In a recent discussion with creationists, a claim was made that humans might not be of the primate evolutionary linneage.

This was based on the human abilty to carry/synthesise beta keratin, unlike all other primates, but not unlike birds and reptiles. With the further claim that a genetic mutation since the time we branched from the last common ancestor (with chimps) leading to a species wide adaptation is unlikely, because the selection pressures required for it to propogate to this extent are unlikely (or at least, that's the claim). So therefore, this trait is likely to have been inherited from the avian or reptile evolutionary line.

This would seem a bit like finding fossils in the wrong layer if it were true, and it sounds more like the creationist habit of arguing anything that could conceivably undermine evolutionary theory. But as a non biologist thought it would be better to ask someone with further understanding of the subject.

What are your thoughts on this re homonid/ human evolution? Do you know of any reasonable (to a non biologist) literature that deals with it?

I really wouldn't waste your time arguing in this way - most creationists have no interest in reasoned debate, rather they want to persuade you (and through you others) that you are wrong. Failing that they generate a miasma of uncertainty and doubt to try and undermine science. In this case just pause for second and ponder on the daftness of saying humans are not primates!

Alpha-keratin is produced by humans, primates and other mammals, beta-keratin is present in birds and reptiles.

A recent abstract at a meeting (see below) has shown that a small amount of human keratin can take up the beta form as well as the vast majority which is the alpha form. That is less likely to be genetically determined and says more about the 3 dimensional arrangement of the keratin chains. Why someone thinks that means human are not primates or directly descended from birds is beyond me!
https://www.sciencedaily.com/releases/2 … 142412.htm

I agree with David - in the literature where ‘beta forms’ of keratin have been described in humans (e.g., see - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1304386/) people are usually referring to ‘beta sheets’ or ‘beta turns’ (the secondary structure form) rather than beta-keratin proteins themselves which have different amino acid compositions to the alpha-keratins. There are lots of distinct, structurally-related forms (over 50 functional in humans; nomenclature KRT) of keratins whose amino acids are arranged in an alpha-helical conformation, but DNA/genome databases (e.g., NCBI; http://www.ncbi.nlm.nih.gov/) show no entry for a human ‘beta keratin gene’.

By the way, as you probably know keratins are a major component of intermediate filaments, one of the 3 major types of cytoskeleton fibres in cells (the other two are the actin microfilaments and the microtubules) - there are some stunning pictures of these on-line (google image search keratin intermediate filaments).

Last edited by Steve Lolait (29th Mar 2016 11:43:05)