I am preparing for the transition to full time teaching and the jump to light speed that is involved in teaching a subject for the first time. I find the light speed jump is eased somewhat by actually reading the textbook and taking notes, even though the annoying PhD part of my brain keeps spoiling the plot by completing the sentences before I finish reading them. Sometimes though, that PhD part of my brain is wrong, and thats a big reason why I teach. I also think better if I can either talk or walk, or talk and walk. Since typing is a form of speech these days, I am probably going to be subjecting both readers (thanks Pete and whoever that other person is!) of this blog to a fair amount of “thinking”. If you stumbled on this because you saw me post it on Facebook and haven’t learned that both my writing and the subjects I choose to write on are nerdy and boring to all some most people (except Pete and that other person!), well, I just warned you.
Evolution is a really big thing when you are teaching Biology, both because it so obviously ties all life (I do mean all there) together and is as obvious as gravity, but also because there is quite a debate going on in our country about how we should talk about it to students. At the moment, I am thinking about a statement in the textbook I am to teach from (I am intentionally not mentioning the subject or book, it really isn’t important):
“…eventually though, evolution selected the cell as the best structural solution for supporting the fundamental characteristics of life.”
While I do believe the data suggesting that self-replicating RNAs eventually became housed within a membrane (the first cell!), this statement has a couple of big problems. First, evolution does not select anything. Evolution is a word the describes a process. Evolution is the process of something changing. A situation can evolve, a person can evolve, a hopelessly boring blog can evolve. Cooking is also a process, but cooking does not DO anything; it doesn’t select the ingredients, mix the ingredients, put the ingredients in the oven or prevent the kids from sticking their hands in the uncooked ingredients and then painting the walls with them. Cooking is the term that describes the process. Getting back to evolution, environments can select, diseases (which are technically a part of your environment) can select, even humans can select – but evolution does not. If you think I am quibbling over terms, substitute the word “God” for “Evolution” in the above quote – it fits far to well. (thin ice! thin ice! move on Jeff, move on!). Natural selection is what does the selection (and even that isn’t the only mechanism of evolution). Simply put, ANY genetically determined feature in a population of organisms that results in more or less grandchildren in that population will over time result in that feature becoming more or less common in the individuals of that population. Longer arms, shorter arms, extra arms, baldness, blue eyes, green eyes, one eyes – if even one individual in a population has one of these features (and the feature is genetically determined) and the feature affects, even indirectly, their ability to have babies, its a good bet that in a million years either everyone or no one in the population will have it. Natural selection baby,
along with genetic drift and gene flow its how our eyes got moved to the front of our skulls, its how we started walking upright and lost our tails. [after more conversation and thought, I now think that NS is the probably the only mechanism that can produce changes such as this].
Second, to say that evolution results in the selection of “the best” anything is dangerously close to being flat wrong. The misconception that evolution results in better and better solutions is extremely common when students walk into my classrooms (hopefully less so when they walk out), and its something that is far more problematic than than saying “evolution selected for a better phrase in this paragraph”. To put it flatly, evolution not only doesn’t necessarily result in the best solution to a problem, like government work – “good enough” is all it can do. Literally. As a thought experiment, imagine a population of cheetahs and a population of penguins living in the African savanah. The penguins obviously can not defend themselves well against the cheetahs (unless one of them is born with a claw on their wing (happens in other birds) and that armed penguin (there’s a pun there) successfully breeds) so they must run. Imagine that these penguins can run fast, fast enough that 50% can outrun the cheetahs. Now imagine that 10% of the penguins are faster runners (more fast twitch muscles, it happens in other species) and over millions of years, that 10% tends to get eaten less frequently, so the average speed of this penguin population increases. For slower cheetahs, this could be the end. As the average speed of the slowest penguin herd surpasses the top speed of the slowest cheetah, well, cheetah eats less, cheetah has less babies. Over time, the cheetah herd’s average speed could increase as well. But here is the important point: natural selection does not select the fastest cheetah – as long as a cheetah is fast enough to catch enough penguins so that it can have rock hard abs and impress the cheetah ladies, its fine.
Need a more concrete example? Ok, off the top of my head, I pick male pattern baldness. Given the amount of money spent* on keeping a man’s coiffure thick and luxurious, you would think that MPB (which is genetically determined), if given millions of years would gradually recede from the population. However, my two healthy children at home give me a concrete reason to doubt that.
*Extra bonus points: how long would it take all of these creams, gels and plugs to remove male pattern baldness from the human population? Assume that every male thinks this is important.