Is the Science Ever Settled? Theories, Hypotheses, and What Science Really Does
A struggle for survival: I think this one is pretty obvious, but let’s think about why it’s obvious.
Anyone with an outdoor cat will eventually see evidence that some birds or field mice or lizards lost their struggle for survival. But how can we falsify the assertion that there is no struggle for survival? Well, we’d expect to see a lot of animals who die peacefully of old age; instead, we see predation and disease. So, the more times we look for peaceful chipmunks dying in bed surrounded by loving family and friendly neighbors, and don’t find them, the more we are confident that “nature red in tooth and claw” is the way to bet.
That one is easy, but that’s why it makes a good first example. We’re already quite used to the notion that other things die in order for some to survive as we eat our corned-beef sandwich. But now let’s look at the other inferences.
Individuals less suited to the environment are less likely to survive and less likely to reproduce: This one is just on the edge of being circular, because the definition of being suited to the environment is that you survive and reproduce. So, let’s look at it with an analogy.
Let’s say we have a thousand coins. I’d use silver dollars, but they’re hard to find, and I’d use quarters, but this is a low-budget experiment: let’s assume a thousand pennies. We set up some kind of machine that can flip all the pennies simultaneously, and we declare that each penny is one individual of some species. If the coin comes up tails, it’s dead, and we remove it from the game.
Flip once, there are roughly 500 left (Usually. There’s a whole ’nother column needed to talk about the Gambler’s Ruin and why this is only an approximate statement.) Flip twice, and there are 250 left, and so on.
But now, let’s slip in some ringers, unfair coins: some always come up heads, some always come up tails. Flip the pennies once, and all the tails-up ringers die, along with half the fair coins. Eventually, if you flip the coins long enough, there will be nothing left but the all-heads ringers. That’s natural selection.
Now, let’s add a bit to our analogy. After each flip we make exact duplicates of the pennies that came up heads -- the ones that didn’t die -- enough to fill in the board so we always come back to 1000 pennies.
Flip again, and half the fair pennies survive, but all the duplicate all-heads ringer pennies survive. The longer this goes on, the more ringers there are, until after some length of time you have all pennies that always come up heads. (Strictly mathematically, you can’t be positive the fair pennies will ever be eliminated; the probability is always greater than zero that there’s at least one survivor. But thats certainly the way to bet.)
However, notice something: this happened entirely because we arbitrarily chose that a coin that comes up heads survives, and the others die. If we’d made the opposite decision, the all-tails pennies would have been better suited to their environment, and eventually all the pennies would be all-tails pennies.
The final inference:
This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species.
Our same little penny-flipping machine shows us exactly that: eventually the population of mixed all-heads, all-tails, and fair pennies becomes a population of all-heads. The fair pennies become extinct. (I’ll leave it as an exercise to figure out where the original all-heads pennies came from.) The population has “evolved” until it’s more fit for an environment in which coming up tails means death.
We shouldn’t reason too much from analogy, though; we ought to see if we can bring this back to real life, which gets complicated, because the idea of a “species” is more slippery than you’d think.