Science Sundays: What is punctuated equilibrium?

By: Meradeth Houston on 7:00 AM

Welcome back to Science Sunday! If you haven't had a chance to enter my giveaway, hop over and do that really quick, okay? Trust me, you won't regret it!

So, today, I thought I'd talk about a part of evolutionary theory that's always, always getting messed up on TV and movies. This is punctuated equilibrium, which is basically when evolution speeds up during a period of time, creating change at a rate that was faster than what had previously been seen.

Here's the thing about evolution (which at its most basic is just change over time--species and traits slowly change over time) is that there are a few things about it which are very interesting. What I'm dealing with here is the fact that the pace of change (evolution) can change. During times when a species is existing in a stable environment that it's well suited to, and no new adaptations have arisen due to chance, then a species may sit in stasis and not change a whole lot over long periods of time. Think about the alligator as a good example: that species hasn't changed much in ages!

But, there will be times when something will shift in the environment, or a new really beneficial mutation will randomly come along, and a species will change really fast. This happened in our human ancestor's brain size: the brain size remained small--not much bigger than chimps--for a very long time after the human lineage split with our closest relative. But about 1.8 million years ago we see a dramatic shift in brain size, a jump to a size that while not the same as ours, was still much larger than a chimps.

Do keep in mind that these rapid periods of change don't forgo the basics of how evolution works. It's just a faster process from time to time. So, something kicks of a change in the population (this is most likely going to be a change in the environment), and only those with a certain trait survive. They then pass along the trait that allowed them to survive to their offspring, and suddenly the population looks different in this new generation as there are more of the genes that were beneficial that were passed along. If this process is fast, or severe (so lots of individuals without the trait) die, then it can look like really a really fast change. The underlying process is no different from a gradual shift though.

This last part is what I always see getting mixed up, where shows think that very rapid evolution means they can skip over the randomness of a new mutation arising, or the process of it coming to high frequency in a population. Le sigh. I tend to yell at a lot of fictional characters....

So, tell me what you think? Does that make some kind of sense?