As the old adage goes, when looking up at the stars – what if there’s someone else out there looking back at us. But what exactly would they be looking with?
Eyes are probably one of evolution’s greatest inventions. And that’s saying something, because it’s invented quite a number of things! While convergent evolution means that shapes and ways in which eyes work have evolved to reach much the same conclusion through different pathways, it’s commonly believed that every type of eye on Earth today has a common ancestor. In fact, the first eyes around 540 million years ago weren’t really eyes at all. They would have been little more than light sensitive patches of cells (photoreceptors). Over the following hundreds of millions of years, evolution worked its magic. The result is the overwhelming diversity of eyes which we see around us today.
But the most amazing thing isn’t that eyes exist. It’s that no matter which evolutionary path they take, eyes always end up working in much the same way. The most striking example of this is if you compare a human with an octopus. Both species diverged over half a billion years ago – The most recent common ancestor of the two would have been a primitive worm-like creature. And yet humans and octopodes both have spherical eyes which focus light onto retinas in very much the same way – the pupils may be a different shape, but the end result is just the same. Evolution has independently equipped us with the very same means of visually perceiving the world. We even see the same frequencies of light.
The simple fact of the matter is that the way our eyes work is the most logical way. And the light which we see happens to be the most abundant and easiest to resolve on the planet. The Sun’s light is the brightest in the range which we see, and the atmosphere is the most transparent to it. Nature is the original scientist. It takes everything that’s available to it and reaches the most logical conclusion, without any unnecessary complications. So let’s speculate…
It’s logical to assume that life elsewhere will, where it can, use much the same equipment – provided it made that critical first innovation of photoreception. So if there’s life on a planet like Earth out there, it’s likely that any such life may have evolved eyes of its own. As long as light is abundant and there’s a need to use it to perceive surroundings, eyes are likely to exist so that our hypothetical alien creature may do so. Perhaps around another star, that creature may perceive different wavelengths. Perhaps around a hotter star which emits more ultraviolet, life might see more of the shorter wavelengths available to it. Or around a red star, dim in visible light but bright in infrared, life may see mostly in colours which we cannot – perceiving the infrared rather than our familiar visible spectrum.
Alternatively, if complex life could have evolved to inhabit the oceans under Europa’s crust or subterranean caverns on any other world, it’s likely it would have again taken Earth’s cue – and be completely blind. In the darkness, eyes are an unnecessary waste of energy and life on our own planet has frequently discarded them. Alternatively, they could be like the simpler types of eye found in creatures that live on deep ocean hydrothermal vents, able to sense infrared (and therefore heat) but not necessarily form an image from it.
So in answer to that original question – what could alien life be looking back at us with? Well, if they exist on a world like ours, alien creatures may be looking up at their own starry skies with eyes not unlike ours.
I’m afraid the images are unsourced – they came from an old stock photo CD which I’ve long since misplaced. If anyone can provide me with sources, please do. If you’re curious as to what creatures the eyes belong to, go ahead and click them…