Converging on the Alien
Convergent Evolution and the Potential for Alien Life
What would aliens look like if we met them one day?
That’s one of the questions I love to bring into my talks for younger students (and adults, too). It’s fun to think about the various “aliens” that we’ve seen in movies and video games and such and to wonder if we got anything right.
Certainly in Star Wars, Star Trek, Mass Effect, and more we’ve created aliens that help us tell human stories. It’s not then surprising that we see things that are similar to what we know in these stories: many aliens in sci fi are presented as humanoid with some small changes. But how alike will aliens really be to us? What kinds of similarities might we find? Is it possible that evolution of alien life may have led to the convergence of certain forms that we find here on Earth?
Perhaps by studying convergent evolution within our own biosphere, we can gain insights into the key features of life on Earth that we may also expect to find in alien life forms
Convergent evolution is a phenomenon in which unrelated species independently evolve similar traits or characteristics in response to similar environmental pressures. A key example that many people have heard of is flight: the ability to fly has arisen within birds, insects, and bats and yet their evolutionary pathways to get to flight are not connected. This might be a telling sign that the evolution of wings in animal-like creatures on alien worlds should be likely.
But there are some other convergent traits that we might want to consider for alien biospheres as well.
Bioluminescence, echolocation, and the development of camouflage are all convergent traits. Maybe there are alien biospheres where glowing, flying creatures use their luminescence to light the skies while some ground creatures on the surface below use their camouflage to seamlessly blend in while their echolocation allows them to avoid predation.
Of course, when it comes to convergent processes in evolution, we can also look to simpler fundamental processes of biology.
For instance, we have good reason to assume that some alien life forms (and maybe most) will also use water as a solvent and are carbon-based in their molecular makeup. While we don’t know if the use of DNA and RNA for storing and passing on information is necessary, there’s good reason to assume that an alien life that also has cellular structures and evolves along similar modes as life as we know it would also then require some form of information storage, processing, and transfer. And many of the metabolic processes for life as we know it are likely to be found to be convergent across other alien life forms that may be out there — life as we know it relies on processes of moving electrons from one molecule to another for energy storage and use. It makes sense to assume that many of those processes on Earth, which are very much guided by the physics and chemistry of the environment, would also be found elsewhere.
But these fundamental convergences probably aren’t as fun for some people to think about. Let’s explore three intriguing convergences for larger, multicellular beings on Earth and what that might mean for life “out there”.
In one of my posts shared on my social media platforms that highlighted three convergent forms for life as we know it (and that we might expect elsewhere):
Caption: The artwork in this image was created by Alex Ries while the addition of the words were added by someone before it was posted on the Wild Green Memes for Ecological Fiends Facebook Group.
These three fascinating examples of convergent evolution include the evolution of trees, the development of snakes from lizards, and a process termed carcinization.
The convergent evolution of trees is a remarkable phenomenon.
Different lineages of plants, including gymnosperms like conifers and angiosperms like flowering plants, have independently evolved tree-like structures — believe it or not, there is no single scientific classification of a tree. These towering giants, with their tall trunks and branching canopies, have adapted to exploit vertical space and capture/compete for sunlight more effectively. Despite the disparate evolutionary origins, the convergent evolution of trees demonstrates nature's recurrent solution to optimize growth and survival in diverse environments. In the film Avatar, we saw one possible take on an alien tree in the form of the gigantic structure known as “Hometree”.
Another intriguing instance of convergent evolution is the development of snakes and other legless lizards from lizards with legs — and honestly might even apply to marine mammals and other forms that have evolved from the loss of certain features or appendages. Snakes are specialized reptiles that have lost their limbs and acquired elongated bodies, enabling them to slither and capture prey with astonishing precision. Surprisingly, snakes have independently evolved from different lineages of lizards multiple times throughout known evolutionary history.
This convergence in body shape and locomotion highlights the evolutionary advantages of a limbless body form in specific ecological niches, such as burrowing or aquatic habitats.
Carcinization is yet another fascinating example of convergent evolution that refers to the repeated independent evolution of crab-like forms in different crustacean lineages.
Despite belonging to diverse groups (such as crabs, hermit crabs, and squat lobsters), these crustaceans exhibit similar body shapes, with a broad carapace and jointed appendages for walking sideways and pinching. This convergence in body structure suggests that the crab-like form provides significant advantages for survival and adaptation to specific marine habitats and may even be a form we will likely find elsewhere.
In the picture above that I shared to social media, I actually garnered a lot of responses from people suggesting various convergences they would expect.
Here are some of my favorites answers:
Hearing - Deep Sky Dude
Oxygenic Photosynthesis - Lee Billings
Chemolithotrophy - Anurup Mohanty
Biofilms - Augusto Carballido
Fungal-like structures - Danielle Froom
Purple plants - Matt Williams
Heat regulation - Kristoff Biernat
There are many possible ways to envision alien life converging on similar molecules, processes, body forms, and attributes to life as we know it.
Thanks to the various modes of evolution, life on Earth has become remarkably flexible in adapting to new environments and finding similar solutions to the same types of problems. But perhaps life on an alien world would truly evolve quite differently. Perhaps we may not even recognize an alien life form if we met it. But studying convergent evolution on Earth may provide us with insight on how an alien biosphere may solve similar problems that life here has faced.
From flight and camouflage to the development of trees and crablike body plans, there are many things we see within the remarkable diversity of life here on Earth that we might expect to have occurred elsewhere.
A couple of big questions for many of us then wondering about what alien life might be life, is what things could have happened here but didn’t and what forms of life could exist out there that truly are completely alien to what we know?
The only true way for us to ever answer such questions will be to find alien biospheres out there among the stars.
Perhaps one day we will be able to study them. Or, if they have evolved intelligence and sentience of some form, perhaps we will even be able to have a conversation about our similarities and differences. That would truly take what many of us have dreamed of in science fiction and open it up to an entirely new reality.