And with what hat will you protect a large head, for overheating...

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Can someone please explain this passage to me, 'The “mating mind” sexual selection hypothesis seems at odds with this density effect, and with the more general fact that polygamous species tend to have smaller brains.' My intuition is that the density effect would accelerate brain growth if big brains are sexually selected for, as it would provide more mating partners for the largest brained males.

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Part of the extra complexity in sex is because people didn't (neither would I) trust that people said to *not* share a father really don't; so imposing extra distance on the female line and/or extra physical distance helps avoiding procreation between too closely related people. Might merely avoiding sex between people who share a mother or a (nominal) father result in too many paternal half-sibling pairs reproducing?

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This is not about size, how you use the head makes sense...

The Question remains; when you start using celbrain memory did there already others used the so called brain cape-abillities.

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Regarding Trivers, close but not identical. Trivers says that deception—its commission and detection—was a driving force in human intelligence. Robin's rule-bending overlaps Trivers's deception, but they aren't the same.

As forms of intelligence, they also seem distinct: the lawyer's intelligence (rule-breaking) or the businessman's (deception). Which is _basic_? Robin says the lawyer's intelligence (evading equality norms); Trivers says the businessman's intelligence (gaining advantage in market pricing transactions). But does either account seem adequate?

At lot may be at stake in resolving this nuance.

[Added. Sept. 16] Are these legalistic operations hard enough and intelligence-demanding enough to drive humanity's intellectual development. Deception and finding ways around rules doesn't seem to characterize the most intelligent persons. (Trivers does show that the intelligent lie more, but still, the smartest aren't the most dishonest.)

A weak clue is that lawyers do not seem to be among the smartest people on the planet.

How about this guess: Intelligence was driven by signaling: not that intelligence served as a signal of good genes but that intelligence conferred the ability to signal with greater subtlety. This at least corresponds to (my) observation about intelligence: the smartest aren't the most dishonest or even the shrewdest, but they are the most subtle signalers (in self-promotion [market-pricing]; in signaling affiliation (communal-sharing), the more blatant the better.

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"Over the last two million years hominid brains grew more where climates were variable, but they grew most where population densities were high.  This suggests that human brains were also big mainly due to social pressures."

Something I read in a genetics paper today suggests an alternative explanation:"Conceivably, lineage-specific accelerations and decelerations of evolution can be caused by changes in the effective population size, and such rate changes are indeed expected to equally affect all genes in evolving genomes."

If this is true, then even if the selection pressure for larger brains were constant throughout our evolution, we would still expect to see brains grow the most when populations are the highest.

(from "Universal Pacemaker of Genome Evolution", Snir et. al PLoS Computational Biology 2012)

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The psychological scars, distortions and delusions from this era are still with us;

* nighttime raids by wilders on the domesticates territories and shelters have induced in them an almost phobic fear of the dark - to the point that they have come to imagine or see "things" in the night, and they can experience a peculiar type of dream - the nightmare.

* the wilders are not only subject to the normal pressures and vicissitudes of life, but are also excluded from the best and most secure territories. Everything is "against them", and the survivers develop an odd sense of irrational or overtly positive thinking - they exhibit optimism bias. Depression, or a failure to retain this inflated sense of optimism is a quite common afflication, resulting in ostracization or even abandonment by the community. On the contrary, signs of confidence are highly rewarded.

* Detection of individuals group membership is paramount to safety, to the point that both groups, especially the domesticates, become extremely aware of subtle differences in the two groups physical appearance, build, odours, and voice. They become more and more racist, as a survival mechanism. The apartheid social arrangement is indeed resulting in two (or more) races evolving. Sex or trade between the two races is forbidden by the domesticates, but allowed by the wilders. Breaches of the ban sometimes result in blackmail attempts by the wilders, which in turn results in retribution by the domesticates.

Millions of years into the future, and ... farming develops. It is fairly well accepted now that the early farming era resulted in a decline in the standard of living of farming communities.http://www.sott.net/article...What could have caused this? Why would communities have accepted a social arrangement that resulted in lower nutrition levels all round, compared to the hunter-gatherer lifestyle? In contrast to an economics/demographics explanation like that of Jared Diamond, consider this alternative;

The invention of farming was an attempt to recreate or maintain the social structures of earlier periods of human history, by replacing privileged, domesticated humans, with privileged, domesticated animals.

Farming is an attempt to replicate the social heirarchy and divisions - the constraints - under which certain early human groups evolved. Brains work best when, and in fact gravitate towards situations that are most analogous to the constraints they evolved under. The elevation of animals to the position previously held by the domesticates with simply the outcome of genetic brain wiring, not a carefully considered, rational plan to improve lifestyles, that went wrong. This explains, in some sense, why;

* people stopped being nomadic - the stationary nature of farm animals mimics the superior real estate claimed, occupied and defended by the domesticates.* animals in many ways had higher status than humans - "scared cows".* the loss of the higher race - the domesticates - created a vacuum , a destructuring of social order, that had to be replaced with an alternative structure of the imagination - religion.* the early gods were mostly animal or part animal - reflecting the higher status of animals.* the decline in the standard of living of early farming communities mirror the degraded standard of living of wilders vis-a-vis the domesticates. This perverse outcome is a means of retaining social disadvantage.

