If I had to choose three adjectives to describe Darwin’s theory of evolution by natural selection, they would be:
Yes, simple. Although evolutionary biologists now know that forces other than natural selection (e.g. genetic drift and gene flow) can cause populations to evolve, Darwin’s theory still provides the basic framework for understanding the history of life, and explains much of the variation we see on our planet. And it does it with just three premises (hence my simplicity claim). Any student who passes through my Introductory Biological Anthropology course can recite them for you:
1. Individuals in a population vary
2. Variation is heritable
3. Because of this variation, certain individuals are able to survive and reproduce more successfully in a given environment than others.
That’s it. Those three premises are all that is required to understand the idea of evolution by natural selection. So why is there so much confusion and misunderstanding surrounding Darwin’s ideas? Why, during last year’s celebration of the 200th anniversary of Darwin’s birth and the 150th anniversary of the publication of On the Origin of Species, did a poll reveal that only 4 out of 10 Americans believe in evolution?
The ongoing evolution vs. creationism/intelligent design battle aptly demonstrates that religious background plays a significant role. But in some cases, people may not believe in evolution by natural selection because they don’t understand the process. Many misconceptions abound simply because people haven’t been properly introduced to the Darwinian basics.
So in the spirit of defending evolutionary thought, I want to share a few clarifications that I have found useful when introducing students to Darwin’s theory of evolution by natural selection.
- The third premise — that because traits vary, certain individuals are able to survive and reproduce more successfully in a given environment than others — is often abbreviated to “Survival of the Fittest.” But this shorthand only works if people understand that the term “fit” is relative. Individuals that are highly fit (i.e. able to produce many offspring) under one set of environmental circumstances are not necessarily the “fittest” under different conditions. In other words, changes in an organism’s habitat can turn underdogs into winners and vice versa. This is key. Remember it.
- Natural selection and Evolution are not terms that can be interchanged at will. As I tell my students, natural selection is a process that affects individuals, but it is populations that evolve as fitter individuals reproduce more successfully and pass on beneficial trait variations.
A quick example: Among a population of tree frogs, bright red individuals who are more visible against the green backdrop may be subject to higher predation and die before they reproduce. As a result, fewer “red color” genes will be passed on to subsequent generations and over time the population will have higher frequencies of the beneficial-for-camouflage “green color” genes.
- Humans (aka Homo sapiens) are not the pinnacle of evolution. In fact, there is no pinnacle of evolution, because natural selection is not a unidirectional process in which organisms become “better” in an absolute sense (see the above point about underdogs). Humans are simply the most recently evolved members of one particular primate lineage. And, despite what many of my students think, most experts agree that we are still evolving.
That’s the end of today’s lesson. Now go and explain these premises to everyone you know and maybe, just maybe, we can top 50% in the next Gallup poll.