In his new book, The Runes of Evolution, Professor Simon Conway Morris makes the argument that evolution follows predictable paths, which includes the eventual development of intelligence, and as such, there should be other intelligent life forms in the galaxy. Conway Morris is a leading evolutionary biologist, but he supports the idea of convergent evolution, a widely though not unanimously supported hypothesis that different species will develop similar features independently.
As a way of example, Conway Morris points out that humans and octopi have evolved similar eyes, although our most recent shared ancestor, a slug-life creature that lived 550 million years ago, lacked the features that our two species now share. Those features had to evolve independently after our branches of the evolutionary tree split apart.
Building on convergent evolution, Conway Morris hypothesizes that Earth-like planets elsewhere in the galaxy, and by extension in the universe, should have seen evolutionary trends similar to Earth’s. Eventually, intelligent creatures would arise that were at least vaguely shaped like us, one head, two arms, and two legs, with tool use and social organization.
The question, though, is why don’t we have any proof of such creatures yet? To date, we haven’t found life anywhere else in the galaxy, despite finding an increasing number of Earth-like planets in other solar systems, far more than we would have estimated even a few years ago. Previous estimates at the number of planets that could sustain life set an extremely low chance of life developing elsewhere, but new research has found planets that, hypothetically, could sustain life in most star systems. Biologists regularly discover creatures capable of living in much harsher conditions than humans and most other vertebrates can manage, so it seems likely that life could develop on all kinds of worlds.
Despite Conway Morris’s argument that life on other planets would evolve along similar lines to Earth, the fact remains that we still don’t know exactly how life began. If we could figure that out, than using convergent evolution, we might be able to figure out where to look, specifically, to find our interstellar neighbors.