Evolution: more genomic evidence of pre-planning Part One (Evolution)

by dhw, Friday, April 09, 2021, 08:20 (1110 days ago) @ David Turell

dhw: I didn’t make it up, and the point should be perfectly clear to you. There was no huge leap, so please stop insinuating that I am fiddling the figures (“unfair play”). We can now move on to function:

DAVID: There was a huge leap, despite your byplay in numbers. The bold in unfair play:

QUOTE: According to research cited by scholar Richard Lynn, Homo erectus emerged 1.7 million years ago with an average brain size of 885 cc and by 200,000 years ago, their brains had increased to 1,186 cc. How does this compare to modern Western brains? Data from scholar J.P. Rushton shows that Caucasian enlisted men in the U.S. army have a mean cranial capacity of 1468 (Standard Deviation (SD) = 91) and for Caucasian women the mean and SD are 1284 and 90 respectively. From here it can be deduced that a sex-combined sample (that was 50% men, 50% women) would have a mean and SD of 1376 and 137 respectively.

DAVID: US Army comes from all parts of the population and Caucasian women are representative of sapiens. In men: 1,468 cc-1376 cc =s 96 cc extra you blithely ignore.

You have "blithely ignored" the fact that an average is the figure between the highest and the lowest. The women were 1284. 1468 + 1284 = 2752, giving an average of 1376, which is not far off the average of 1350 generally recognized as the average capacity of the sapiens brain. However, this is confusing, bearing in mind shrinkage, which led you to make a statement you have "blithely ignored":

DAVID: “Our current brain averages 1,200 cc+, so our enlargement is at 20% of the last size, quite a huge addition for a previous one lasting a couple of million years”. And then you "blithely ignored" two other statements:

QUOTE: "The brain capacity [of erectus] was between 900 and 1200 cubic centimeters.."

How does 1200 cc provide a 20% enlargement of 1200 cc?

QUOTE: "The upper part of the maximum estimated range for H. erectus endocranial capacity (1,200 cubic cm) thus overlaps with the lower values expected for Homo sapiens."

Even if there is some confusion over the figures, there is simply no point in making the bald statement that there was a huge expansion of 20%, especially bearing in mind that erectus’s expansion was 33%.

DAVID: We agree brains enlarged. Your point is from need, but you have never explained why need produced more expansion than needed at the time point of expansion.

I don’t know how often you want me to repeat that the initial requirements did NOT produce more expansion than needed at the time! That makes no sense! The new requirements would have triggered the expansion needed for their fulfilment and no more than that. From then on, either there was stasis (no more special requirements) or additional requirements could be dealt with by complexification until more cells were needed. That would explain erectus’s expansion, but as sapiens could not expand any more, the brain’s powers of complexification took over. And complexification proved so efficient that previously essential cells were no longer needed (shrinkage).

You have now kindly provided us with three articles, all of which confirm that earlier expansion took place in the same areas with the same functions as our own. I will edit the various quotes:

EDITED QUOTES: Cranio-cerebral topography reveals that the earliest members of the genus Homo had a primitive frontal lobe organization. […] Endocranial shape change associated with frontal lobe reorganization reveals differential expansion of the inferior prefrontal cortex and also of the posterior parietal and occipital cortex. (dhw’s bold)

QUOTE: In modern human brains, the inferior frontal lobe is an important neurofunctional substrate for advanced social cognition, toolmaking and tool use, and articulated language. We may thus ask whether its evolutionary reorganization around 1.7 to 1.5 Ma was accompanied by major changes in technocultural performance.

The answer is that they were, and any of these could have triggered the expansions.

QUOTE: We hypothesize that this pattern reflects interdependent processes of brain-culture coevolution, where cultural innovation triggered changes in cortical interconnectivity and ultimately in external frontal lobe topography. [dhw’s bold] On the other hand, the cerebral innovations that characterize Homo at ~1.5 Ma might have constituted the foundations of the “language-ready” brain of later Homo species. [David’s bold]

You could hardly have a clearer confirmation of the process I have been describing. The brain did not expand or complexify in advance of innovation: the changes were triggered by innovation. And the brain changes would have progressively led to the language-ready brain – not just of sapiens but of earlier homos, as confirmed here:

QUOTE: "Terrence Deacon proposed that the frontal lobe is the developmental and cognitive key to human language ability. If so, frontal lobe expansion implies that hominid language abilities may be quite old, perhaps predating the toolmaking abilities that appear in stone artifacts at least 2.4 million years old.

Please note the expansion of the frontal lobe in hominids. (Continued in Part Two)