It's All in the Mind

How do physiological and molecular variation combine to create a range of motivational drives that becomes manifest as a range of behaviors? Champagne et al. report measurements of dopamine in the nucleus accumbens of female rats caring for (licking and grooming) their pups. This region of the brain is known to contribute to motivating behaviors, particularly those that are followed by reward, such as the consumption of food. The increase in dopamine preceded the initiation of licking and grooming acts by the mothers, and the size and duration of the dopamine signal correlated with the duration of the act. Furthermore, mothers previously scored as high or low in licking/grooming (greater than 1 standard deviation from the mean of a normally distributed group) exhibited consistently high or low scores in the dopamine signal and in the density of dopamine receptors in the shell of the nucleus accumbens. Taken together with earlier studies in this series, these results begin to establish a neurochemical basis for individual differences in maternal behavior.
J. Neurosci. 24, 4113 (2004).

Neurons in the orbitofrontal cortex encode economic value

Economic choice is the behaviour observed when individuals select one among many available options. There is no intrinsically 'correct' answer: economic choice depends on subjective preferences. This behaviour is traditionally the object of economic analysis1 and is also of primary interest in psychology2. However, the underlying mental processes and neuronal mechanisms are not well understood. Theories of human and animal choice1 have a cornerstone in the concept of 'value'. Consider, for example, a monkey offered one raisin versus one piece of apple: behavioural evidence suggests that the animal chooses by assigning values to the two options4. But where and how values are represented in the brain is unclear. Here we show that, during economic choice, neurons in the orbitofrontal cortex (OFC) encode the value of offered and chosen goods. Notably, OFC neurons encode value independently of visuospatial factors and motor responses. If a monkey chooses between A and B, neurons in the OFC encode the value of the two goods independently of whether A is presented on the right and B on the left, or vice versa. This trait distinguishes the OFC from other brain areas in which value modulates activity related to sensory or motor processes. Our results have broad implications for possible psychological models, suggesting that economic choice is essentially choice between goods rather than choice between actions. In this framework, neurons in the OFC seem to be a good candidate network for value assignment underlying economic choice.

Younger Moms' Kids Get Longevity Edge

MONDAY, April 17 (HealthDay News) -- Society's oldest members are most likely to be born to its youngest mothers, new research suggests.
The odds of living to 100 and beyond double when a person is born to a woman under 25 years of age, compared to those people born to older mothers, according to one of the most rigorous studies on the subject yet conducted.
The finding may also help clear up a statistical mystery -- three years ago, the same husband-and-wife team of researchers found that being the first-born child in a family also boosted longevity, although no one knew why.
"It turns out that the whole phenomenon of first-born order and longevity is driven by young maternal age," said study co-author Leonid Gavrilov, a research associate at the Center on Aging at the University of Chicago.
In other words, he said, first-born children are simply more likely than their siblings to have been born when mom was in her teens or early 20s.
The study, which was funded by the U.S. National Institute on Aging (NIA) and the Society of Actuaries, was presented recently at the Population Association of America annual meeting, in Los Angeles.
As nutrition and health care continue to improve, so too does the number of Americans whose years extend into the triple-digits.
"Certainly there were more [centenarians] in the 2000 census than there were in 1990, and most people think this population will grow," said Georgeanne Patmios, acting chief of the Population and Social Processes Branch of the NIA's Behavioral and Social Research Program.
According to the Census Bureau, there were 37,000 Americans aged 100 years or older in 1990, and by 2000 that population had risen to 55,000. According to experts, women are three to five times more likely to live beyond 100 than men.
But what other factors encourage "extreme" old age? Previous research by Gavrilov and his wife/co-researcher, Natalia Gavrilova, has uncovered some clues. For example, in research published over the past few years, they found that U.S. centenarians were more likely to come from farming families in the Midwest than from any other demographic.
They also discovered that being the first-born in a family meant a lot, boosting the odds of making it to 100 by nearly 80 percent.
"But nobody knew why that was -- sometimes in research you get answers, but you also get new questions," Gavrilov said.
So, he and his wife set out to solve that puzzle. They selected 198 centenarians from across the United States, checking and double-checking their ages using every form of documentation available. Comparing the centenarians' histories to those of their siblings, the researchers then analyzed the data to help explain the "first-born effect."
One theory -- that first-born children might have been relatively protected from pediatric illness because they weren't surrounded by disease-bearing siblings in infancy -- didn't pan out. "We found that even at age 75 it still matters that one is first-born," Gavrilov said. "It's a late-life phenomenon."
A second theory -- that first-born kids reaped the benefit of a relatively young, strong and productive father -- also fell flat. "We got the very clear result that the father's age wasn't important," the Chicago researcher said.
That wasn't the case for mothers. In fact, statistical analysis revealed that young maternal age at birth completely accounted for the first-born effect.
"It is very rare in science that you have such clear-cut results. But here, when we saw the results, we went 'Wow,'" Gavrilov said. Overall, children born to an under-25 mother had double the odds of living to 100 and beyond, compared to offspring of women who delivered at a later age.
So, why do young moms tend to bear more long-lived children? "At this point all we have is hypotheses," Gavrilov said. "One is biological -- that maybe the eggs are different in their quality, and the best ones, the most vigorous eggs, go first to fertilization."
He said his wife Natalia came up with a competing theory: That young moms haven't had time to pick up the latent, chronic infections that might in some way impede the long-term health of their offspring. "This might interfere with normal development," Gavrilov said. "So, when the children are born they are superficially healthy but maybe they are not really strong enough to survive to 100."
Patmios said the question of why younger mothers might bear more resilient offspring remains "open, but it's worthy of additional research." She stressed that it has proven extremely tough to get in-depth, reliable data for events that happened over a century ago. "There are a lot of other factors that probably contribute to exceptional longevity which, given the dataset that Dr. Gavrilov has to use, he can't assess," she said.
And what about the longevity of children born to today's moms, who are often postponing first pregnancy to their 30s or even 40s? According to Gavrilov, advances in diet and health care mean American newborns still have a better chance of living out a century than their great-grandparents did.
"The data shows that there is a steady increase in living to age 100, despite the fact that women are tending to postpone their childbearing years," he said.

