Field of Science

Are we doomed?

#SciDoom New Statesman posed the question "Are we doomed?" to a bunch of prominent scientists, but we are all game.



Yes, of course we are. Let me count the ways.

I can think of at least seven "levels" at which we could be doomed, and out of those, three are certain but long term, while the rest are less certain but short term: universe, solar system, planet, life, humans, civilization, economy.

The first three are bound to cease to exist, and this is known with certainty. The universe will keep expanding and cooling until the temperature is the same everywhere (wiki). Fortunately this will take a little while. Sooner than that will be the end of out dear sun (5-10 billion years) and with it the Earth.

But life on Earth might be destroyed long before that. A nice gamma-ray burst or a cool meteor shower could annihilate all life on the planet. And much sooner than that we might see humans going extinct for a plethora of reasons. Civilization may cease to exist for a number of reasons, and our economic system may indeed be doomed, which is what I think many people concerns themselves with than any other of those seven levels.

Wearing my evolutionary biologist hat, I worry that we humans as a species are doomed much sooner that I'd like. As much as I can feel disgust in our many greedy ways, I also love so many of the things we do, and would be really sad if we all were to disappear. And yet, I think that is likely to happen. The evolutionary processes that I would credit with this would be bottlenecking, genetic drift, and natural selection. In that order.

For whatever reason, it is likely that the human population will be decimated some time in the future, perhaps even as soon as within the next hundred years. A cataclysmic event caused by global climate change, perhaps?

If anyone survives at all, I predict it will be in a number of smaller populations separated from each other geographically. These lucky few will thus pass through a genetic bottleneck, which will reduce both the effective population size and the genetic variation within each population. Such a surviving population will eventually bounce back and start growing again, and as it does, the genetic idiosyncrasies of each population will be retained, because the isolation of the surviving populations will make them unable to mate with each other and reduce the variation between the populations. Rather, the genetic variation between the different populations will be amplified, since each population is small. Small populations are more affected by genetic drift - the random sampling of genes (alleles, actually) - and so the population will evolve by drift through the generations. Eventually some populations will grow in size, and intra-population variation in fitness will start to matter again. This is because genetic drift is less effective in large populations, just as throwing ten thousand 7-sided dice will give you an average closer to 4 than using only ten dice will (incidentally, I just did that and got 3.9954 and 2.6000, thus proving my point and that evolution is true, no less). The population thus transitions from being at the mercy of genetic drift to being ruled by natural selection.

Natural selection has the same effect as drift, namely to decrease the variation within a population, while it will increase variation between populations. At least this is true if it holds true that the selection pressure isn't similar among the populations. If the environment is different for the different populations, then natural selection will push the populations to evolve differently. This will then result in a number of small, distinct populations evolving independently, each responding to the various selection pressures that the environment subjects them to. A small group of people in Hokkaido surviving a global cataclysmic event that also wipes out the amenities of civilization, will perhaps be selected for being short and stocky to keep warm, while the few survivors on New Guinea will go through rounds of selection (read: die-offs) due to diseases that they eventually will evolve resistance to. Et cetera.

Assuming that the environmental changes caused by the global cataclysmic event are severe enough that the separated populations won't be able to interact (i.e., have sex) for long enough, the different populations will continue to diverge from each other, and speciation will eventually occur. 6-7, say, million years hence, one of these populations will finally get the hang of it, and civilization will again rear its ugly head. The people of New New Guinea will have created technology and science, and because they are no less curious than their ancestral fools who caused the cataclysmic event in the first place, they will eventually figure out their own origins. Among other things they will find that they are closely related to another humanoid species native to Hokkaido - a species with a very different morphology form their own tall'n'handsome physique. Paleontologists will discover that their last common ancestor were a species of humanoid somewhat shorter than themselves, with smaller heads and no tail, not unlike the Hokkaido species.

With new techniques to decipher ancient DNA found at Antarctica, in addition to historical records unearthed in a bunker in the northern hemisphere, New New Guinean scientists eventually deduce that all living New New Guineans can trace their Y-chromosome back to one male from approximately 6.2833 millions years ago. This man had two offspring, both males, who happened to be separated from each other when the cataclysmic event devastated most of the human population of about 7 billion individuals. One of those was in Hokkaido, and the other was in New Guinea. He was, even without a tail, quite tall’n’handsome himself, and more than just quite proud of both his very successful sons.



This was a story of one way of human doom. Following a world-wide cataclysmic catastrophe, most of us will leave no descendants. A few of us will, and if fate will it, those descendants will split into two species (in this case via allopatric speciation). This may not sound much like doom, but humans in our present form will cease to exist, replaced by other species quite unlike our present selves. A beautiful doom, but doom for us nonetheless.

Did I answer the question "are we doomed?" I'm not sure I understood it in the first place, but this is what came out.

4 comments:

  1. Always fun to think about this stuff... The time scales are just so vast, it's hard to even think about what that would be like. And since we know pretty much for certain by this point that we are the first instance of civilization on this planet, we don't have any data points from which to generalize... heh...

    For instance, I might argue on one hand that you won't have the two descendant species co-existing, because we'd expect to see something like what apparently happened in our history, with all the other Homo species/subspecies going extinct, presumably from competition with us. On the other hand, I could argue that that (possible) extermination took place when we were not quite behaviorally modern, and that behaviorally modern humans would have acted better. Or maybe not. We have no data on which to base our conclusions, only guesses! Which I guess is what makes it fun :)

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  2. I love the artwork. The boy shows promise :)

    The history of two humanoid species co-existing for any length of time is not great. It would probably happen that the two groups would meet before becoming fully divergent. Then some of the less fussy members would breed - as some of our European ancestors did with Neanderthals :o

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  3. Yes, that is likely. Assume here that some fortuitous set of mutations make hybrids of the two populations much less fit after not such a long time. Also imagine that the cataclysmic event is so severe that the two populations don't overlap for a long time. After all, we know that speciation does happen this way.

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