Imagine Earth ten million years from now. Or eighty million years. The continents will have shifted from their current positions. New landmasses will be formed, along with new mountain ranges. These will in turn change weather patterns, meaning that the sorts of plants and animals that can live on these land masses will also be altered. Given that we can extrapolate the positions of continents far into the future based upon what we know of their movements now, we can also make educated inferences about the climate, and by extension the sorts of flora and fauna that will inhabit the Earth. But it’s a mistake to think that we can know this in any great detail. We can make broad sorts of predictions, like “this region will be inhabited by plants with high water retention or capture rates, by virtue of the arid conditions that will prevail in this area” or “this region will have animals that will use sound to call out for mates, given that rain forests are dense with vegetation and visibility is hence limited”. But these aren’t really the kinds of predictions that would necessarily spark the imagination of the general public. They’d be more interested in predictions that tell us about the specific sorts of organisms in the future, like “in ten million years, there will be a shark larger than a whale that jumps up into the air to catch giant birds before crashing down onto the water.” These sorts of predictions really are too detailed to make with any confidence at all, because evolution has a large component of what’s known as “stochasticity”, or randomness. While there is debate over the extent of this stochasticity – namely, whether evolution is more like the weather or more like a machine – it cannot be doubted that purely random factors play an enormously important part in the history of life. Small differences in initial conditions can have profound ramifications for later routes taken by evolution, and there are plenty of other quirks and unpredictable factors that play out all the time throughout the history of a lineage. There is, nevertheless, a strong component of regularity, and this is manifested in natural selection. There is also the potential for an interesting and subtle interplay between contingency and regularity. For example, suppose that a meteorite happens to strike the Earth and precipitates a mass extinction. What might we be able to say about the importance of this event? It depends. Some lineages might already be doing badly anyway, and hence already be on the way out. A mass extinction could finish this group off by making the environment that much more difficult to navigate. On the other hand, the group that’s doing badly might happen to have features about it that confer some advantage during these events. And you can think of variations on these basic themes. Or extinctions might be essentially random events, that have pretty much the same chance of ending off any one group as any other. I suppose that the degree of selectivity as opposed to randomness has to depend on the nature of the mass extinction event itself. But the take home message is that evolution is going to depend on many factors, at the local level and more broadly, and the interplay between the processes taking place at these levels. You can now see why any detailed predictions are going to be sketchy at best, and almost certainly wrong.

Throughout life’s history, we have seen that there are certain “themes” that play themselves out again and again. Before the Permian mass extinction (which wiped out some 90-95 percent of all the species on Earth), there were herbivorous creatures being hunted by ferocious carnivores. During the Mesozoic Era, dinosaurs filled these niches, and now in the Cenozoic Era we see gazelles, buffalo, lions and leopards. All over the place, down through the geological strata, we see that lifeforms have adapted to their environments, often reproducing remarkably similar traits in groups that are only distantly related. This independent hiting-upon of similar design solutions to similar sorts of problems is known as “convergent evoluton”. It’s as though life “finds” these solutions over and over again because they represent good ways of doing a job; natural selection finds them easy to produce because they represent the path of least resistance, as it were. We can therefore be confident that life in the future will continue to make use of these themes. There will continue to be herbivores grazing on the open plains, being hunted by predators. We don’t know what they’ll look like, but  again, we can surmise what sorts of traits they’ll likely have, and even what sorts of behaviours they may exhibit in order to be good at carrying out these lifestyles. If we know something about the groups that are doing badly today, we might even flesh out a bit of detail by saying not only what sorts of traits the organisms will have, but in what groups they’ll be expressed. For example, if we have reason to think that mammals are going to do badly (based on trends leading up to the present time that we think will continue for whatever reason), we could say that this region of the Earth will likely be inhabited by, say, reptilian carnivores. It could well be that we’ll see reptiles not unlike the dinosaurs, blossoming into a second “Age of the Reptiles”. It’s possible (and I’d rather like to think it will happen this way).

But I think it’s safe to say that, a) as long as keep to the rules of natural selection, your guess is as good as mine, b) anything we predict is likely to be nowehere near as weird and wonderful as what does end up evolving (just think of the strange animals that live on Earth today. Who could have predicted, living back in the Devonian, that there would be something like a rhinoceros or a giraffe many millions of years hence?) and c) we just don’t know, owing to the (potentially) massively contingeny nature of evolution. It’s fascinating to think about. I have no doubt that the more we learn about the past, the better will be our ability to make predictions about the future (even if we can’t really test these ideas, given that we may not be around long enough to see them vindicated or falsified).

Anyway, check out this website, based on the television series “The Future is Wild”, which postulated all sorts of bizarre (to us) creatures. My favourite is the “flish”, a fish that has evolved the ability to sustain powered flight and lives as an air-breather, filling the niche that birds do today.