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A few readers reminded me of the recent Rachel Caspari article in Scientific American, The Evolution of Grandparents. It’s actually based on her earlier research, published in PNAS in 2004, Older age becomes common late in human evolution. I was already pointed to this paper by Milford Wolpoff, who seems to be of the opinion this is a very underappreciated dynamic in our species’ history (note: he’s married to Caspari). And Wolpoff sent me a copy of the Scientific American article too, so it’s been in my “to read” folder for a bit.

Honestly it’s a lot more persuasive than the scientific paper because it’s so non-technical. It really makes me appreciate the power of science communication. I don’t know anything about the analysis of dental remains, so I really hummed along through a lot of the paper with minimal comprehension. With the article Caspari could present her results and interpretation more cleanly.

The major finding in the PNAS finding, which is reported in the Scientific American article, is the ratio of parents to grandparents in a total sample of ~750 remains separated by population class varies a great deal. Parents here means those who are 15-30 years old in age, and grandparents are those who are 30+ years in age. The major qualifier here is obviously potential, but that’s a side issue. What the authors found in their sample was quite striking: notice the huge qualitative shift when you move to a population set of Upper Paleolithic behaviorally modern humans (less than 50,000 years before the present). In contrast, the European Neandertals much more resemble the larger collection of archaic Homo (most of which would presumably have been termed “archaic H. sapiens” in the past because they span 50 to 150,000 years B.P.). This still leaves the question of whether this is nature or nurture is left hanging.


But in the Scientific American article Caspari reports a further set of results from another sample: West Asian anatomically modern humans and Neandertals (this sample spans 40 to 110,000 years B.P.) The major finding is that both populations tended to cluster together in their ratios, which were lower than Upper Paleolithic Europeans. The implication that Caspari draws is that the change was not one of biology, because West Asian and European Neandertals would presumably form a monophyletic clade against West Asian and European anatomically modern humans (the tree would have four branches, with two sets of two). And yet on this particular trait behaviorally modern humans are particularly distinctive, and the two West Asian populations are next in line. The authors’ ascribe this to the milder climate of Western Asia, but as a Malthusian I think we need to be careful of this sort of conclusion. It may be that environmental variables are the biggest factors in long term population structure, but just as often intra-specific competition driven by scramble for scarce resources is also a major factor. Did the peasants of the lower Yangtze live a richer and easier life than the nomads of Mongolia? Because the density was so much greater in the lower Yangtze the reality is that there wasn’t that much variance on the margin of subsistence.

Personally I am not that convinced that these results confirm a cultural origin for the change in ratios. They are certainly consistent with it. But one could suggest that a gene of rather large effect swept across human populations, introgressing across distinct lineages. Ultimately this is where genomics may have some utility. Once we have some solid biology around the grandmother hypothesis we may be able to compare the genetic architecture of hominin lineages which we know from ancient DNA.

Overall Rachel Caspari presents to me a entirely reasonable case for a series of positive feedback loops being triggered by a change in the age ratio structure of human populations. But I think it is just as likely that the change in ratio was an effect of some other cultural or biological innovation. This change was what resulted in various knock-on effects, which might include the rise of elder wisdom, the ratchet-process of rapid cultural evolution, and accumulation of skills.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Aging, Anthropology, Culture, Human Evolution 
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ProjectAiko2007BOne of the podcasts I subscribe to is Thinking Allowed from Radio 4. The most recent one was on the role which robots are envisaged to play in the future of Japan:

Also, the rise of the ‘fembot’. The Japanese government is investing billions in the development of robotic technology. They think the robot will do for the 21st century economy what the automobile did for the 20th. However, Jennifer Robertson thinks that as female robots are developed to perform some of the functions traditionally performed by women, it bodes ill for the future of Japanese society.

The guest was very negative about Japan’s plan to substitute robots for immigrants. Basically, she perceived that there was a risk that the Japanese were going to turn into technologically enabled inward-looking xenophobes, closing themselves off to the rest of the world and interacting only with their robot minions. If so, it’s their right as a nation to do so, and I don’t see why all nations should adopt the same policies in regards to globalization. It isn’t as if Japan’s Human Development Index was similar to that of North Korea.

Though science fiction has a generally bad track record as prediction, I couldn’t help but think of Isaac Asimov’s Spacer society of Solaria, from his Robot Series. There’s already a fair amount of media reports about antisocial personality disorders becoming very common in Japan, the sort of stuff that Asimov describes as normal on Solaria. Here is Wikipedia description of the Spacer worlds, of which Solaria was the most extreme case:

In Isaac Asimov’s Foundation/Empire/Robot series, the Spacers were the first humans to emigrate to space. About a millennium thereafter, they severed political ties with Earth, and embraced low population growth and extreme longevity (with lifespans reaching 400 years) as a means for a high standard of living, in combination with using large numbers of robots as servants. At the same time, they also became militarily dominant over Earth.

In many ways the Spacers, and what Japan aims to become, seems to be the realization of what the ZPG movement was pushing for in the 1970s. I’m moderately skeptical that they can pull it off as a practical matter, projections of the feasibility of humanoid robots have been overly optimistic for decades, but it would be an interesting development for a nation which prides itself on its peculiar distinctiveness to be the first to “merge” man and machine into a social ecology.

Image Credit: Wikimedia

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Aging, Culture, Japan 
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Of Moose and Men: 50-Year Study Into Moose Arthritis Reveals Link With Early Malnutrition:

“As the study entered its second decade there was increasing evidence of Osteoarthritis (OA) in the moose population,” said lead author Rolf Peterson from Michigan Technological University. “OA is a crippling disease and is identical to that found in humans. It is commonly believed to be caused by ‘wear and tear,’ but the complex causes have remained poorly understood.”

Over the course of the study the team discovered a rise in OA as the moose population increased, and a decrease when the population fell, leading to the idea that OA is linked to moose malnutrition when food is scarcer. The team found moose that were malnourished when young would develop OA in older age.

“We have shown how malnutrition early in life increased the risk of OA later in life, but this also applies to humans as much as to a herd of moose in the wild,” said Peterson.

“These findings cast new light on how early humans first developed OA,” said co-author Dr Clark Spencer Larsen, an anthropology expert from Ohio University. “The study of human remains from archaeological contexts reveals OA increased where societies changed from foraging plants and animals to an increased dependency on farming.”

Such changes were documented in a mid-continental population of Native Americans 1000 years ago. In this group arthritis increased by 65% as society turned from foraging and hunting to agriculture and the cultivation of maize.

“Initially the increase in OA was put down to increased joint stress due to the labour of agriculture. However research now shows that, like the moose in Isle Royale, nutritional deficiencies early in life may have been the main cause. Early malnutrition was certainly a part of existence for many pre-historic human societies, and remains a fact of life for millions of people across the world, so this study is also relevant for modern human society.”

The original paper is in Ecology Letters, and it should be online at this address. I do wonder if more detailed understanding of the long term impact of early life nutrition is going to drive parents crazy with alarm as every new study which comes out produces a shift in recommendations.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Aging, Medicine 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"