Human Brain Still Changing?

[damocles]

http://www.hhmi.org/research/investigators/lahn.html

 

The gist of the research is that two genetic markers; that Doctor Bruce T. Lahn has time dated indicated that some genetic changes occured in humans' brains about the same time that cities and written language show up in the human archaeological footprint.

 

The two candidates are;

 

Employing the above strategy, we identified a number of candidate genes that might have played a role in the evolution of the human brain (candidate “humanness” genes). In humans, homozygous loss-of-function mutations in two of these genes, ASPM or Microcephalin, cause microcephaly, a congenital developmental defect characterized by severely reduced brain size. Although their brains are smaller, affected subjects have relatively normal brain structure and no overt abnormalities outside of the nervous system. Based on these observations, it was concluded that ASPM and Microcephalin are specific regulators of brain size. The two genes share a similar set of evolutionary properties. First, they show significantly accelerated evolution in primates relative to nonprimate mammals. Second, within primates, this acceleration is most prominent in the lineage leading to humans. Third, comparison of interspecies divergence data with human polymorphism data confirmed that the accelerated evolution in the human lineage is likely due to positive selection. Finally, the accelerated evolution appears to be highly localized within specific regions of these genes, suggesting that positive selection has targeted certain domains of the genes more intensely than others. The above data provide compelling evidence that ASPM and Microcephalin have been the target of strong positive selection during primate evolution, and such selection is most prominent in the human lineage.

 

I expect that this hypothesis will be the subject of considerable controversy.

 

http://www.hhmi.org/news/lahn4.html

 

September 09, 2005

Human Brain Is Still Evolving

Howard Hughes Medical Institute researchers who have analyzed sequence variations in two genes that regulate brain size in human populations have found evidence that the human brain is still evolving.

 

They speculate that if the human species continues to survive, the human brain may continue to evolve, driven by the pressures of natural selection. Their data suggest that major variants in these genes arose at roughly the same times as the origin of culture in human populations as well as the advent of agriculture and written language.

 

“We want to know how broad a trend these two genes represent. Did we get really lucky and hit on two rare examples of such genes? Or, are they representative of many other such genes throughout the genome?”

Bruce T. Lahn

 

The research team, which was led by Bruce T. Lahn, a Howard Hughes Medical Institute investigator at the University of Chicago, published its findings in two articles in the September 9, 2005, issue of the journal Science.

 

Their analyses focused on detecting sequence changes in two genes - Microcephalin and “abnormal spindle-like microcephaly associated” (ASPM) - across different human populations. In humans, mutations in either of these genes can render the gene nonfunctional and cause microcephaly - a clinical syndrome in which the brain develops to a much smaller size than normal.

 

In earlier studies of non-human primates and humans, Lahn and his colleagues determined that both Microcephalin and ASPM showed significant changes under the pressure of natural selection during the making of the human species. “Our earlier studies showed that Microcephalin showed evidence of accelerated evolution along the entire primate lineage leading to humans, for the entire thirty to thirty-five million years that we sampled,” he said. “However, it seemed to have evolved slightly slower later on. By contrast, ASPM has evolved most rapidly in the last six million years of hominid evolution, after the divergence of humans and chimpanzees.”

 

In order to identify sequence changes that occurred in Microcephalin and ASPM in the evolutionary lineage leading to humans, Lahn and his colleagues took the following approach: They determined the DNA sequences of the two genes among a large number of primate species and searched for sequence differences between humans and nonhuman primates. By doing statistical analysis on these sequence differences, they could demonstrate that the differences were due to natural selection that drove significant sequence changes in the lineage leading to humans. These changes accumulated presumably because they conferred some competitive advantage.