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If the social hierarchy includes not only better access to females and food, but is extended to prefered land also, then eventually the hierarchy exceeds its capacity to regulate - social disadvantage overwhelms the system, leading to a break down into competing groups. The difference between rich and poor can become too great to hold the society together, so it splits. What had been the insiders become a secure and slightly domesticated group, and the outsiders become wild and resourceful. Its resources against wits - at the margin.

A problem for the ruling domesticates is that there is an ongoing danger of low status domesticates defecting, to become high status wilders. This is managed by doing something very unusual for almost any mammal - they offer alms to the low status members, rather than discarding them when they become sick or incapacitated. They invent social and medical insurance, for their own benefit. Social insurance prevents defection to alternative social groups. (A reverse of this situation somewhat, occurs in the movie Sicko, when Michael Moore takes Americans across the border to receive treatment in a Canadian hospital.)

Another problem is knowing who belongs in what group. There are no obvious signs of group membership. There are not many good status symbols, nor clothing, coats of arms or flags. Rich signalling mechanisms, like language, are selected for.

At the border of the two groups there are all sorts of interesting dynamics going on, like deception, rudimentary gossip, bribes, blackmail, hostage taking, and more positive traits like trust and reputation. The group borders are relatively vague, as the hunter-gatherers have not yet invented villages, but the demarcation of territories with markers becomes the earliest use of symbols and private property. Here might be the earliest signs of the near-far thinking modes distinction.

The domesticates lead a relatively safe lifestyle, living as they do near sources of fresh water. This provides them with safety from most predators, drinking water, fish to eat, hydration for plants and an opportunity to clean. The wilders prefer to catch, cook and eat meat, but are not so clean. The domesticates find them a little bit disgusting.

The struggles from this era become cultural themes that survive to this day.

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Julian Jaynes argued that to deceive, one first needs a strong concept of self. Who is doing the deceiving? If a strong self concept requires a big brain, you are again left with the problem of cause and effect. Why evolve a sense of self in the first place?

Another way of looking at this is that rule bending, or undetected rule evasion, is about breaking security, which itself requires high intelligence to conceive and apply. So perhaps the big human brain is partly a result of a security arms race. Maybe that is way James Bond is so sexy (nor lumbered by political correctness)?

Domesticated animals are secure, almost by definition, and therefore don't need big brains (so much). Wild animals need bigger brains. Wild animals that are trying to break the security of secure domesticated animals, need bigger brains again, and therefore domesticated animals being attacked by wild animals need bigger brains than otherwise, and therefore wild animals attacking relatively big brained domestic animals need bigger brains yet again, etc.

So who were these groups in early human evolution, respectively? Maybe the domesticated were those near the security and fertility of natural water sources, and the wild ones were low status types pushed into more marginal territories, from both a predator and food & water supply point of view.

Is it all about war?

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Cuddlefish as chameleon may be much more closely related to humans than any species by virtue of its large brain, and its adaptability to any climate, and any cultural exposure - for survival.

While brain size may be accidental, it is logical to be evolutionary in response to the need for adaptability much as that famous fish highlighted on the new PBS series - with corresponding ability to mezmorize prey in much the same manner.

Has mankind found its most closely related species in an underwater correlation?

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The weak jaw muscles idea fits with the Catching Fire idea (softer cooked food), but not of course if fire came later...

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Speaking of brain size, you may be interested in this article: http://www.sciencentral.com...

All humans have a gene defect which causes our jaw muscles to be about the quarter size and strength of apes - apes do not have this gene defect. The hypothesis is that our ancient descendants with the gene defect were able to grow larger brains. Interesting to say the least.

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I don't know that we should, I just didn't think we should expect it not to correlate with density. I took "at odds with" to mean something stronger than you apparently intended.

Tim, yes Wrangham divides brain expansion into a number of advances rather than one continuum. He does think diet (shift to roots/tubers, more hunting for meat and various ways of preparing raw meat) played a significant role in such expansions before fire.

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It's pretty close to standard sociobiology (Trivers, Dawkins, Alexander, etc.).

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Oops - I was mistaken - had another group in mind.

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!kung foragers


!kung nomadic

both yield multiple assertions that they have (or at least had) these lifestyles. Perhaps you are saying that they weren't practicing these ways pristinely when they were studied by the worker I cited?

By the way I wouldn't deny that delicate work surrounding 'iffy acts' could be important, but I think the components of the existing machiavellian intelligence hypothesis seem like they would also be important. Per Wik, de Waal introduced them to chimpology in one of his books, and they include:

" * Making and breaking alliances * making and breaking promises * making and breaking rules; * lying and truth-telling; * blaming and forgiveness; * misleading and misdirection."

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