Metaphors can be powerful teaching tools, leading us to an understanding of new concepts by connecting them to ideas we have already grasped. As with any tool, choosing the right one is important. A metaphor that builds on a familiar, evocative image but fails to capture essential details of the new concept can give a false impression of learning. It’s like using a wrench that’s too big. You turn and turn and feel like you are doing work, but at the other end nothing happens because the wrench hasn’t engaged.
Some ideas in science are learned readily, because they match our intuition of our how the world works, built from common experiences. Gravity makes sense because we’ve all jumped up and then come back down. The flow of electricity is easy to observe as lightning or a spark of static. Deciding if a baby has her mother’s eyes or her father’s smile introduces us to inherited traits.
Learning evolutionary biology presents a bigger challenge. Noticeable changes in the traits of plants and animals can take generations to develop. The full scope of evolutionary natural history spans billions of years. On the other hand, each observable change traces back to microscopic differences in cells and genes. Our intuition breaks down at scales so far from human experience. We need metaphors to help span the gap.
Unfortunately, some metaphors for evolution don’t engage with the details of the science. They persist because we can understand the point they make, and so we feel satisfied that we have learned something. But what we’ve learned has nothing to do with the actual science. Here are some popular ones that just don’t get the job done.
Tornado in a junkyard
Could a tornado working with nothing but spare parts produce a functional jetliner? Maybe in theory, but the scenario is so unlikely as to be effectively impossible. The tornado can only randomly mash parts together, and random combinations of airplane pieces almost certainly don’t fit together. Since evolution is random, can we expect it to be any better?
For starters, evolution does not begin with bits and pieces just lying around. Even if we are talking about the origin of the first living creatures—which this metaphor was originally meant to critique, by the way—scientists do not propose that life arose all at once. Instead, incremental changes in the chemistry of the early Earth eventually produced the earliest cells. And the atoms and molecules of chemistry don’t just lay around like discarded mechanical parts; they are constantly bumping into their neighbors and reacting chemically whenever possible.
The evolution of life’s diversity did not happen all at once either. Once living creatures came into existence, they continued to change, one step at a time, over many years. Individuals representing new species are not assembled from pieces; they descend from their parents and grandparents, inheriting some of their traits with some variation. Those variations may be random, but whether they stick around is not. That depends on whether they help make more children.
Monkeys banging out Shakespeare on typewriters
Let a monkey bang on a typewriter and we will probably get unintelligible sequences of letters, numbers and punctuation. Now and again, we’ll find a sequence of letters representing a familiar word. Bring in more monkeys and more typewriters and we’ll accumulate more actual words. Can we get enough monkeys and typewriters so that we get Hamlet?
Since monkey-typing appears random, it seems like a good metaphor for the randomness of evolution. A simian Shakespeare seems implausible, so maybe evolution is too—or so the thinking goes. If we do the math, an infinite troop of monkeys with infinite time actually will type all of Shakespeare’s plays. But evolution doesn’t have an infinite amount of anything to work with. So infinite monkeys don’t help us much as a metaphor for evolution.
Even a limited number of typing monkeys is limited as an evolution metaphor. Each monkey starts from a blank paper. But with evolution, each generation starts from the biology of their parents. And each generation gets feedback on whether any changes they make are improvements. When one monkey bangs out “To be or not to bd,” she has no way of knowing how close she came to the real thing, and none of her troop-mates can benefit from her success. We’d have to give our monkeys photocopiers and copy editors to get closer to how evolution actually works.
Evolving car models
Many human-made designs, for cars or smartphones or clothes, change in form and function over time. In everyday usage, evolution just means “change over time,” so in that sense cars and phones evolve. Can they teach us anything about biological evolution?
Changes in manufactured goods can illustrate some features of biology. Fitness in biology relates to reproduction; greater fitness leads to more children. Similarly, human-made design elements that attract more money and attention are reproduced in other designs. The iPhone aesthetic quickly appeared in other mobile phone designs, and safety features like anti-lock brakes become standard for cars. A biological feature that increases fitness can similarly become widespread in a population because it gets reproduced more.
At the same time, those design elements are not reproduced via lines of direct descent. They can be mixed and matched across manufacturers and product lines in a way that biological features cannot. Meanwhile, living creatures can have children, but cars cannot. So cars cannot evolve without human intervention. But living creatures have capabilities cars and phones do not, so ultimately the metaphor reaches its limit.
King of the Hill
It is easy to imagine “survival of the fittest” as a competition to find the very fittest species or individual. After all, when we want to know which team or athlete is the best, we arrange head-to-head matches and elimination tournaments. How can there be such diversity in biology if there can be only one victor who is the most fit?
At best, “survival of the fittest” is an incomplete summary of evolution, one which Darwin himself did not originally use. There is no single fittest individual or species. For one thing, living creatures of very different types can be comparably fit for very different reasons. For another, fitness depends on context, allowing many creatures to be fit for different niches. Evolution does not predict, nor does it require, that individuals or species eliminate each other to be the last one standing.
It does predict that whatever allows life to flourish will become more abundant over time. How much more abundant depends on how much it helps life to flourish. So an incremental improvement of our summary would be “survival of the fitter.” That way we emphasize the relative nature of fitness and allow for a multitude of survivors.
Some of these metaphors, like the tornado in the junkyard, can be helpful for illustrating alternatives to evolution that do not work. And some of them, like typing monkeys, have features relevant to evolution. Overall, though, they don’t help us get a handle on what evolutionary science actually says. Fortunately, there are also metaphors that can help us understand the science. Come back tomorrow for a look at these better metaphors.