Cooperation, Punishment, and the Evolution of Human Institutions

Explaining the scale, diversity, and historical dynamics of human cooperation is increasingly bringing together diverse empirical and theoretical approaches. For decades, this challenge has energized evolutionary and economic researchers to ask: Under what conditions will decision-makers sacrifice their own narrow self-interest to help others? Although classic evolutionary models based on relatedness and reciprocity have explained substantial swaths of the cooperation observed in many species, including our own, theoretical work in the 1980s demonstrated that the puzzle of cooperation in large groups, or in situations without much repeated interaction, remained unsolved and would likely require alterative theoretical formulations.

Such cooperative dilemmas, or "public goods" problems, involve situations in which individuals incur a cost to create a benefit for the group. In our society, think of recycling, buying a hybrid car, valor in combat, voting, and donating blood. The dilemma arises from free-riders who enjoy the group benefits created by the contributions of others without paying the costs. Even if nearly everyone is initially cooperative and contributes, free-riders can profit and proliferate, leading to the eventual collapse of cooperation. So, understanding how public goods problems can be solved has provoked great interest, both because human societies have somehow managed to solve many such problems to varying degrees, and because some of the world's most pressing issues, such as global climate change, are essentially public goods dilemmas. On page 108 of this issue, Gürerk et al. take an important step in understanding how self-sustaining cooperative institutions may have emerged over the course of human history.

