2
$\begingroup$

I am referencing this video, where a caterpillar turns into what looks like a snake when it gets frightened, presumably to ward off predators.

Now how can this evolve?

I majored in Molecular Neurobiology and studied evolution, and random molecular evolution makes sense to some degree. Every now and then there are random mutations, sometimes which affect gene / cell-signaling pathways, which could cause reproductive advantages, leading to evolutionary adaptations. But to go so far as to be able to mimic an external structure like a snake, how is that possible? I don't see how that can randomly evolve.

It is as if as a species we have a plan on what we want to become, and we slowly realize that plan by somehow tuning the genes to, say, look like a snake. But that is just me trying to fill in the gaps with imaginative thinking, how something like this can evolve. There are many other examples of incredible things evolving, but this one demonstrates the question perfectly.

Briefly, can you explain how this sort of thing could evolve?

$\endgroup$

2 Answers 2

7
$\begingroup$

Mutations are random; natural selection is not.

Caterpillars are eaten by animals like birds. If you get eaten as a caterpillar you don't get to reproduce, so there's a strong selection for anything that makes you less likely to get eaten.

Even a very basic snake-like appearance (maybe just a color) might cause some survival benefit - maybe not every caterpillar with that gene survives, but over generations more snake-like caterpillars survive than non-snake-like, so the population looks more snake-like.

I don't see the snake-like behavior part as any different evolutionarily from the appearance part, or distinct from any other defensive behaviors that animals make, such as posturing to look larger, etc. It's just a behavior that's unlikely to be beneficial until after the other appearance changes. No planning is necessary at any stage, just selection on characteristics that appear.

Be wary, too, of selection bias when thinking about the evolutionary likelihood of any one thing: you observe the things that did evolve, not all the things that are possible.

$\endgroup$
2
$\begingroup$

Because vision is not perfect, a predator could confuse a caterpillar for a snake under different conditions at different distances. is it cloudy out, is the caterpillar in shadow, partially obscured. At every step of looking more like a snake the caterpillar is less likely to be eaten in more and more situations. this is fairly easy to see because there are a variety of caterpillars that resemble snakes to varying degrees. Many are just simple spots that look like eyes. Even if it only fools only a few predators under only a few conditions it is still an advantage. This is why mimicry in general is so common.

enter image description here

enter image description here

Consider the certainty of a predator, if the predatory is just confused about whether something is or is not a snake, it can still be a big advantage. That might be a snake but that other thing is definitely a caterpillar. Which one is the predator going to investigate the possible threat or the easy meal? Then the caterpillar that does not resemble a snake gets eaten and the poor mimic gets spared. Prey selection is a risk assessment and a certainty assessment at the same time, thus is exploitable.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .