Aliens are highly likely to undergo natural selection, shows new research.
Aliens could be everywhere. There are at least 100 billion planets in our galaxy alone, and at least 20% of them could be habitable. Even if a tiny fraction of those planets – less than one percent of one percent – evolved life, there would still be tens of thousands of planets with aliens in our vicinity. But if we want to figure out where to start looking for these neighbours, we need to understand what they might be like and where they might thrive. Ultimately, we want to understand as much as possible about an extraterrestrial species before we encounter it. And yet, making predictions about aliens is hard. The reason is simple: we have only one example – life on Earth – to extrapolate from. Just because eyes and limbs have evolved many times on Earth doesn’t mean they’ll appear even once elsewhere. Just because we are made of carbon and coded by DNA doesn’t mean aliens will be – they could be silicon based and coded by “XNA”. However, as my colleagues and I argue in our new study, published in the International Journal of Astrobiology, there is another approach to making predictions about aliens that gets around this problem. That is to use evolutionary theory as a guiding principle. The theory of natural selection allows us to make predictions that don’t depend on the details of Earth, and so will hold even for eyeless, nitrogen-breathing aliens. Darwin formulated his theory of natural selection long before we knew what DNA was, how mutations appeared, or even how traits were passed on. It is remarkably simple, and requires just a few ingredients to work: variation (some giraffes have longer necks than others), heritability of that variation (long-necked giraffes have long-necked babies) and differential success linked to the variation (long-necked giraffes eat more leaves and have more babies).