Not exactly. I don't have a clue about cortex, nor do I particularly care about it as a topic of conversation. My comments were referring to the article, whose author seems to find it very significant. Apparently he thinks that it is not merely the presence of grey cortex or white cortex, but the certain features of the "networking". From the article:
(The theory is based on the idea that maximum brain function requires a high level of interconnectivity among brain neurons but a low level of delays in the time it takes for signals to move through the brain. Gray matter contains neuron somata, synapses, and local wiring, such as dendrites and mostly nonmyelinated axons. White matter contains global, and in large brains mostly myelinated, axons that implement global communication...What is the evolutionary advantage of such segregation? Networks with the same local and global connectivity could be wired so that global and local connections are finely intermixed...Brain functionality must benefit from higher synaptic connectivity, because synaptic connections are central for information processing as well as learning and memory, thought to manifest in synaptic modifications. However, increasing connectivity requires adding wiring to the network, which comes at a cost. The cost of wiring is due to metabolic energy required for maintenance and conduction, guidance mechanisms in development, conduction time delays and attenuation, and wiring volume.)
This piqued my interest, because the interconnectivity / signal delay time also come up as engineering tradeoffs in designing and programming parallel supercomputers, for anything except "embarassingly parallel" problems.
Assuming for the nonce that the quotes in the article are accurate, it appears that in humans one of the characteristics that differentiates grey from white matter is the quantity of global vs. strictly local connections between the brain cells. Is this true for all grey/white matter, or is the difference especially pronounced in humans? In other words, is this synaptic differentiation already present everywhere, and we just notice it in humans 'cause our brains are so much bigger than many other species? Or, is the difference in grey and white matter much more pronounced in humans?
If the second, then is the amount of differentiation smoothly varying from lower primate to higher primate up to man, or are there discontinuties, a "step function" in complexity at one or more points?
Are you talking about the time to transform a chimp-like brain into a human one? We have very good fossil evidence this transformation happened within 5-7 million years with most of it in the last three million. A chimp-like creature is a pretty good starting point from which to go in a human direction.
We have the skulls, but not the brain tissue, so unfortunately we can't dissect their brains to look at the degree of axonal connections, or axonal specialization, within different regions of the cerebral cortex. Sigh.
The point being, if you say, we have the fossils, so evolution MUST have done it, but without details of the mechanism, sounds like the "Energy makes it go!" from Feynman which I quoted earlier... The reason I say that is this. So far no one I've seen on this thread has come up with a specific set of environmental conditions, or changes, which would so strongly favor such large changes in intelligence over such a relatively short time. If we happened to know the details of the "engineering" details of the other primates, or (per impossible(*), the transitional forms, we might have a better idea of what specific changes were going on, and be better able to correlate them with the environment. Also, if we knew the exact genetic changes required to code for these changes in the brain, we could look at the number and location of the changes involved, and compare them to the basic mutation clock for DNA, to see if there was any "monkey business" (an outlier) going on.
If, OTOH, we just have the skulls and a few other indications, but we don't know in detail a physical mechanism, or a reasonable, specific set of environmental changes which would select for this growth without eliminating or supplanting related species (+), then just say, "we're not sure how, yet." We're all big boys (and girls) here; there was sufficient evidence (stoichiometry, conservation of mass, etc.) pointing to the atomic theory even before quantum mechanics was fleshed out.
Cheers! (*)[but you never know given the pseudo-fresh dinosaur bones :-) or the preservation of fresh-frozen mammoths :-) wink nudge semi-joking]
(+) If one assumes that the hominids leading up to homo sapiens shared geographical settings with the other primates, one might wonder whether such a huge survival advantage as conveyed by large brains would by mechanisms analogous to punctuated equilbrium supplant the "dumber" members even of other species. Three counterexamples to this supposition might be--first, that the humans were not in direct competition with many of the other primates, as their diets and specific environmental niche changed (humans don't live in trees and tend to hunt larger game); second, that humans originally eliminated some competing species within their environments , but not all; third, that humans eliminated some species, but then moved on, and the geographical areas which were originally denuded of competitors to humanity have been "back-filled" over time as humans moved on...
If one assumes that the hominids leading up to homo sapiens shared geographical settings with the other primates, one might wonder whether such a huge survival advantage as conveyed by large brains would by mechanisms analogous to punctuated equilbrium supplant the "dumber" members even of other species. Three counterexamples to this supposition might be--first, that the humans were not in direct competition with many of the other primates, as their diets and specific environmental niche changed (humans don't live in trees and tend to hunt larger game); second, that humans originally eliminated some competing species within their environments , but not all; third, that humans eliminated some species, but then moved on, and the geographical areas which were originally denuded of competitors to humanity have been "back-filled" over time as humans moved on...
A couple of points here.
First, there is the possibility that the larger brain did not evolve for intelligence as much as for better memory. Persistence hunting requires more memory than plucking fruits off the trees.
This leads into the second point. If the human-ape split began with a savanna group separating from a forest group when the forests contracted, with the savanna group changing in favor of hunting, then there is no direct competition for resources as (1) the territories are different and (2) the resources exploited are different.
Given this scenario, the real selection pressure would be on the savanna group, trying to make a living in a new territory. For the forest-dwellers it was business as usual.
Some posters ask why, if we descended from apes are there still apes? This scenario also addresses that question.
Note that what I am doing contradicts the oft-repeated charge that evolution (just like "Goddidit") predicts everything and explains everything. Under evolution, some things are a heck of a lot more likely than others. It's a far tighter hypothesis which might have been falsified in late 1859 or early 1860 but has not been yet.
For instance, the tree of life has to be a continuous, unbroken tree of common descent. Certain life forms have to have existed, whether we have found them in the fossil record yet or not. By comparison, creationists wave gaps around as evidence for separate creation, but finding yet another fossil filling a gap means nothing to a creationist except that now there are two gaps, one on either side of the new one.
The point being, if you say, we have the fossils, so evolution MUST have done it, but without details of the mechanism, sounds like the "Energy makes it go!" from Feynman which I quoted earlier...
The fossil record won't give you molecular data on anything back very far. You can say what the cranial capacity is by such-and-such a time, size of the Broca's area, etc. You may have some evidence for tool-making, ceremonial burial, or not. But you have extant branch tips and their molecular differences, so it's not a total loss. I see no point in not studying what you have because of what you don't.
Also, it's pretty crazy to pretend something didn't happen because you can't reconstruct exactly in a mutation-by-mutation historical scenario how it did when you have quite a lot of evidence that it did, a general theory of how such things occur, and evidence that evolutionary changes have happened repeatedly and are happening now.
Perhaps you did not realize that cortex is gray matter and your brain stem, medulla, spine, and peripheral nerves are myelinated white matter. The article mangled by C-E Headlines would appear to be about what pressures might drive the evolution of such a feature.