Happy Birthday, Darwin!

This week marks the 200th birthday of Charles Darwin, a man who in my opinion, holds a rightful place alongside Galileo, Copernicus, Newton and Einstein. Darwin's theory of evolution is one of the great intellectual revolutions of human history, drastically changing our perception of the world and of our place in it. 

Given its importance, it's hard to believe how little most  science teachers spend on evolution (I have a PhD in biology and I can tell you that most of my teachers/professors skimmed over it), I thought Darwin's birthday would be a good occasion for a brief lesson.

Darwin's theory of evolution has four main parts:

1. Organisms have changed over time, and the ones living today are different from those that lived in the past. The world is not constant, but changing. The fossil and genomic record provide ample evidence for this.
2. All organisms are derived from common ancestors by a process of branching. Over time, populations split into different species, which are related because they are descended from a common ancestor. Thus, if one goes far enough back in time, any pair of organisms has a common ancestor. This explained the similarities of organisms that were classified together -- they were similar because of shared traits inherited from their common ancestor. It also explained why similar species tended to occur in the same geographic region.
3. Change is gradual and slow, taking place over billions of years. 
4. The mechanism of evolutionary change was natural selection. This was the most important and revolutionary part of Darwin's theory.

Don't remember what natural selection is? Let me briefly explain:

Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common, due to differential reproduction of individuals in a population. 

Let's take giraffes as an example. Today's giraffes have longer necks (a heritable trait) than their ancestors (see pic above) because over the millenia the giraffes with longer necks (in a population of giraffes with necks of slightly different lengths--not unlike the variation in height in humans) were more successful than shorter neck giraffes in getting food (leaves from high branches). These longer necked giraffes would therefore be less likely to starve and more likely to reproduce, passing their long neck genes to their offspring. Over time, the average neck length of giraffes increased.

There are many, many other examples and the fossil and DNA evidence supporting evolution is simply overwhelming. Of course, you wouldn't know this if you asked the American public. According to Gallup poll this week, only 39% of Americans say they "believe in the theory of evolution," while a quarter say they do not believe in the theory, and another 36% don't have an opinion either way. Way sad, especially when one considers how beautiful this idea is. Think about it: We humans evolved from lower apes, which evolved from lower mammals, which evolved from reptiles, which evolved from fish, who evolved from lower multicellular organisms, which evolved from bacteria. 

As another great biologist Theodosius Dobzhansky famously, and correctly, said, "Nothing in biology makes sense except in the light of evolution." Indeed.

By the way, if you want to learn more about evolution, check this out.