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Hey there Big Brains - how do you think it happened

The Human brain is amazing. It uses around 25% of many of our body's metabolic resources (such as oxygen) to operate. This aspect does not, intuitively, seem like an adaptation that would have helped us out if it didn't happen gradually over a long period of time so that the benefits could justify the resource use. But it didn't happen (on an evolutionary scale) over a long period of time.

Its divergence from the slow, expected progress of evolution when compared to other primates' brains seemed to have rapidly occurred over the past 300,000 years or less. This appears to some to defy the basic principle of incremental change over time. Was it was the result of a single mutation - perhaps mitochondrial Eve? If so, a big brain that is uneducated (imagine the first super-genius) isn't as useful as might be imagined. And such a visible mutation might have made that baby a target for destruction by the 'community.'

In any case - I am fascinated by my recent introduction into this aspect of evolution and am hoping people can share scholarly articles and educated insight into this puzzling aspect of evolution. Here's my contribution:

THE EVOLUTION OF THE HUMAN BRAIN:DILEMMAS AND POSSIBLE RESOLUTIONS
By Robert DePaolo

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Replies to This Discussion

Permalink Reply by Kevin Saldanha on March 18, 2010 at 9:54pm

Evolution does not necessarily have to be a slow process. It has been shown that changes can occour in as little as 9 generations if the environmental changes are so drastic that those random mutations allow survival of fewer individuals.

This is probably what happened in early man, the environmental change being one of habitat selection and modification. As early humans were honing their hunting and gathering skills that were pretty much hit or miss for the preceding 6 million years, during which they merely ate off the fat of the land, they were selecting survivors who had better tool making, fire building and team hunting skills than their ancestors. Moving out of their comfort zone required selecting or building shelters against inclement weather, creating clothing, preparing highly nutritious flesh for consumption with heat and co-operating with others for the benefit of the tribe.

So with the new techniques and knowledge came the need to create more synapses and neurons to store and process this new information, literally creating bulbous growths of knowledge which stretched our bony skulls into thin plates to protect the fragile grey matter. It wasn't long after that that language developed and social co-habitation required a whole new skillset to occupy our minds.

Permalink Reply by Howard S. Dunn on March 19, 2010 at 12:03am

True that evolution does seem to offer some 'quantum leaps.' I read somewhere that the last demonstrable metabolic evolution in humans has occurred over the past 8,000 years with the ability to digest bovine dairy products as opposed to ovine products more prevalent in earlier cultures. Apparently, transhumance farming on the slopes of the alps introduced cow's milk in the form of cheese to those in the growing settlements in the river valleys (initially glaciated valleys.) Whereas, in the Mediterranean, goat and sheep's milk and cheese was already in the diet of the newly rising civilizations.

Apparently it takes less time (1000 years or so) to develop distinguishing characteristics we associate with the construct of 'races' - such as changes in hair texture, skin color (melanin density), average height, etc. such that a northern 'race' would develop - without interbreeding - characteristics of an equatorial 'race' simply by relocating and settling in the warmer clime for a millennium or less (and vice versa).

However, the rapid evolution of the brain that results in a 'fractuous' skull in the infant, a drastic increase in resource requirements with little increased benefit initially, since the adaptation would take some time to program - with generations of 'history' to make it as useful as it was taxing - it just seems such a remarkable process of emergence. Perhaps, in this case, it is akin to a snowball effect. Clearly, at some critical point - perhaps, as you say, the ability to plan and coordinate a cooperate hunt - would have given homo sapiens sapiens a drastic advantage.

It may be there was a critical point where we became successful enough - barring disasters such as drought, floods, ice ages, etc. to have free time and develop more abstract intelligence that really started the snow ball rolling down the hill - picking up more mass as it went; so to speak.

I can't wait until the fossil record fills in a bit more.

Permalink Reply by Kevin Saldanha on March 19, 2010 at 5:11pm

... speaking of drought, floods, ice ages, etc...

Interesting free offering from National Academies Press - PDF book for download on "Understanding Climates Influence on Human Evolution"
http://books.nap.edu/catalog.php?record_id=12825&utm_medium=etm...

Permalink Reply by Howard S. Dunn on March 23, 2010 at 3:20pm

Thank you. Yes, I just recently heard an interview with a scientist studying this who contends that surviving climate change is what humans - among mammals - do extremely well. Consider our ability to harness fire, and willingness to wear the skins of other animals, adoption of orphans, etc. Obviously, this trended to much more sophisticated innovations - but you get the picture.

Permalink Reply by Alfred Differ on March 20, 2010 at 1:16am

Both genders select for mates and many of us select on intelligence. It's a positive feedback loop because each must be watchful for mating tricks that merely simulate intelligence. Most species have one gender selecting and the other displaying.

Another possible (not necessarily mutually exclusive) option is that there are actually two replicators in our population. The first and oldest is the genetic one with animal-based selection factors. The second is the memetic one with social/cultural selection factors. With the second replicator driving, our physical characteristics would adapt to a success factor that did not appear to work well biologically.

Permalink Reply by james bunyan on March 23, 2010 at 2:17pm

i think your contention that the human brain suddenly emerged is not quite right, if you look at the skulls we have of other primates in our tree you see a steady enlargement over some 2 million years of the brain cavity in cc's of brain mass inside the skulls so although we only see sapiens with large brain cavity's appear 300, thousand years or so ago, we decend from others with smaller and smaller skulls as you go back in time its not such a quick change after all.

Permalink Reply by Kevin Saldanha on March 23, 2010 at 3:12pm

However, several hundred, thousand years or a few million years is relatively short on a geological timescale... something that many adults have a hard time wrapping their minds around.

I have a game presentation that I have been doing at the local Camp Quest for a few years now teaching kids how important the understanding of geological time is to understanding evolution. Of course we hardly use the term evolution but even the younger kids can understand that SpongeBob SquarePants is actually their cousin!

Permalink Reply by Howard S. Dunn on March 23, 2010 at 3:17pm

SpongeBob is my Sensei!

Permalink Reply by stephanie on April 15, 2010 at 3:12pm

how else could you explain darwinism and evolution without using those terms? i think most people have a tough time realizing that animals (whether mammal or reptile or what have you) are our cousins or distant relative, unless we have that same impression of "being created from the same blanket" or does the word "creation" imply something was responsible in the first place rather than "evolved"? just curious.:)

Permalink Reply by stephanie on April 15, 2010 at 3:13pm

and yes, we study under the same master Spongebob Sensei too!

Permalink Reply by Howard S. Dunn on March 23, 2010 at 3:23pm

Actually - as Kevin points out - there is what is considered a rapid increase relative to the enlargement and capacity of the brains other primates that occurred over a few 100 centuries - not long at all in the scheme of 450,000,000 years of evolution. Keep in mind that this represents what is considered the crowning 'achievement' of evolution to date. (Puns intended.)

Permalink Reply by Howard S. Dunn on March 23, 2010 at 4:23pm

http://www.onelife.com/evolve/manev.html

A little further reference to peruse. Even for me.