Homo left and not that many Hominidae in total.
Then there is an interesting case of Homo sapiens idaltu, a more primitive form of Homo but still considered sapiens (our current version of “sub-species” is really called Homo sapiens sapiens which might make some people think we are twice as wise as our predecessors). Clearly sub-species can evolve from pre-existing species. And both sub-species can occupy the same range if there is a sympatric mechanism keeping them from inter-mating. From the picture of hominid evolution that has emerged in the last decade it appears we (hominids) are really good at doing this sort of thing.
As ever I expect the combinations of massive climate change and the loss of our exosomatic power sources are going to lead to some pretty nasty times in the near future. And that means very strong selection forces will be at work on our kind. Given that humans are now occupying almost every environment on the planet and the stochastic (chaotic) nature of climate shifts, some are bound to be located somewhere less harsh than others. Also given that we are omnivores and capable of majestic feats of affordance, I strongly feel there will be survivors. And after every previous die-off there follows a period of rapid speciation (adaptive radiation) which puts us back to how rapidly micro-evolution can occur. With so many rapidly developing niches, it seems life is absolutely exorbitant in creating new species, genuses, and so on. But we will go extinct. The question is will we have descendants in the form of new species of Homo. If so, what will they be like? How will they behave? Will they remember us?
Let's speculate a bit. I think the vast majority of people who contemplate this die-off believe that the harsh conditions will select for harsh beings. Those stuck with the “nature red in tooth and claw” vision of evolution (and believing that what Darwin gave us was the last word on evolutionary mechanisms) easily come to this conclusion. But as the evidence for the role of cooperation in evolution, and how it seems to be more strongly selected for when conditions are particularly harsh, see a different scenario playing out. No one will know for sure what will happen. But I prefer to think that should some survivors of the only extant species of Homo get through the bottleneck and be exposed to those future conditions, that they will continue evolving toward greater cooperation.
As for sympatric speciation, I do think it is already underway. If we had more time, say several hundred more generations, we would see the emergence of many incipient sub-species of our genus showing both anatomical and behavioral distinctions. If assortative mating were given a small boost, or at least an advantage, say through an Internet dating service, then it is possible we could accelerate that process somewhat. Why not? If already very cooperative-feeling people find each other more attractive then we might help evolution along! I'd like to believe small groups of highly cooperative (eusocial) people provide a head start to that future evolution.
Invariably someone thinks this is the same as eugenics and the emotional responses come out. I received a few hate e-mails from several people who had heard Mr. Emerson raise this on his Doomstead Diner pod-cast interview of me a few weeks ago. I suppose it is inevitable that people have a strong emotional reaction to any hint that their reproductive rights are somehow being threatened. But I maintain staunchly that what I am talking about is not some form of coercive mating scheme. It is simply recognizing an already existing natural process and simply applying a little grease to the skids so that good things happen before the bottleneck arrives. If I'm wrong about the occurrence of more eusapient genes in the pool and therefore we can't identify those who would become wiser as they age, then so what? I am definitely not talking about cutting off the balls of any male who doesn't have the right brain capabilities (in my opinion). For all I know I might end up suffering that fate myself. Besides that would be an awful lot of surgeries! No the point is that people who share common traits tend to match up (statistically, of course) and the suggestion is that if we did manage to identify higher sapient individuals at a young enough age, we simply introduce them to one another and let nature take its course. So please, can we cease this talk about eugenics and the nasty-grams? Just take some time to think it through.