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I realize I'm not a geneticist, but it seems to me that an actual space alien with 3 fingers and 3 toes would have significantly different DNA than humans and other proto-human species.
The portion of DNA that impacts appearance is very very small.

That isn't "appearance" like your eye color or hair color. That would be more along the lines of body plan/embryonic development genes.

I don't know the specifics, but you can be assured that pretty much every higher animal form, from amphibians to mammal, have very similar genes when it comes to encoding body plan. Meaning the same gene/type of gene controls the number of digits in a frog as in a human.

So, it would be a matter of when the gene "turns on" to grow however many digits during embryonic development.

So...I guess you're both wrong? Hell, I'm probably pretty wrong myself. Been a long time since I've pondered such things. Ha.

Edit to add:

It also means that such a thing wouldn't be an unheard of mutation in nature. There are plenty of people born with extra toes and fingers (polydactyls). Why not fewer digits?

This post was edited on 9/18/17 at 9:12 am

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Posted by TigerinATL

Member since Feb 2005

61670 posts

Posted on 9/18/17 at 9:14 am to Sasquatch Smash

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That isn't "appearance" like your eye color or hair color.

Exactly. We are able to tell the lineage of creatures by reading their history in the DNA. You don't go from 5 fingers with an opposable thumb to 3 fingers with some backwoods inbreeding making a few recessive genes dominant. Here's an explanation of how different 3 toed and 2 toed sloths are. They aren't even in the same genetic family (for humans that would be hominid, all of the great apes more or less)

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Although modern two- and three-toed sloths share many characteristics such as their tendency to hang upside down and move slower than molasses, they are not close relatives. Two-toed and three-toed sloths don’t belong to the same family. Two-toed sloths belong to the family Megalonychidae, while three-toed sloths are members of the family Bradypodidae.

So, how did two species that evolved separately become so alike? They are the product of convergent evolution. Convergent evolution is when two different species or genuses develop similar traits because of similar selective pressures in their environments.

Both two- and three- toed sloths belong to the order Pilosa. This family is made up of sloths and anteaters. However, as the phylogenetic tree to the left shows, they evolved separately. Two-toed sloths are closely related to ancient and extinct ground sloths in the families Megatheriidae and Nothrotheriidae, while the three-toed sloth is not.

LINK

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