 

The evidence that Microcephalin and ASPM were evolving under strong natural selection in the lineage leading to humans led Lahn and his colleagues to consider exploring whether these two genes are still evolving under selection in modern human populations. “In the earlier studies, we looked at differences that had already been set in the human genome,” he said. “The next logical question was to ask whether the same process is still going on today, given that these genes have been under such strong selective pressure, leading to the accumulation of advantageous changes in the human lineage. If that is the case, we reasoned we might be able to see variants within the human population that are rising in frequency due to positive selection, but haven't gone to completion yet.”

 

The researchers first sequenced the two genes in an ethnically diverse selection of about 90 individuals. The researchers also sequenced the genes in the chimpanzee, to determine the “ancestral” state of polymorphisms in the genes and to assess the extent of human-chimpanzee divergence.

 

In each gene, the researchers found distinctive sets of polymorphisms, which are sequence differences between different individuals. Blocks of linked polymorphisms are called haplotypes, whereby each haplotype is, in essence, a distinct genetic variant of the gene. They found that they could further break the haplotypes down into related variants called haplogroups. Their analysis indicated that for each of the two genes, one haplogroup occurs at a frequency far higher than that expected by chance, indicating that natural selection has driven up the frequency of the haplogroup. They referred to the high-frequency haplogroup as haplogroup D.

 

When the researchers compared the ethnic groups in their sample for haplogroup D of ASPM, they found that it occurs more frequently in European and related populations, including Iberians, Basques, Russians, North Africans, Middle Easterners and South Asians. That haplogroup was found at a lower incidence in East Asians, sub-Saharan Africans and New World Indians. For Microcephalin, the researchers found that haplogroup D is more abundant in populations outside of Africa than in populations from sub-Saharan Africa.

 

To produce more informative statistical data on the frequency of haplotype D among population groups, the researchers applied their methods to a larger population sample of more than one thousand people. That analysis also showed the same distribution of haplogroups.

 

Their statistical analysis indicated that the Microcephalin haplogroup D appeared about 37,000 years ago, and the ASPM haplogroup D appeared about 5,800 years ago - both well after the emergence of modern humans about 200,000 years ago. “In the case of Microcephalin, the origin of the new variant coincides with the emergence of culturally modern humans,” said Lahn. “And the ASPM new variant originated at a time that coincides with the spread of agriculture, settled cities, and the first record of written language. So, a major question is whether the coincidence between the genetic evolution that we see and the cultural evolution of humans was causative, or did they synergize with each other?”

 

Lahn said that the geographic origin and circumstances surrounding the spread of the haplogroups can only be surmised at this point. “One can make guesses, but our study doesn't reveal how these positively selected variants arrived," he said. "They may have arisen in Europe or the Middle East and spread more readily east and west due to human migrations, as opposed to south to Africa because of geographic barriers. Or, they could have arisen in Africa, and increased in frequency once early humans migrated out of Africa.”

 

While the roles of Microcephalin and ASPM in regulating brain size suggest that the selective pressure on the new variants may relate to cognition, Lahn emphasized that this possibility remains speculative. “What we can say is that our findings provide evidence that the human brain, the most important organ that distinguishes our species, is evolutionarily plastic,” he said. Finding evidence of selection in two such genes is mutually reinforcing, he pointed out. “Finding this effect in one gene could be anecdotal, but finding it in two genes would make it a trend. Here we have two microcephaly genes that show evidence of selection in the evolutionary history of the human species and that also show evidence of ongoing selection in humans.”

 

Lahn emphasized that it would not be correct to interpret the findings as indicating that one ethnic group is more “evolved” than another. Any differences among groups would be minor compared to the large differences in such traits as intelligence within those groups, he said. “We're talking about the average impact of such variants,” he said. “We still have to treat each individual as an individual. Just because you have one gene that makes you more likely to be a little taller, doesn't mean you will be tall, given the complex effect of all your other genes and of environment.” Lahn also said that a multitude of other genes likely exist that influence brain size and development, and further research could reveal far more complex effects of natural selection on such genes.

