Aliens could be everywhere. There are at least 100bn planets in our galaxy alone, and at least 20% of them could be habitable. Even if a tiny fraction of those planets – less than 1% of 1% – 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. Yet making predictions about aliens is hard because 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 will 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: using 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 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).
In our paper, we use evolutionary theory to make a number of predictions about aliens. We argue that aliens will undergo natural selection. This is something often taken for granted or assumed to be an unknown. We show that there are firm theoretical grounds for believing that aliens will undergo (or have undergone) natural selection.
This article originally appeared in The Conversation
‘Aliens might not have two legs, or any legs, but their structure, from an evolutionary standpoint, will be much more familiar than we might think.’ Photograph: Alamy Stock Photo