Have you ever wondered about the origins of humanity? Most people generally understand the idea of evolution and that people used to resemble our ape and monkey cousins more closely than we do now. But, to quote one of our readers who recently posted on the Sketchy Science Facebook page, if people evolved from monkeys “how come we still got monkeys?” To answer that question, we turn to one of the greatest scientists of all time. Mr. Charles Darwin.
Evolution is built on three basic ideas:
1) It is possible for the DNA of an organism to change over time. A more scientific term for this change is ‘mutation.’
2) Mutations can either be helpful, harmful, or do nothing in terms of an animal’s survival.
3) Over time mutations accumulate and produce new species.
As we saw in the mitosis article a while back, cells replicate like crazy but every once in a while they make a mistake. Sometimes those mistakes happen at the level of DNA and lead to some change in the organism. If that change is something like a piece of inactive DNA getting a little bit shorter, that won’t really effect the life of the animal all that much. If, on the other hand, that change is something like a third arm or the ability to shoot lasers from one’s eyes, the environment might take notice.
It is the environment taking notice that drives evolution. This is called “natural selection.” If your third arm is super strong and helps you survive more effectively, you might live to have three-armed offspring. If your third arm just gets in the way and can’t do much, it might get caught up in some bushes while you are running from a lion. No freaky offspring for you. Over time, changes in a group of animals build up if they are helpful (or neutral) and can become the norm. Get enough changes built up, and the new animals might be so different from the old ones that they could be called a new species.
That’s all well and good, but it doesn’t answer the specific question posed in the title of this article. To understand that, we have to clarify something: No species that exists today evolved from anything else that is currently alive.
When scientists say that humans evolved from apes (or monkeys if you go back far enough), what they mean is that modern humans and modern monkeys share an ancestor. That’s kind of a tricky thought so let’s consider an example to help explain speciation (the evolution of new species):
Imagine a group of monkeys living in a valley. They have all the bananas they could want and enough room to throw their feces as far as their arms can manage. It’s monkey heaven. However, all good things must come to an end and one day a massive landslide cuts the population of monkeys into 2 groups. Now let’s imagine those groups don’t interact again for another few million years. They build up their own mutations and adaptations and split up on the evolutionary tree. If you waited long enough and then removed the barrier between them, you would have 2 totally separate species. One may have changed a lot, the other might have only a few slightly noticeable changes, but neither is the same as the original animals that lived in monkey heaven.
Sometimes species can go a really, really, ridiculously long time and change very little. Crocodiles have existed in pretty much the same form since the dinosaurs were worrying about being late for work, something like 240 million years ago. Humans have only looked like we do now for about 150,000 years. We were tree-swinging, feces-chuckers somewhere between 5 or 6 million years ago.
These different rates of change are why sometimes we hear people say things like “Humans evolved from monkeys.” We didn’t. That’s impossible unless you managed to freeze our monkey-like ancestors and thawed them out a few million years later, still alive. What those people mean is that monkeys look more like the common ancestor that we share with them than we do.
So, how come we still got monkeys? The reason is that monkeys haven’t had to change as much as we have to survive over the past several million years. The monkeys you see today aren’t the ones we evolved from, they just have more of a family resemblance.