 

Lahn speculated that the new findings suggest that the human brain will continue to evolve under the pressure of natural selection. “Our studies indicate that the trend that is the defining characteristic of human evolution - the growth of brain size and complexity - is likely still going on. If our species survives for another million years or so, I would imagine that the brain by then would show significant structural differences from the human brain of today.”

 

For both Microcephalin and ASPM, Lahn and his colleagues are trying to find out the precise traits that are under natural selection. They are also performing more detailed studies of the two genes in human populations to better understand their evolutionary history. And they are searching for other brain-related genes that have changed under the pressure of natural selection. “We want to know how broad a trend these two genes represent,” said Lahn. “Did we get really lucky and hit on two rare examples of such genes? Or, are they representative of many other such genes throughout the genome. I would bet, though, that we will find evidence of selection in a lot more genes.”

 

Lahn and his colleagues are now working to understand how subtle changes in the sequences of these two genes can alter their function in such a way that would result in favorable selection. While there is some evidence from earlier studies that Microcephalin and ASPM code for proteins that regulate the proliferation of brain cells from immature neural stem cells, their function has not yet been determined, said Lahn.

 

As based on the above articles: the hypothesis, the investigative techniques used to investigate it and the observed conclusions from the research I expect to come under quite severe peer review.

[CraigD]

Controversial or not, Lahn’s hypothesis that significant changes in brain anatomy is an attractive answer to a persistent question: Why, if as archeological evidence suggest, humans have been grossly anatomically modern for 200,000 years, didn’t they do anything behaviorally modern for the first 190,000 years or so?

[Turtle]

___It's pretty hard to come up with archeological behavioral evidence as it is. Even well preserved artifacts attributed to behaviors (statuary, altars, tools, etc.) have inferred behavioral attributes hotly contested. Only recently did a 5,000 year old bison skull with an embedded stone spear point place the atlatl technology in the SW during that time period.

___190,000 years is plenty of time to erase human evidence; look what Katrina did to the Gulf Coast in just days, or Popeii & Herculaneum for that matter.

___This new work is very interesting; punctuated evolution anyone? :hihi:

[lindagarrette]

It makes sense that genetic changes are occurring all the time so why dispute that it is going on with the brain? But evolution implies a survival criteria. What could it be in this case? There has to be something evident to mating pairs that makes the new version more appealing.

 

http://www.hhmi.org/research/investigators/lahn.html

 

The gist of the research is that two genetic markers; that Doctor Bruce T. Lahn has time dated indicated that some genetic changes occured in humans' brains about the same time that cities and written language show up in the human archaeological footprint.

 

The two candidates are;

 

 

 

I expect that this hypothesis will be the subject of considerable controversy.

 

http://www.hhmi.org/news/lahn4.html

 

 

 

As based on the above articles: the hypothesis, the investigative techniques used to investigate it and the observed conclusions from the research I expect to come under quite severe peer review.

[damocles]

___It's pretty hard to come up with archeological behavioral evidence as it is. Even well preserved artifacts attributed to behaviors (statuary, altars, tools, etc.) have inferred behavioral attributes hotly contested. Only recently did a 5,000 year old bison skull with an embedded stone spear point place the atlatl technology in the SW during that time period.

___190,000 years is plenty of time to erase human evidence; look what Katrina did to the Gulf Coast in just days, or Popeii & Herculaneum for that matter.

___This new work is very interesting; punctuated evolution anyone?

 

By Turtle

 

 

I agree. The only inferable evidence that we have for the above hypothesis is the grossest evidence that observers can see: persistent writing, city building, and human use of money that we find in the archaeological record across Mesopotamian, Egyptian, Indian, Chinese, Mediterranean, Northern European and Amerindian cultures. City building, to take one example spread across the species within a particularly brief period. It manifested itself with remarkably similar engineering linearity among the cultures. Piled brick led to the post and beam. then gave way to the arch, and then to the braced strut. This occurred in the remarkably short time of five to ten thousand years. It also appears to have erupted in the Middle East and spread across Europe and Asia in a straightforward process of geographic diffusion via people migration. This is a very clear set of(generally) agreed archaeological observations.

