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March 30, 2012

The tortoise and the tortoise

This week's paper is "Embryonic communication in the nest: metabolic responses of reptilian embryos to developmental rates of siblings", published in Proceedings of the Royal Society by Jessica McGlashan and others.

Turtle eggs deeper in a nest are exposed to lower temperatures. Since they don't regulate their own temperature and since the rate of development depends on temperature, you might expect these eggs to hatch later than those above them. If their older siblings leave first, that could reveal the location of the nest to hungry predators. Some turtle species have solved this problem -- all the turtles emerge together, in contrast to what would be predicted by differences in temperatures to which they were exposed.

The authors of this paper tested the hypothesis that some form of communication between eggs is involved. They exposed eggs to different temperatures, to get different stages of development, then mixed them to see whether the less-advanced eggs accelerated their development when mixed with more-developed eggs.

Mixing with more-developed eggs led to higher respiration rates and heart rates, both of which were measured noninvasively. You might expect that accelerating hatching would lead to problems, but apparently not: the baby turtles were just as good at righting themselves after being turned over.

It would be interesting to compare the question of synchronous emergence in turtles versus germinating seeds. A group of seeds might mostly come from the same mother plant. So, like turtles, they would have fairly high genetic relatedness, which would tend to promote cooperation. But a seed that germinates a little sooner than its neighbors may end up shading them all season. What about turtles? The last turtle to reach the water may have the highest risk of predation, but the first one isn't necessarily safer than those in the middle. Adult trees may benefit from synchronizing their seed production, for predator-saturation reasons similar to those that apply to turtles. But for seed germination, the benefits of being first may outweigh any benefits of synchrony.

March 21, 2012

Cumulative culture and cooperation in humans and other primates

Two recent papers compare the problem-solving abilities of humans and other primates. Individual humans are smarter than individual chimps, of course. But our most-impressive intellectual feats depend on the accumulation of cultural knowledge over many generations. A blacksmith might make some of her own tools, but she didn't invent most of them, or smelt the iron from ore she mined herself. Computer programmers, in turn, depend on technology that built on the work of blacksmiths and many others.

I once read a story in which Earth was visited by aliens with vastly superior technology. Initially, humans assumed that the aliens must be much smarter than we are. It turned out that most of them were pretty stupid, easily duped by humans. It's just that their civilization was older, so they'd had time to invent spaceships and such, even with fewer geniuses than we have. How much of our technological superiority to nonhuman primates is due to superior individual problem-solving ability, and how much to cumulative culture?

"Identification of the Social and Cognitive Processes Underlying Human Cumulative Culture" was published in Science by L.G. Dean and others. They compared the ability of groups of 3-4 year-old human children, chimps with capuchin monkeys, in solving a "puzzle box", where retrieving the most-valued food reward depended on solving three successive levels of increasing difficulty. Only one chimp of 33 got to level 3, while many humans did. Why?

Humans copied others more than chimps or monkeys did. Chimps tended to copy the moves needed to get to the first level, but not beyond that, so it didn't help much to let them see a chimp that had been trained to reach level 3. All 23 clear cases of "teaching" (2/3 verbal and 1/3 via gestures) were by humans. Humans were more generous in other ways also: 47% shared food with others, while none of the chimps or monkeys did. Chimp mothers stole from their own offspring. In summary:

"The children responded to the apparatus as a social exercise, manipulating the box together, matching the actions of others, facilitating learning in others through verbal instruction and gesture, and engaging in repeated prosocial acts of spontaneous gifts of the rewards they themselves retrieved. In contrast, the chimpanzees and capuchins appeared to interact with the apparatus solely as a means to procure resources for themselves, in an entirely self-serving manner, largely independent of the performance of others, and exhibiting restricted learning that appeared primarily asocial in character."
Human adults may be different, however, with rich (or well-educated?) adults acting more like chimps. See last week's post.

The second paper also compares cooperation in humans and other primates. "Old World monkeys are more similar to humans than New World monkeys when playing a coordination game" was recently published by Sarah Brosnan and others in Proceedings of the Royal Society B. Pairs of humans, rhesus monkeys, and capuchin monkeys played the Assurance (or Stag Hunt) game, using computer joysticks to enter their moves. An individual choosing Hare gets a reward whatever the other player does. But if both choose Stag, they each get double the reward.

All of the human pairs talked, but only some talked about the game. Of those that did, all 22 pairs ended up playing mostly cooperatively -- but not 100%, even after seeing the potential benefit. Those who talked about other topics played mostly noncooperatively, forgoing the benefits of cooperation.

The two monkey species differed. For both species, if individuals could see the other's move, they learned to "cooperate" and got high rewards. (They could see each other, but did they realize they were playing with each other, rather than with the computer?) The capuchins played more randomly when they didn't know the other's move, whereas two pairs of rhesus monkeys quickly learned to trust their partner and cooperate (or, anyway, to play as if they did). Rhesus monkeys are native to Africa, rhesus monkeys to South America. So, as the authors put it:

"Old World primates outperformed New World primates,
rather than humans outperforming non-humans."
They speculate that, perhaps:
"...humans' abilities are built on a shared foundation that extends back at least as far as the split with Old World monkeys [which was longer ago than the split between apes and old-world monkeys, let alone the split between humans and other apes]."
An interesting hypothesis, but I would like to see data for more species.

