Progress Daily

Worldwide, 10% to 40% of children grow up in households with no father. In the U.S., more than half of divorced fathers lose contact with their kids within a few years. By the end of 10 years, as many as two-thirds of them have drifted out of their children’s lives. According to a 1994 study by the Children’s Defense Fund, men are more likely to default on a child-support payment (49%) than a used-car payment (3%). In intact U.S. families, fathers spend an average of less than an hour a day (up from 20 minutes a few decades ago) focussed on their children.

Homo sapiens produces the most slowly maturing young of all mammals. Among foraging humans, children need 19 years — and consume 13 million calories — before producing more food for their community than they take from it, according to Hillard Kaplan. There is more variation in fathering styles across human cultures than in any other primate species.

One thing that draws a human male to a child of his is that, hormonally speaking, men are similar to women, during the period approaching a child’s birth and its infancy. As in some other mammalian species, human males have high levels of prolactin (a hormone usually associated with lactating mothers) toward the end of a partner’s pregnancy.

Katherine Wynne-Edwards and Anne Storey have shown that new or expectant fathers holding either their baby or a doll wrapped in a blanket that recently held — and still smells of — a newborn experienced a rise in prolactin and cortisol (a stress hormone associated with mothering) and a drop in testosterone. When the men listened to a tape of a crying newborn and were shown a videotape of a newborn struggling to nurse, the ones who reported the greatest urge to comfort the baby were the ones whose hormone levels had changed the most.

Dads have to spend time close to babies for hormones to kick in.

In traditional societies, 40% of offspring might die before age 5.

Among some West African Mandinka, the help of a maternal grandmother has been linked with a halving of the under-5 mortality rate. Similar benefits were shown in Finnish farming communities in the 18th century.

It was this cooperative system that allowed mothers to have more babies than they could support and fathers to vary in how they cared for them.

“The Psychology of Fatherhood,” by Sarah Blaffer Hrdy

A small study (”Efficacy of physical activity in the adjunctive treatment of major depressive disorders“) has found that depressed women who exercised had significant improvements in their symptoms over the next 8 months. Those who didn’t exercise showed only marginal improvements.

Before the study, all of the women had tried taking antidepressant medication for at least 2 months but had failed to improve.

The study included 30 women ages 40 to 60 who’d been diagnosed with major depression. The researchers randomly assigned the women to either stick with antidepressants alone or to start an exercise program. All of the patients continued to take their medication.

The exercisers worked out as a group twice a week for one hour, using cardio-fitness machines. At the beginning of the study and 8 months later, women in both groups completed standard measures used to assess depression severity.

Women in the exercise group showed marked improvements in their depression symptoms, while those on medication alone made only modest gains.

Physical activity seems to affect some key nervous system chemicals — norepinephrine and serotonin — that are targets of antidepressant drugs, as well as brain neurotrophins, which help protect nerve cells from injury and transmit signals in brain regions related to mood.

“Exercise may help with hard-to-treat depression,” Scientific American

Unremitting stress damages the immune system. Two years ago, researchers at UCSF looked at white blood cells from a group of mothers whose children suffered from chronic disorders like autism or cerebral palsy. They found clear signs of accelerated aging in those study subjects who had cared the longest for children with disabilities or who reported the least control over their lives.

The changes took place in microscopic structures called telomeres, which are often compared to the plastic wrappers on the ends of shoelaces and which keep chromosomes from shredding. As a general rule, the youngest cells boast the longest telomeres. But telomeres in the more stressed-out moms were significantly shorter than those of their counterparts, making them, from a genetic point of view, anywhere from nine to 17 years older than their chronological age.

People with low self-esteem are more vulnerable to stress. According to Jens Pruessner, the hippocampus — a finger-size structure located deep in the brain, which helps you form new memories and retrieve old ones — is particularly sensitive to the amount of cortisol flooding your cerebrum. So when cortisol levels begin to rise, the hippocampus sends a set of signals that help shut down the cortisol cascade.