 

The question for the punctuated evolution crowd was/is, what human niche/island ecology first showed persistent human city building(hive behavior?)? Then the archaeo-geneticists have to figure out some kind of valid genetic drift mapping with markers to see if they can match the origin points of geographic diffusion of persistent city building in time with the increased influence of Microcephalin and “abnormal spindle-like microcephaly associated” (ASPM) across the human populations? That investigators have to look for the grossest of one to one coincidences between the two(suggested) markers is evident from the poverty in the archaelogical record below the blatantly obvious that we can successfully interpret with confidence; as well as the need for a CLEAR archaeological test marker that can negate the above hypothesis. We have a reasonably good idea when persistent city building shows up by geographical distribution, so I suggested this for the test marker.

 

The coincidence in time and geography of persistent city building with the increased influence of ASPM in human brains across in a set of multiple data points matched to emergent civilizations' appearances, of course, is insufficient to prove the hypothesis; however, if discrepancies were to show in the expected distributions between the two data sets, then the above hypothesis presented could be negated. It is the most plausible first test.

[Boerseun]

Genetic material changes with every generation.

 

Sadly, however, for the human species evolution has come to a complete and utter dead stop. With a loud, meaty THUD.

 

Why, you ask?

 

Well, let me tell you:

 

We embrace, boost, support and glorify mediocrity.

 

We make it possible for the dredges of society to have the highest birthrates, whilst those contributing the most (research, taxes, arts) settle for a no child/1 child lifestyle.

 

The dredges of society aren't necessarily the dredges because of race/prejudice/previously disadvantage, or any such liberal crap - some people are down in the gutter because genetically, biologically, they can't be anywhere else. And we make it possible for them to have five to ten kids.

 

Who's gonna be in charge of the human gene pool in 50 years?

 

The scientists? The social leeches?

 

Keep in mind - from ancient Greece till today, who advanced humanity? The social leeches, or the scientists?

 

Evolution for humans also took a bad turn when orthodontical braces were introduced. Now, you can breed with a beautiful lady without knowing she can actually eat corn off the cob through a tennis racket, genetically speaking. You're gonna have one hell of a surprise once your first kid gets born, though. Imagine, for a second, that you had braces as well, without your ex-buck-toothed wife knowing about it?

 

The entire field of medical sciences has rendered evolution rendundant for humans - and veterinary sciences threaten to do so very soon for domesticated animals. All we can hope for is that we have indeed reached the apex biologically, seeing as from here on forward, our genetic material is only going one way - DOWNHILL.

[damocles]

The entire field of medical sciences has rendered evolution rendundant for humans - and veterinary sciences threaten to do so very soon for domesticated animals. All we can hope for is that we have indeed reached the apex biologically, seeing as from here on forward, our genetic material is only going one way - DOWNHILL.

 

By Boerseun

 

I believe that view is pessimistic. C.M. Kornbluth wrote about this problem in a story called "The Marching Morons".

 

I have hope, though, in two solid factors that pessimists often overlook.

 

First, historically as well as epochally, the vast majority of species' breeders have ended in dead ends, while some niche breeders or small group within the species has erupted out of the genetic mean with an enhancement that spreads across the ecology like wildfire to establish a new equilibrium within the species until it differentiates itself into a new species. Recessive characterisrtics kill themselves off by being unsuccessful breeders while successful ones supplant the unsuccessful.

 

In other words, pessimists may confuse human survival successes with human survival failures. Teeth may be replaced by dentures or an electric food blender.

 

The second factor is Stephen Hawking.

 

By all rights he should be dead. He certainly is ill enough that he shouldn't be alive without assistence. Yet that assistance has kept him alive long enough to continue to fundamentally redirect our understanding of our existence. Call that one small incremental step in human "cultural evolution".

 

Our persistence in maintaining the weak and less biologically successful breeders among us has paid off in some remarkable species advantages over our animal competitors.

