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These two desert plants are only distantly related but have independently converged on a very similar—and unusual—body form.

Here on Earth, most evolutionary paths lead in different directions to fill different niches. Species are split from their common ancestor populations to specialize in eating specific foods or surviving in special conditions by utilizing novel mechanisms or behaviors. Every once in a while, two different species will come up with similar solutions to the same problems. This is called convergent evolution. It’s not two species evolving in different places but rather two different species taking advantage of the same principle.

Perhaps the best examples are found in locomotive techniques, which are driven by broad physical laws. All hopping mammals use the same basic methods, even when they aren’t related by another common hopping ancestor. That is to say that there wasn’t just one hopping mammal that gave rise to all the others. Rather, unrelated species came up with the adaptation “by themselves.” Echolocation is another good example. Bats and dolphins developed echolocation AFTER they diverged from their most recent common ancestor but they share the same mutation that allows them to process echos better than we can. They have the same mutation because that’s (presumably) the only mutation that will lead to the proper morphology. Convergent evolution is not an organizing force that changes the laws of probability, it’s just emergent patterns caused by general physical rules.

Neat, right? It gets better. Some mechanisms have arisen identically in almost every single complex species on the planet. Olfactory mechanisms, for instance. We smell things, on a molecular level, the same way as other species who are so distantly related to ourselves that our common ancestor could not smell at all. Mammals and insects both came up with the same olfactory mechanism completely independently.

Of course, we have an extremely small sample size here on Earth but it does suggest an interesting principle. Given the particular physical and chemical laws of our universe, certain adaptations may be hit upon over and over, even on other planets.

This means that if we ever meet an alien race, they may not look like us, they may not think like us and they may not even use our amino acids but they may very well smell like we do. They are likely to have eyes that look like ours.

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