Gene Involved in Brain Development Evolved Rapidly in Humans

[mark kennedy]

As I keep trying to say, merely stating that it is a "highly conserved region" without understanding why it is a highly conserved region is pointless. Transcription errors, for instance, will be almost independent of location on the DNA strand. Many transcription error mutations would have happened in any gene over a span of 301 million years. The only possible thing that one might use to explain the conservation of that gene is that natural selection prevented it from changing.

Highly conserved in an understatement, for 310 million years it was virtually unchanged. One of the main reasons it was so highly conserved is because it was invovled in the development of the neocortex. An alteration in the sequence could, and probably did, prove fatal to the developing fetus. Natural selection is not based on any known biological or genetic mechanism, it has no bearing on any of this. Once the change is in place and in provides an advantage then it can move toward fixation. That means that the substitutions have to be made in a series that translates into a meaningfull amino acid sequence and then fold into a uselfull protein.

But this doesn't matter, because natural selection ensures it is only those that are beneficial are extended throughout a population. But since it is natural selection that decides whether or not a mutation is beneficial, for how long a mutation is beneficial depends entirely upon the environment. For example, you're probably thinking about the mutations that result in antibiotic resistance in bacteria, mutations that cease to be beneficial once the antibiotic is removed.

Natural selection is not a selection process, it is a massive die off of the less fit. Natural selection does not selected a beneficial mutation, it eliminates deficient populations but never provides anything. More importantly, antibiotic resistance and the human brain are two very seperate issues. You are not comparing apples to apples and it's classic Darwinism that equates the two, not modern genetics.

But take another example: the mutation responsible for sickle cell anemia. This mutation makes those affected resistant to malaria. Thus the mutation is beneficial in any area where malaria is a problem, but detrimental in any area where malaria is not a problem. Thus the gene in question has spread rapidly in those areas where malaria is a problem.

Sickle cell does not create a greater resistance to malaria, what it does is slow the spread of the disease. The blood cell is maleformed so it moves slower and thus slows the spread of the bacteria. Show me any living thing that has blood cells other then round fixed in the population. We are talking about the evolution of the human brain not a deformed blood cell that seems to give a slight advantage.

I see the progression of the HAR1 gene much in the same way: our ancestors, at one point, experienced some environmental, social, or genetic factors that caused a strong amount of selection in this gene. The ancestors of the chicken experienced different circumstances, circumstances that strongly selected against the basically inevitable negative side effects of single mutations in the HAR1 gene.

Selective pressure does not rewrite the genetic code, that is just plain silly. The HAR1 gene was conserved because mutations killed those who had it in the vast majority of the cases. Then all of the sudden some unknown mechanism or mutagen rewrites 18 nucleotides for no apparent reason. You are assuming something without the slightest bit of proof. You offer some anecdotal evidence about a disease and bacterial resistance. Then you take a giant leap into brain evolution without the slightest concern for the deleterious effects of mutations.

But we have proof that humans are descended from chimps through these retrovirus insertion markers!

We have proof that germline invasions are simular in the two lineages but they are hardly any kind of proof of common lineage:

"Endogenous retroviruses. Endogenous retroviruses (ERVs) have become all but extinct in the human lineage, with only a single retrovirus (human endogenous retrovirus K (HERV-K)) still active24. HERV-K was found to be active in both lineages, with at least 73 human-specific insertions (7 full length and 66 solo long terminal repeats (LTRs)) and at least 45 chimpanzee-specific insertions (1 full length and 44 solo LTRs). A few other ERV classes persisted in the human genome beyond the human–chimpanzee split, leaving 9 human-specific insertions (all solo LTRs, including five HERV9 elements) before dying out."

http://www.nature.com/nature/journal/v437/n7055/full/nature04072.html

We therefore need to understand how we descended from apes, not question whether it happened at all.

Horsefeathers! You are saying we should assume unconditionally that we descended from apes which is absurd. You have not offered a dimes worth of real world evidence but you want me to accept a common ancestor without qualification. No thank you, I'll do my own thinking if you don't mind.