 

It is leading us medically toward genetic manipulation.

 

It may be soon possible to forget about braces and poor eyesight if you can fix it in the fertilized egg.

 

I am an optimist.

[Boerseun]

The second factor is Stephen Hawking.

That's my point, see.

 

Stephen Hawking isn't 'breeding', to put it mildly.

 

Sperm banks the world over should be begging Mr. Hawking for a small, shall we call it, 'donation'.

 

In stead, the majority of breeders of this mostly blue (there might be some poetic justice in that) planet of ours is the poor, the down-trodden, the illiterate, the people who find a large part of their daily entertainment quota in sex.

 

And not only that: Imagine, if you will, a world where the ability to count things adds to your chances of survival. The ability to reason abstractly, to remember things, to bring things into perspective, to draw relationships between seemingly unrelated events/issues/parts/whatever. Such a world, with such abilities, made homo sapiens lord it over neanderthal man. In such a world, the ability to outsmart a sabre-toothed tiger meant survival, and the opportunity to procreate.

 

Today, such abilities are useless. Hand-held calculators have dumbed down the vast majority of our population to the point where most people won't think you're making a joke if you tell them one plus one is actually nine. They can't refute your statement without a CASIO CX-940 in their left hand, the right punching away at tiny little buttons. Will it lessen their chances to breed?

 

Drawing relationships between objects is a computer keyboard away. Will the inability to do even this lessen their chances to breed?

 

We are dumb. Let me rephrase that. We are DUMB. Capital. And getting dumber every single day. Animals evolve rapidly when their population shrinks, and is forced to go through a crisis bottleneck. Ice ages, meteor impacts, global disasters are cases in point. The species need to be small enough in numbers for any specific change to become rapidly distributed. The human race is currently the biggest (numerically speaking) mammalian species on the face of this planet. Probably the biggest ever. The BIGGEST BY FAR. Which means that our gene pool is so big, that any beneficial change will only become rapidly diluted, only to disappear. Negative changes will distribute, and won't harm the species (or the individual) as it should in nature, because our culture has found ways around it. Welfare, the Dole, etc. Problem is, by and large, and statistically speaking as well, there's a heck of a lot more negative changes for every single positive change. You do the math. We are DOOMED. Thanks to altruism and technology.

 

Embrace pessimism. At least you'll never be disappointed.

[damocles]

If you want biological bottlenecks;

 

1. Oil shortage.

2. Potable water shortage.

3. Climate change.

4. Bio-diversity killoff(In progress as I write this due to human encroachment on habitat and alien cross species invasion of ecologies thanks to parasitical riders on aircraft and ships)

 

should be more than enough to guarantee a massive killoff of humans within the next few hundred years barring sensible species wide adaptation.

 

Once again the survivors will be the ones who are smart enough to anticipate and adapt their human behaviors to the changed conditions.

 

Those will be the ones who solve the heat pollution and the energy shortage problems.

 

True they might only contribute a small donation to the genetic pool.

 

But then again throughout the history of humanity it hasn't been that many of us who changed the fundamental way we do things.

 

Nor has it been proved that their specific children have substantially equaled their parents in intellectual achievement in human history.

 

On the other hand, the schmucks(me) seem to catch on quickly enough when one of these geniuses causes a paradigm shift in tool using and we adapt quickly. That is a sensible read on why schmucks continue to predominate?

 

You may be correct in pointing out that using calculators and computers make many of us(schmucks) lazy thinkers.*

 

On the other hand, I do not see it affecting you in the use of logic and example when you present your case.

 

*I blame public education more than I blame technology for inability to think. If you hire incompetent teachers, don't be surprised by the incompetently taught.

[Turtle]

... The human race is currently the biggest (numerically speaking) mammalian species on the face of this planet. Embrace pessimism. At least you'll never be disappointed.

