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#1 2018-04-12 17:31:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,058

Convergent evolution? How much convergence?

Let's assume there was life on Mars...

Let's assume there were land based life forms...

Let's assume that Mars evolved independently on Mars from Earth but that Mars was similar to Earth when life evolved.

How much convergent evolution would we see?

My own view is that there would be a lot.

A land creature needs good vision. So good stereoscopic vision seems v. likely to evolve. The actual structure of the eye may be less important than its function.

You might think it makes no difference whether your mouth is above or below your eyes. But if your mouth is above your eyes, then bacterial laden slobber will - thanks to gravity - make its way into your eyes, potentially causing you infection and rendering you defenceless. So surely natural selection will always, but always favour eyes above mouth in land animals. Interestingly, although we've lost quite a lot of facial hair, we haven't lost our eyebrows - showing again the importance of protecting the eyes.

Would bipedal motion always evolve? Hmmm...not so sure about that. Gorillas, chimps and orangutans are all highly intelligent but prefer to move quadrapedal style when on flat ground. But that wouldn't necessarily in my view rule out further evolution.  Shakespeare could have moved on all fours when he went to the local tavern before he sat down to compose a new play.

But something like digits are definitely going to be required at higher evolutionary stages for land based animals I think.  Snake, slugs and snails aren't going to make it to the higher levels because their ability to manipulate the environment and create tools will be strictly limited.  Multiple tentacles seem pretty efficient in the ocean but are probably not so great on land as would require a huge amount of energy to keep aloft when not supported by water.  I presume that's why we don't see tentacled land creatures...so that also implies that a minimal number of limbs - with only two being used "off the ground" is probably something dictated by the energy budget available to land animals.


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