The only possible conclusion one can draw if one accepts your arguments is that human evolution was directed. But I'm not willing to give up that easily. We could understand so much more about how the world works by asking how it might have occurred naturally than just giving up and saying, "God did it." (Not that I'm working in this field, but the same issues arise in Cosmology).

No, there are only two possible explanations and they are mutually exclusive:

"Creation and evolution, between them, exhaust the possible explanations for the origin of living things. Organisms either appeared on earth fully developed or they did not. If they did not, they must have developed from preexisting species from some process of modifications. If they did appear in a fully developed state, they must have been created by some omnipotent intelligence." (D. J. FUTUYMA Science on Trial (1983))

It's wrong to say God did it but it's ok to say God didn't do it and you would have me believe that that is science.

Baloney!

Have a nice day
Mark

 

[Chalnoth]

I'm getting rather tired of this argument, I'm sorry to say. I'm going to leave with this last closing statement:
Natural selection is dependent upon everything in the environment, from the organism itself, to the other organisms in the ecosystem, to the other genes in the genome, to the weather, to the social structure of the organism, and so on and so forth. If you can't understand why the chicken's ancestral line might have conserved the HAR1 while ours didn't due to different selection pressures, then we just don't have anything more to talk about.

The quick evolution of the HAR1 gene in humans is interesting, but it isn't damaging at all to evolution.

 

[Chalnoth]

Well, I guess I couldn't leave well enough alone. I would like to summarize the points that I have attempted to make, in a more logically-connected manner.

1. Humans, chimpanzees, and gorillas share a common ancestry. We have some incredibly compelling evidence as to this common ancestry in retrovirus insertion:
http://www.talkorigins.org/faqs/comdesc/section4.html#retroviruses

The insertion events that characterize this method are so rare, and even more rarely passed on to offspring, that finding the same insertion signature between two separate organisms is a sure sign of common ancestry.

There are, of course, other pieces of evidence, but I personally think this is the most compelling.

2. If we evolved from apes, the only question remaining is how did we evolve from apes? In investigating this evolution, we find many interesting things, such as the large number of mutations in the HAR1 gene. Abnormal events like this have the potential for unearthing rich information about evolution.

3. Stating that evolution cannot have caused the evolution of this gene is tantamount to giving up. That is to say, consider that we have two ways of tackling this problem. The first is to say that a natural process led to this evolution. The second is to say that God did it. The first option requires that we generate a plausible explanation, and one that could potentially be applied to other evolutionary lines. There are sure to be a number of plausible explanations, and these must each be examined, in particular to see if predictions can be made based upon them, so that we can test those predictions and eliminate them one by one. Choosing to use God as an explanation leads to no predictions at all, leads to no possibility of further understanding our world, and is, therefore, giving up.

Anyway, now that I think I've made my point more clear, I'll be more satisfied to walk away.

 

[mark kennedy]

I'm getting rather tired of this argument, I'm sorry to say. I'm going to leave with this last closing statement:
Natural selection is dependent upon everything in the environment, from the organism itself, to the other organisms in the ecosystem, to the other genes in the genome, to the weather, to the social structure of the organism, and so on and so forth. If you can't understand why the chicken's ancestral line might have conserved the HAR1 while ours didn't due to different selection pressures, then we just don't have anything more to talk about.

I understand perfectly, when you don't have an explanation you just enter the magic word, natural selection. That is supposed to explain everything and it explains nothing at all. I do understand that a gene preserved for 310 years to suddenly accumulate 18 substitutions is unprecedented acceleration.

The quick evolution of the HAR1 gene in humans is interesting, but it isn't damaging at all to evolution.

Again the distinction of evolution as being natural science and natural history is blurred. It is only the most simplistic of reasons that lead one to accept such a broad concept is such absolute terms. It is unfortunate that you were not interested in looking closer at this fascinating research project. They have only looked at the first segment with 48 more to go.