___I think bats have the honor of the numerically largest population of mammals. :hihi:

___I embrace optimism; pessimism embraces me. Bring on the next ice age or meteor strike; I'm ready to evolve. :lol:

[CraigD]

When I read the article about Lahn’s research, the first thing to enter my mind was the recollection of this quote

For millions of years, mankind lived much like the animals. Then something happened which unleashed the power of our imagination: The urge to talk.

-Stephen Hawking

Although I enjoy his writing, I don’t ordinarily remember Hawking quotes, but this is one of the few to enjoy heavy radio play, in the intro to Pink Floyd’s 1994 song “Keep Talking”.

 

Hawking was playing fast and lose with the numbers in this quote – anatomically modern mankind – H. Sapiens – appears to have existed only hundreds of thousands, not millions of years – but he captures the mystery of which I spoke quite poetically: If humankind has been anatomically the same for so long, why did they (we?) spend so long behaving so differently than we do now? If human beings 100,000 (or as much as 400,000) years ago had the same brains and bodies that we do now, surely they’d have come up with most of the big human ideas - language, agriculture, science and technology, etc. – within at most a few thousand years.

 

Lahn’s hypothesis is compelling because it offers an explanation that William of Ockham or Sherlock Holms would appreciate for its simplicity: they didn’t have such ideas because they didn’t have the same brains we do now.

 

Proving this explanation right may be difficult, or Lahn’s conclusions may even prove wrong, but until then, the explanation is at least satisfying.

[Fishteacher73]

It seems that people either want to take the prospect of gradualism and PE as mutually exclusive concepts. Granted the idea of gradualism "marching onward to a 'improved' species" model seems to be a bot outdated and a bit IDish, the ideas of genetic drift and constant subtle change seems well established. The fossil record also seems to support the concept of PE.

 

These two forces can be working indeopendent of each other and still be in action. PE seems to take into account external changes a bit more and gradualism seems to be finetuning of existing traits.

 

If I recall correctly the rise of agriculture coincided with the recession of the last ice age. This produce more arid seasons, and more annual type growth with seeds that more storage and thus more nutrition. I think that this is the advantage of agriculture, not a nerological leap, but a botanical shift.

 

As for language, many feel that the origins are onomatopoeic words which exist in every language. Essentially mimicry of our surroundings. And today many children learn these types of words much quicker than the symbolic words that we use in language.

[Turtle]

Excellent discourse; I love science. I must wonder if humans brains enlarged & then they built cities & tended crops, or if humans grew crops, built ciites & this "caused" their brains to enlarge? Does one do a lot of simple things in the belief this produces synergy, or does one lay off & wait for the synergy & then employ it? I love science! :hihi:

[CraigD]

Larynxes, language, and the emergence of humankind

 

It seems that people either want to take the prospect of gradualism and PE as mutually exclusive concepts.

Where this thread is concerned, I’m trying to avoid “big picture” evolutionary terms like gradualism and punctuated equilibrium, and focus just on one event – “the emergence of modern humankind.” I’m especially trying to avoid speculation about any continuing process that might lead to “the emergence of the next modern humankind.”

If I recall correctly the rise of agriculture coincided with the recession of the last ice age. … I think that this is the advantage of agriculture, not a nerological leap, but a botanical shift.

I’d be more moved to agree if the ice ages had effected all H.Sapiens-populated places on earth, but they did not. Since the speciation into H.Sapiens 300-400KY ago, it appears there’s never been less than a sizable population of them/us in a place hospitable to the development of modern agriculture, and all the rest of modern human culture. The only conclusion I’m able to draw is that the innovation didn’t occur because H.Sapiens was somehow incapable of it.

As for language, many feel that the origins are onomatopoeic words which exist in every language. Essentially mimicry of our surroundings. And today many children learn these types of words much quicker than the symbolic words that we use in language.