Recent models have demonstrated how evolutionary processes (genetic or cultural) can maintain cooperation in large groups or without repeated interaction. Costly signaling models have shown how cooperation by "high-quality individuals" (those who are potentially desirable as allies or mates) can be sustained if such individuals can accurately signal their quality by making substantial cooperative contributions to public goods. For example, great hunters might supply all the meat for a public feast, or millionaires might donate a recreational center to their community. Similarly, reputation-based models have shown how cooperation can be sustained if individuals' reputations for not contributing to public goods reduce their payoffs (or fitness) by altering how others treat them in certain dyadic social interactions. Finally, models that allow individuals to both contribute to the public good and to sanction noncontributors have revealed stable cooperative solutions, especially when the strategies for cooperation and punishment are influenced by social learning. Thus, a number of possible stable solutions to the puzzle of cooperation in large groups, or cooperation without repeated interaction, have now emerged.
It turns out, however, that finding a stable solution is only the first step in confronting the dilemma of cooperation. Each of the above approaches can actually stabilize any behavior or practice, independent of whether it delivers any benefit to anyone. This includes behaviors that reduce the payoff or fitness of the group. For example, instead of public goods contributions, costly signaling could maintain behaviors involving dangerous physical feats (like scaling icy mountain peaks), aggressive displays (like beating up your neighbor), or extravagantly wasteful feasts. Similarly, the same reputational and sanctioning mechanisms that can stabilize cooperation can also sustain maladaptive practices such as consuming the brains of dead relatives, flattening the foreheads of infants, or binding the feet of young girls. Thus, there are actually a multitude of stable equilibria, only some of which are cooperative. What determines which equilibria emerge and/or spread?
Three broad theoretical approaches confront the problem of equilibrium selection. The first, and perhaps the most intuitive, is that rational, forward-looking individuals recognize the long-term payoffs available at stable cooperative equilibria, assume others are similarly sensible, and choose the cooperative state. The second approach is based on the stochasticity inherent in any interaction. Different stable equilibria are more or less susceptible to this stochasticity, meaning that in the long-run, some equilibria will be substantially more common than others. The third mechanism, cultural group selection, gives priority to the competition among social groups who have arrived at different culturally evolved equilibria. This intergroup competition favors the spread of individuals and practices from groups stabilized at more cooperative equilibria. In humans, competition between groups can take the form of warfare, demographic production (some social groups reproduce faster than others), or more subtle forms in which individuals learn decisions and strategies by preferentially observing more successful individuals, many of whom are more successful because they live in groups at stable cooperative equilibria. This can lead to a flow of decisions, strategies, and even preferences from more cooperative groups to less cooperative ones, or to a migration of individuals among groups that favors the spread of the more cooperative equilibria.
Gürerk et al. address the issue of equilibrium selection with an elegant addition to the existing experimental work on public goods. In their experiment, individuals (the "players") choose between two different "institutions." In one institution, players can contribute money to a group project. The sum of all contributions to the project is augmented by a fixed percentage and then is divided equally among all players, regardless of their contributions. Previous experiments established that when this interaction is repeated, mean contributions to the public good drop to near zero (a noncooperative equilibrium). The other "sanctioning" institution is very similar, except that after players have contributed, they can pay to punish (reduce the payoff of) other players. When this interaction is played repeatedly a substantial fraction of players punish low contributors, causing mean contributions to rise and stabilize near full cooperation (a cooperative equilibrium). Both institutions were run concurrently for 30 interactions and players could, initially and after each subsequent interaction (after seeing others' payoffs), choose their institution for the next interaction.
The principal findings of Gürerk et al. can be summarized simply. Initially, most players picked the institution without sanctioning possibilities. But, as usual, free-riders in the nonsanctioning institution started driving mean contributions downward, so cooperators, who hate being exploited by free-riders, started reducing their contributions. Meanwhile, in the sanctioning institution, punishers started driving contributions up by inflicting costs on noncontributors, despite the personal cost of punishing. After a few interactions, players from the nonsanctioning institution--presumably seeing the higher payoffs of those choosing the sanctioning institution--increasingly switched institutions. Notably, despite the incoming flow of migrants from the nonsanctioning institution, the mean contributions in the sanctioning institution consistently increased or held stable near full cooperation. In fact, most incoming migrants, consistent with local norms in their new setting, increased their contributions during their first interaction in the sanctioning institution, and a majority administered some punishment.
What does this tell us about equilibrium selection? First, the players' degree of rationality did not permit them to foresee the final outcome and select the higher payoff institution on the first interaction. Second, despite the stochasticity of human decisions, neither institution drifted to another equilibrium. What did happen is that once players from the lower payoff institution observed the higher payoffs of the other institution, they wanted to adopt either the practices of the higher payoff institution, or the decisions and strategies of those other players. Consistent with ethnographic and historical case studies, the present work provides an important experimental demonstration of cultural group selection in action, as the two alternative equilibria compete for shares of the total population.
The course charted by Gürerk et al. should spur more empirical work on how processes of equilibrium selection influence the evolution of institutional forms. Many questions remain to be tackled: for example, what happens if switching institutions is costly, or if information about the payoffs in the other institution is poor? Or, what happens if individuals cannot migrate between institutions, but instead can vote on adopting alternative institutional modifications? Such work can both help us understand how humans became such a cooperative species, and teach us how to build durable cooperative institutions that solve public goods problems and are readily spread.