February 22, 2010
(This is Part III of a multi-part series. Go back to , .)
Our Story So Far
- It is not enough to state that the availability of high-quality food allowed our ancestors' brains to increase in volume from ~400cc to ~1500cc between 2.6-3 MYA and 100-200 KYA. We must explain the selection pressures that caused our brains to more than triple in size—instead of simply allowing us to increase our population, or to become faster or stronger.
- To gloss over this explanation is a teleological error. It assumes that evolution has a purpose, which is to create modern humans.
Great series, my shirt has been ordered.
I can see this easily going for another three parts, which is great. I notice lots of people tend to view the question of our brains (and really, most things) in too simplistic a light. "It was running". "No, it was definitely fire".
It seems pretty obvious to me it could have been no single thing, so I appreciate how you're taking your time with all the groundwork.
February 22, 2010
Great to see you around again! Wear it with pride.
It's easy to come up with a hypothesis and tell a long, involved story to justify it -- especially at book length, when you can cherry-pick which evidence you present to your readers. It's a lot harder to take all the evidence as it exists and figure out what story it tells.
I have to ask this just for shits and grins. I know you're not hip to the aquatic ape theory, but will you be including anything from "Them and Us" by Danny Vendramini or alternatives theories to the out-of-Africa theory?
February 22, 2010
It's not that I'm not hip to aquatic ape theory...it's that I don't see the evidence that it's true. There's no evidence that Ardipithecus or any other transitional bipedal hominins were aquatic in any way, either in behavior or in diet -- and the fact that the transition to bipedalism preceded the increase in hominin brain size is evidence against it.
AAT is just one of many heterodox hypotheses that could be true...but given the evidence, they're far less parsimonious than the consensus narrative.
Vendramini's hypothesis correctly anticipated the current science (i.e. "mostly out of Africa, with a few percent admixture from male Neanderthals"), and I suspect he's at least partially correct. However, the changes he posits take place 100-50 KYA, after humans had become anatomically modern and reached our maximum brain size, and therefore won't be covered in this series.
Stoked to read more; so fascinating and you explain it so easily. More more more! :)
Got my T-shirt today! :)
It seems this will be a long series and I am hoping to have this in my favorite collections.
Humans are extremely evolved species who could survive on virtually any junk produced in food factories (yeah he does get some nasty diseases :-( ), can run for several hours, can imitate many other animals sound, has very good ability of holding minute items and can pass huge knowledge through generations.
All these requires an explanation and also --
How nature ended up in a super creature which is a big trouble for most of the other species?
June 14, 2011
@Vizeet – "Humans are extremely evolved species who could survive on virtually any junk…".
This is quite literally true and it is an important distinction between 'surviving' and 'thriving'. The impoverished have been known to eat shoes and grass to survive. (Arguably modern foods transit a line of nutrition between these two points, creating food that triggers our 'thrive' senses whilst at a metabolic/physiologic level barely satisfying a 'survive' criteria.)
We might be 'big trouble for most of the other species' but we can't get to anthropocentric about this. Many species have had a dominant period before us and, in time, humans may well be superceded by other lifeforms – perhaps not in terms of intelligence, but better adapted. Don't forget we ourselves are a biome waiting to be exploited!
When beginning to read #3 a question popped into my mind--I'm still at the beginning:
Do you know if animals' brain size increased during the same time period?
February 22, 2010
Thank you! It's a gift I do my best to share.
General-purpose intelligence and breadth of diet usually go together. If you're adapted to eat one single thing, it generally doesn't require intelligence to get it, just instinct -- whereas if you can eat just about anything, general-purpose intelligence helps you find and exploit it. Example: ravens.
The time of anatomically modern humans is vanishingly short by archaeological standards, perhaps 200,000 years so far. The time of hominins is still very short, at perhaps six million years...and recall Part I, in which I compare the 65-million year reign of mammals to the 140 million year reign of dinosaurs.
Given our ability to alter our environment and our current trajectory, we could very easily kill ourselves off in another few hundred years, leaving humans as the biological equivalent of a neutron bomb...200 KYA from inception to self-destruction would be essentially instantaneous when viewed from ten million years hence.
I'm glad your shirt arrived so quickly! Usually overseas shipping takes longer...
The combination of Bergmann's rule and a cooling climate would imply that total body size might have increased during the Pliocene and Pleistocene, but I'm not aware of any data that shows brain size increasing.
Why bigger brains? IMHO there are 3 reasons:
1. Vision - better eyes and better interpretation of the world
2. Hand - manipulating and carrying of tools
3. Speech - development of communication
While 1+2 are good reasons - especially for bipedals, i am sure that 3 had the most influence. And it made culture possible.
See it this way: While 1+2 are simple feedback loops, 3 involves more than one individual! It is much more complex.
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