I read an interesting article in the past year or 2, in which an evolutionary biologist/primateologist speculated that the human language was not due to any neuroanotomical feature, but due to the physical structure of the larynx. He noted that while many modern non-human primates can be trained to use non-verbal human language to some degree of proficiency, none have much facility at producing human speech – their voiceboxes are simply not shaped correctly for it, no more than a cat or dog’s. Modern Apes and monkeys have a poor ability to imitate sounds in their environment – as a group, birds are much better at it. He went on to point out that the extraordinary utility of the human larynx may be due to the elongation it underwent as part of the change in cervical anatomy that went along with adopting a permanent upright posture. In short, early hominids evolved an upright posture for one purpose (eg: seeing over high grass), with the side effect that it enhanced their vocal abilities, allowing mimicry, and eventually, language of a sort.

 

By the time H.Sapiens appears, though, there should have been many hominids with advanced vocal abilities, including the newly speciated H.Sapiens. Why H.Sapiens continued, until very recently, to live like the other hominids, rather than like modern humans, can’t be explained only in terms of their capacity for language use. Some neurological advance seems necessary, such as the one Lahn is hypothesizing.

[Buffy]

I’d be more moved to agree if the ice ages had effected all H.Sapiens-populated places on earth, but they did not. Since the speciation into H.Sapiens 300-400KY ago, it appears there’s never been less than a sizable population of them/us in a place hospitable to the development of modern agriculture, and all the rest of modern human culture. The only conclusion I’m able to draw is that the innovation didn’t occur because H.Sapiens was somehow incapable of it.

The thing that makes Fish's reference to gradualism/PE relevant to this is that while the "speciation" into anatomical h. sapiens may have been at 400kya, the "evolution" of *language* between "expressive grunting" (which probably did have a significant environmental advantage for h.sapiens) and conceptual communications probably did take up a lot of othe intervening 350k years to dominance by sapiens and their "extermination" of h.neandertalis and h.florensis and the other hangers on that we now know lasted until a few 10kya, and the conincidence with severe Ice Age around the same time probably combined to finalize this "change in equilibrium." Not all of our evolution is physical, and the gradual growth in brain size within h.sapiens is probably significant, but "inconclusive" evidence of "speciation."

 

I've really come to appreciate the notion that "speciation" is in the eye of the beholder...

 

Cheers,

Buffy

[CraigD]

… I must wonder if humans brains enlarged & then they built cities & tended crops, or if humans grew crops, built ciites & this "caused" their brains to enlarge? …

My guess is the former, and that probably a good bit of time passed between the neurological change and the city building and crop tending. There are, to this day, numerous genetically modern humans living in cultures that never developed cities or crop-tending, or animal herding, who are not significantly intellectually different than any other group of humans.

 

If city building and crop-tending was something that any primate could stumble into under the right conditions, I’d expect there to be some evidence of another primate species having done so in the past few 100 KYs, but, with the arguable exceptions of Neanderthals and a few hominid species that may have been either befriended or enslaved by H.Sapiens, there just doesn’t seem to be.

 

Of course, paleoanthropology is an iffy, haphazard science. 30 years ago, there was no evidence of H.Sapiens living cooperatively with other Hominids, now there are several, including the recent, spectacular H.Floresiensis “hobbits”, the sites of which some believe show H.Floresiensis (believed to have evolved from H.Erectus) living alongside H.Sapiens ca. 12,000 years ago. Someone might dig up the remains of a great H.Erectus Giganticus city tomorrow, throwing all this speculation stem-over-stern.

 

Keeps it exciting, eh? :hihi:

[HydrogenBond]

I believe that consciousness can manipulate and evolve the DNA. For example, if one thinks about food one can feel hungry. If one traces the biochemistry cascade going on due to the thought of food, the genes within certain cells will unpack, increase RNA transciption, protein translation leading to increased enzyme activity to generate the chemical train need for the instinctive potential. I could see nervous impulse changing the DNA in male and female gamete cells. This is probably why population growth comes primarily from poor people. Their limited world allows more unused nervous potential to be available for gamete cell DNA modifications.