I think a good place to start is with TIME. Oftentimes people are unclear on timescale. I know I was about a lot of things before I started really studying this stuff. I still sometimes need to check Wikipedia real quick when I read about a new finding. We might as well start at the beginning to put everything in perspective. The Very Beginning. I mean, why not?
|Age of the universe||13.7 billion years|
|Age of Earth||4.5 billion years|
|First appearance of mammals||200 million years|
|Extinction of dinosaurs||65 million years|
|Beginning of evolution of proto-humans
(Our last common ancestor with chimps and bonobos. Coincides with bipedality; see last post.)
|5 to 7 million years|
|Beginning of evolution of Neandertals||250 thousand years
(to about 40 thousand years)
|Beginning of evolution of Homo sapiens||200 thousand years|
(Update: future post about this)
|10 to 15 thousand years|
|Great Pyramid of Giza built||4 thousand years|
So now it should be easier to appreciate where the Neandertals land on this timescale. Notice anything about that time frame? Yup, the Neandertals lived at the same time as us. Oh right, let’s clear up a common misconception first. We did not evolve from Neandertals, we evolved separately. This is one of the reasons they are so fascinating to me. Another species evolving along a separate path simply cannot happen in the world we live in now for the simple fact that there are really no population groups that are separate enough for long enough – known as reproductive isolation – for that to happen. But it certainly could happen in the future – say when we populate other planets. That’s a recipe for speciation right there. But before we get too far off into sci-fi land, let’s get back to the Neandertals and us.
Anyway, I hope this timeline helps put things in perspective. It shows that yes, Neandertals lived “a long time ago,” but looked at in the larger scale of human evolution, it was not really that long ago.
Africa is where it all began, the cradle of all humanity, where the last common ancestor between us and chimpanzees/bonobos came from. While Homo sapiens were evolving in Africa from Homo heidelbergensis, some Homo heidelbergensis groups moved out of Africa and into the Near East and then into Europe (one perfectly reasonable speculation is that they were just following game). They became isolated – possibly by a glacier or other environmental factors – and reproductive isolation happened. (This map shows the Neandertal’s range.) Short term isolation happens all the time with small populations, and can be the reason certain population groups are prone to certain genetic diseases or share certain physical features. When a population is isolated for a long period (we’re talking about 100,000 years or so in this case) and especially when environmental pressures come into play, a new species can evolve.
So what makes Neandertals, or any animal for that matter, a different species? This is not always as clear-cut as you might think, and paleoanthropologists argue about how to categorize fossil humans quite a lot. One definition is that interbreeding between the two species is unsuccessful, either because it is physically impossible (the sexual organs just don’t fit together), or it is possible but does not result in successful offspring (the infant dies, is sterile as an adult, or the hybridized traits make it poorly adapted to its environment). Another definition is two species that are separated by a physical boundary (a mountain range) or by behavior. An example of separation by behavior would be a species that hunts during the day and sleeps at night, contrasted with another species that hunts at night and sleeps during the day. These two species would never interact, and therefore would never breed with each other. Speciation – the evolution of a new species – starts with reproductive isolation, resulting in genetic drift. Environmental pressure often contributes to speciation, but it doesn’t have to. Genetic drift is an interesting concept. It is known in statistics as a sampling error. You have a bowl of jelly beans, let’s say. There are 20 green, 20 red and 10 yellow jelly beans. You randomly choose a handful of ten. You should have twice as many green and red as yellow, right? But instead of you have 4 yellow, 4 green and only 2 red, because you grabbed them at random. That is sampling error. And when there is reproductive isolation, there is going to be sampling error. That means certain traits will become exaggerated and others will diminish over time. Another way genetic drift can happen is a population bottleneck. This happens when a catastrophe causes the population to crash to a small percentage of its previous size, say through a sudden or prolonged catastrophic event – disease, drought, disappearance of a food source, conflict with another group. In other words, it is also reproductive isolation, except the separation from other members of the original group is through death. Yeah I know, a lot of this stuff is pretty tragic when you stop and think about it, which I’ve done. Soul-searching posts about that are upcoming. But for now let’s continue with this group evolving in the Near East and Europe, who are becoming the Neandertals.
Oh wait – let’s not. This post is already plenty long! A blog is not a term paper, thank god, so it looks like there will be more than one post introducing you to the Neandertals. Well why shouldn’t there be? They certainly deserve our consideration for more than a few paragraphs. Coming up: now that we know the where, when and how of their evolution, who were they exactly? What were they like? There’s a lot we don’t know. But there’s also quite a bit we DO know, and I can’t wait to share that with you next time!