Those in agreement, those with a bone, and devil's advocates who can keep my logic pure are all welcome!
As with any communication attempt, agreement on a definition of terms is helpful. To begin, I figure I could provide some biological definitions of common words in this debate. I bet you'll notice right away that the scientific definitions used in the Modern Evolutionary Synthesis can be quite different than the common usage of the same words among the American public.
Evolution
Generally means "change over time," but specifically refers to a change in the proportion of a particular version of a gene in a given population between one generation and the next.
So if rat eye color depended on only 1 gene, and if I took a group of 50 red-eyed rats and 50 blue-eyed rats and bred them, then counted the reds/blues in the offspring... the percentage change from 50/50 to whatever the result would be called "evolution." If there was no change, you would say that eye color did not evolve in that generation.
Natural Selection
Charles Darwin was the one credited for the theory of evolution by natural selection. Before him, scientists agreed that life forms evolved, but they didn't know just how they did it, or what forces were acting on their changes.
Darwin outlined 4 prerequisites that have to be in play in order for natural selection to act on a population of creatures and result in evolution:
- Individals within the population must vary (no clones allowed)
- At least some of this variation has to be heritable and passed on to offspring
- Not all the offspring can survive, due to resource limitation/predation/whatever
- Individuals that are the most "fit" are more likely to survive and reproduce, passing on their more adaptive traits to their offspring
Like any scientific theory, natural selection is falsifiable, which means that it is possible to disprove it. One example that Darwin himself suggested: if you ever found an organ in a creature which benefited another species (instead of the species the organ existed in), evolution would be occuring without natural selection. Natural selection requires evolution to act in the interest of the species it is acting on.
Fitness
Fitness is an attempt to measure how well adapted an individual is to their environment. This is approximated by looking at how many offspring are produced by an individual over their lifetime. There are several different models, but the most common ones take into account differences in gender and genotype (a definition for another day) among a species. It's usually compared to an average, and sometimes looks at multiple generations of offspring (children, grandchildren, great-grandchildren, etc.).
Adaptation is a term used to describe evolution that increases an individual's fitness.
Mutation
Genetic material (i.e., DNA), can be changed in many ways. Copying errors during cell division, exposure to radiation or certain chemicals/viruses, etc. These changes to the genetic code are called mutations, but they can be good, bad, or neutral to the organism. Bad mutations are eliminated over time by natural selection because they lower an individual's fitness. Neutral mutations don't do anything, and so natural selection doesn't act on them. Good mutations are retained because an individual's fitness would be increased, they would have more children and pass on the good mutation to them, and so on.
Well that's enough for now. We can spin off topics from this or further clarify definitions if there is enough interest. Comments, anyone?
4 comments:
That's a lot to write about. Evolution? Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. That's a good topic. Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. My college education isn't good. Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. Annoying.... i know. to be honest, i don't know much about this stuff. So, I am going to keep thinking... hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. Ok, I'm done.
It's never too late to learn. And on top of that, it's really important for our society.
I feel like I should say something here, but I gots nothing. Well that's a good high level description. Truthfully I didn't hear about evolution being change over time. Maybe I'm just stupid. Yup, that's it. :( Your example of eye colors in rats didn't strike me as a good example of evolution. I always thought as evolution where something becomes better over time. Why would the eye color make things better? hah again, my stupidity astounds me. See, this is why I shouldn't be allowed to comment. Eye color could lead to better fitness, selection. Or it could not...Alright, that's nough.
No you're not stupid! I wouldn't say creationists are necesaily stupid either... :) It's just a matter of how informed you are on a particular topic.
But you brought up a great point. This is a very common misconception of what evolution is, among proponents and opponents alike. Evolution isn't always adaptive. You can have a change in gene frequency or proportion that is due to random chance, for example. Something we often call genetic drift, just random gene fluctuations.
Natural selection, in contrast, is the adaptive force. It doesn't kill off the good gene carriers, but the ones with bad genes. In that sense, it is adaptive and acting on the population in a way you might call "better."
Another common misconception is that organisms evolve to great complexity or "superiority" over time. This is not always the case -- sometimes it is more adaptive to be LESS complex. For example, it might just happen that a species that grows a big flashy tail feather to attract mates might be replaced by a variation that reduces the tail extravagance, so that more energy can be put into reproductive effort. If one has a better reproductive payoff, those suite of genes will increase in the population. It's also possible that they could co-exist with equal fitness.
You're right in assuming that most things we observe must have been adaptive in the past however. In my rat eye color example, if we observed this naturally we might ask if the eye color WAS beneficial somehow.
Ok enough rambling from me. See, you can just get me going pretty easily! :) Thanks for the comments, keep them coming! :)
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