Humanoid life on other planets.

[jakesully]

Hi.

I'm here to ask you to settle a debate. Consider movies like "Star Wars", "Star Trek", "Avatar", in which humanoids, barely distinguishable from us, exist on other planets. Is this realistically plausible?

Some friends and myself have been debating this. One side of the debate feels very confident that there is absolutely no way in hell anything even remotely resembling humans exists elsewhere. The other side of the debate says it's not just possible, but highly probable.

What do you think? Talk amongst yourselves.

Irayo, ma'tsukan.

[Darby]

There are reasons to think that convergence might produce humanoid intelligent forms -

http://faculty.fmcc.edu/mcdarby/Pages/h ... aliens.htm

Disclaimer - I wrote this page a few years ago. I wouldn't say the chances are great, but there are ways to rationalize humanoids.

[skeptic]

If we are talking about aliens living elsewhere in the universe, we need to remember that they will have no genetic link to ourselves. All life on Earth appears to have descended from a common ancestor. For example : you share about 50% of your genes with a banana!

However, our hypothetical alien will share zero genes with ourselves. How it will have evolved will be in response to its own unique environment, and that is likely to be very different to Earth.

With no genetic link, or environmental similarity to ourselves, about all we can deduce is that they will be extremely different! Much of this difference will be at subcellular level, of course, with a totally different biochemistry. However, the likelihood of such an alien being humanoid strikes me as very low.

For example : would it have four limbs? There is absolutely no reason why it should. Humans and other terrestrial vertebrates have four limbs for reasons of evolutionary accident. We are descended from lobe fin fishes, which had four limbs. Other fishes have a different number of fins. Had we descended from them, we might have six limbs, or none.

So our hypothetical alien might run around on four legs, and have an extra two limbs for hands, like a weird looking centaur. Or it might have 8, or 800. Or be like an octopus, living in water, and manipulating things with tentacles.

We cannot know anything truly until we meet ET. Anything goes, and probably not much humanoid.