It is hard to imagine you and me and our neighbors sitting around twiddling our thumbs for 120,000 years - surely we would have carved a bead or two and perfected the spear along the way. But there's no evidence we did anything of the sort until some folks in southern Africa started munching on shellfish. All modern humans are descended from those southern Africans who later migrated up to the Middle East. And anthropologists who followed the trail of our ancestors found the first evidence of widespread consumption and transport of shellfish.
Shellfish are rich in iodine and omega 3 fatty acids. We've discussed the omega 3s at some length, but now let's look at iodine. Iodine is needed to make thyroid hormone, which in turn stimulates the enzyme tyrosine hydroxylase, which is an essential step in the making of dopamine, that neurotransmitter responsible, perhaps, for us being all too human. In addition, the omega 3 fatty acids increase dopamine receptor binding and dopamine levels.
Gagneux et al notes that there appears to have been a huge increase in T3 (thyroid hormone) with the advent of modern humans (chimps, for example, have much higher levels of transthyretin, which binds thyroid hormone and keeps it inactive). It is noted that both chimpanzees and Neanderthals had superficial features in common with developmentally iodine-deficient humans (large femurs, extended brows, and shorter stature). Humans have larger thyroids than chimps, whereas chimps have larger adrenal glands (brain dopamine is essential for inhibiting the systemic arousal caused by activation of the adrenal glands).
Shellfish aren't the only explanation for the rise of modern humans. After all, plenty of animals eat crabs and the like and they don't fly airplanes or...blog. Another (even more speculative theory) suggests that increased human intelligence via marine animal consumption led to longer lifespan, which led to increased populations and increased socialization, communication, and migration. The competitive stresses and achievement drives to out-perform one's neighbor would have plausibly helped to select for brains with more dopamine - though as you may recall there don't seem to be any specific genes for dopamine lateralization. And, once again, we are genetically and physically very similar to our ancestors of 200,000 years ago (except our brains are a little smaller). I'll let Previc explain: "Cultural and dietary influences on dopamine, transmitted prenatally, would have been passed on and enhanced in successive generations and thereby rendered a permanent part of our inheritance. Even when humans moved inland and no longer relied as much on aquatic fauna, their dopaminergically mediated cultural achievements were self-sustaining." It was just around the time of this human mind "Big Bang" that we went through a population bottleneck. All of us are descended from a few thousand people from 65-70,000 years ago - Previc doesn't mention this bottleneck in his book, but the timing is mighty suspicious. It might be that only the humans who were able to fully utilize our super dopamine tracts were able to survive whatever crisis rocked our species back then.
So our ancestors did not need a monolith to spark our leap forward - we needed some clam-digging and crab catching. Iodine and omega 3s enhanced our dopamine-dependent traits - enhanced working memory, cognitive flexibility, the capability of thinking in temporal and spacial distance, creativity, and increased mental speed. This dopamine upgrade in our processing skills enabled art, advanced tool-making, language (not just speech, which seems to have evolved earlier), and long-distance exchange. It made us modern and uniquely capable of wonder and destruction on a scale known only before to nature itself.
Thank you. I enjoyed thinking about what it must have been like 100,000 or so years ago and to be genetically similar to us. Thanks for taking the time to share.
ReplyDeleteWow... what an excellent post and idea! Thanks! I'm really enjoying the dopamine series. I arrived at a similar conclusion from my own readings and I still can't wait to grab the Previc book (been saving up!). Dopamine seems to be humanity's genuine "double-edged sword" and I think understanding the implications of our reward system's design on our actions/afflictions is key. I reckon that a modern 'paleo' approach is ideally one which is 'dopamine-responsible,' especially for those blessed/cursed with one of the more 'challenging' dopamine receptor polymorphisms. ;-)
ReplyDeleteI'd like to put forward a theory based on something I saw on the History Channel's "Becoming Human." The geology of Africa shows an incredibly volatile climate, in which over the course of a 100 years or so, a lake can turn into a savanna, and then 1000 years later, turn back into a lake just as quickly. This climate volatility could have selected for intelligence. Once we developed this intelligence, it was only a matter of time before we were capable of reading tides and collecting shellfish that washed up on the beach at low tide.
ReplyDeleteTo Geoff above:
ReplyDeleteDid you see that part where they found whale bones in the Sahara ? Similar to what you said, in a very short period, about 100 years about 10,000 years ago, climate shifted very quickly and it turns out there was water over the Sahara and the whale bones ? were FROM that era, just very well preserved. I found that most amazing. Also neat is right under the Sahara, and pretty much across the top of Africa ? not far down is one of the world's LARGEST aquifers. Who would have guessed so much water is RIGHT under the Sahara.
Also just to share, I had read of a site in Kandahar Afghanistan that is currently accepted as the oldest known city in the world, it's 10,000 + B.C. and the stones have three tiers: Bird, man, then reptile if you look closely, I noticed that bird imagine shows up in Egyptian and that's what? only 4000 years later. BUT - there is an even OLDER city that has been found, VERY tough to find using google, but it's in North East Africa, dates to 12,000 B.C. and get this - HAS STONE COLUMNS - I have a feeling THOSE people ? migrated west to become the Sumarians or settle by the Nile, which would be one terrific source of fresh water. But I like that pondering there Geoff that climate got us up and moving to figure out a winning model (and what IS evolution but a reach for a winning model I'd think, I mean, evolve to what ? evolve to live I'd think)
Uh oh, maybe trying to live longer as a host of the species denies the species it's ability to function, kind of like a malfunctioning endoplasmic reticulum ? Augh ! We don't really HAVE a view of the human species as living as an atomic whole though, maybe it's better left abstract, I'm not religious, but I'd THINK that's what the real meaning of the 'christos' is, the collective of all human beings, I'm more Darwinian, I like his statement "All life is related" - Odd I derive such a powerful spiritual message from Darwin heh, like Black Elk and chief Seattle say and friends of mine who are Hopi peoples, that life is a web, er the web of life is what my one friend would talk about, and the wheel of life, at the time I didn't pay much attention to it- all seemed new agy to me ! lol... Wow, imagine capitalism with a spiritual component where all humans saw opportunity of being as one giant collective effort to live on forever through the species, instead of some ripoff private afterlife floor plan all self centered... yikes... "But St. Peter, this can't be Heaven, I don't LIKE Aunt Edna, it's going to be hell for me, what do you MEEEAEAN she's here too!" or my favorite "What age will I be if I'm to be just like I was in this form ? and the BULK of that being was that I was mortal" lol... Everyone should engage in some philosophy in academia, and yet ? departments decrease as business departments increase.
neat post though Geoff. Climate may have been our pregame and it just may be our end game, that's for sure. ONly this time ? we're not smart enough to evade global catastrophic climate change, but hey - more oil please is most nation states response ? augh!