March 9, 2012

Collapse and upper-class greed?

Climate change, adaptive cycles, and the persistence of foraging economies during the late Pleistocene/Holocene transition

Wetland fields as mirrors of drought and the Maya abandonment

Molecular Determinants of Scouting Behavior in Honey Bees

Cultural adaptation, compounding vulnerabilities and conjunctures in Norse Greenland
Kax and kol: Collapse and resilience in lowland Maya civilization

Critical perspectives on historical collapse

Several of this week's papers (in PNAS) revisit some of the examples of societal "collapse" that Jared Diamond's book discussed. I'm looking forward to reading them.

But I want to comment briefly on another interesting PNAS paper:
Higher social class predicts increased unethical behavior." I'm inclined to blame the recent and ongoing global economic collapse -- is that too strong a word? -- on the unethical behavior of some fraction of the upper class. But I don't find this paper entirely convincing, though it's certainly interesting. Here are some of their data.
The top graph shows the percent of cars cutting off other cars at intersections, while the bottom shows the percent that failed to stop for pedestrians, both as a function of subjectively-assessed "vehicle status." It looks like people in high-status cars are more likely to be jerks. (Difference between a Porsche and a porcupine? The pricks are on the outside.) The observers weren't told what hypothesis they were testing, but it seems like it would be easy to guess. Could anti-rich bias on the part of the observers (probably students who weren't rich -- yet -- and who may feel "oppressed" by the rich parents who are paying for their education) have affected their judgment of whether a car cut off another or not? Are "drug-dealer cars" high or low status?

Also, most of the difference in the top graph is between class 4 and 5 cars, while most of the difference in the bottom graph is between class 1 and 2. The paper doesn't comment on this discrepancy. Are all but the poorest (but still rich enough to have a car) jerks against pedestrians, while only the richest are jerks against other cars?

The paper includes results from additional studies, but all were done with undergrads at UC Berkeley. Although some of them came from low-income families, they themselves have a ticket to the upper class. Some might choose low-paying vocations, but at least they get the choice. So I don't have much confidence in those studies.

March 7, 2012

Is diet soda bad for us? An evolutionary perspective.

A recent paper reports that "Diet Soft Drink Consumption is Associated with an Increased Risk of Vascular Events in the Northern Manhattan Study." The correlation persisted even after they corrected for "age, sex, race/ethnicity, education, smoking, physical activity, alcohol consumption, BMI, daily calories, consumption of protein, carbohydrates, total fat, saturated fat, and sodium... and this persisted after controlling further for the metabolic syndrome, peripheral vascular disease, diabetes, cardiac disease, hypertension, and hypercholesterolemia."

Previous studies have found correlations between diet soft drink consumption and other health problems. What's going on? A specific artificial sweetener could have some specific negative effect. But could the sweet taste itself cause health problems? An evolutionary perspective suggests that it could.

Tradeoffs between current and future reproduction (or fertility vs. longevity) are common. Given such tradeoffs, will natural selection favor reproducing now (sacrificing some longevity) or later?

If conditions are good, so that the overall population is growing, it's better to reproduce now, even if that means a shorter life and fewer total offspring. By the time slow-reproducers get around to reproducing, you may be dead, but your many children will be having children.

But if conditions are bad, so that the overall population is decreasing, you may be able to increase your proportional representation in future generations by saving your strength and reproducing later. Even if you have fewer total offspring, you'll be adding them to a much smaller gene pool then if you reproduced before the crash.

So, how do our bodies tell whether the overall population is likely to increase or decrease? If we're eating fruit, rather than leaves, times must be good. But that means the population is likely to increase. So throw the "fertility vs. longevity switch" to the fertility position, whatever the long-term consequences for health.

This hypothesis is consistent with the increased longevity of animals on restricted diets and especially with the reversal of that effect by food odors. I've discussed this in more detail in earlier posts.

One result in this week's paper seems to contradict the "sweet-tasting food is bad for you" hypothesis. however. They found that "there was no increased risk of vascular events associated with regular soft drinks." I think "increased" meant "increased relative to what you would expect from the calories in those drinks." If so, then calories plus sweet taste may be no worse than calories alone.

March 2, 2012

Several interesting papers this week

Chimpanzees' flexible targeted helping based on an understanding of conspecifics' goals

Founder Effects Persist Despite Adaptive Differentiation: A Field Experiment with Lizards

The water footprint of humanity

Identification of the Social and Cognitive Processes Underlying Human Cumulative Culture

Pollinator-Mediated Selection on Flower Color Allele Drives Reinforcement

The Geological Record of Ocean Acidification