Using several different types of brain scans, Pruessner has shown that people who test below average on self-esteem also tend to have smaller-than-average hippocampi. (The differences become clear only when you compare groups of people.)

Samuel Melamed: “[I]f there is no relief [from stress] and the cortisol stays up for long periods of time, the body stops responding and readjusts the level.”

If you provide mice with an escape route, they typically learn quickly how to avoid a mild electrical shock that occurs a few seconds after they hear a tone. But if the escape route is blocked whenever the tone is sounded, and new shocks occur, the mice will eventually stop trying to run away. Later, even after the escape route is cleared, the animals simply freeze at the sound of the tone– despite the fact that they once knew how to avoid the associated shock.

Animal research has shown that there is a relatively small window for reversing the physiological effects of chronic stress. And once a person’s cortisol level gets completely blunted, it may stay that way for years.

“6 Lessons for Handling Stress,” by Christine Gorman

Wendy Demark-Wahnefried recruited 161 men recently diagnosed with prostate cancer, which they split into 4 groups.

One group ate 3 tablespoons of flaxseed each day (by mixing it with yogurt or water, for example) and maintained a low-fat diet. Of the remaining 3 groups, one maintained a low-fat diet, another ate flaxseed, and the last was a control that made no lifestyle change.

Most of the men had surgery to remove their prostates within 30 days of enrolling in the trial.

Demark-Wahnefried examined the DNA of the removed tumour cells.

The analysis revealed that 50% fewer of the tumour cells from men assigned to eat flaxseed - with or without maintaining a low-fat diet - were actively dividing compared with those of their control counterparts. Maintaining a low-fat diet alone did not appear to affect tumour growth.

Demark-Wahnefried speculates that replacing omega-6 molecules in the body with omega-3 compounds may send chemical signals that tell cells not to divide.

There are about 4 grams of omega-3 fatty acids in 3 tablespoons of flaxseed.

Demark-Wahnefried notes that flaxseed can have a laxative effect.

“Flaxseed may slow prostate tumour growth,” by Roxanne Khamsi

In the ultimatum game, one player divides a pot of money between himself and another. The other then chooses whether to accept the offer. If he rejects it, neither player benefits. A stingy offer (one that is less than about a quarter of the total) is, indeed, usually rejected.

One explanation of the rejectionist strategy is that human psychology is adapted for repeated interactions rather than one-off trades. In this case, taking a tough, if self-sacrificial, line at the beginning pays dividends in future rounds of the game. (When one-off ultimatum games are played by trained economists they do tend to accept stingy offers more often than other people would.) Terence Burnham recently gathered a group of male students of microeconomics and asked them to play the ultimatum game.

Dr Burnham’s research budget ran to a bunch of $40 games. When there are many rounds in the ultimatum game, players learn to split the money more or less equally. He also ran a game of one round only, in which proposers could choose only between offering the other player $25 (ie, more than half the total) or $5. Responders could accept or reject the offer. Dr Burnham took saliva samples from all the students and compared the testosterone levels assessed from those samples with decisions made in the one-round game.

The responders who rejected a low final offer had an average testosterone level more than 50% higher than the average of those who accepted. Five of the 7 men with the highest testosterone levels in the study rejected a $5 ultimate offer but only one of the 19 others made the same decision.

A high testosterone level is correlated with social dominance in many species.

“Money isn’t everything,” The Economist

In a study of East Asians, Europeans and Africans, Jonathan Pritchard found 700 regions of the genome where genes (some of which are active in the brain) appear to have been reshaped by natural selection in recent times.

In East Asians, the average date of these selection events is 6,600 years ago.

The genetic changes occurred around the same time as the beginning of the Neolithic revolution, when societies switched from wild to cultivated foods, such as rice.

“Since it looks like there has been significant evolutionary change over historical time, we’re going to have to rewrite every history book ever written,” said Gregory Cochran. “The distribution of genes influencing relevant psychological traits must have been different in Rome than it is today. The past is not just another country but an entirely different kind of people.” 

John McNeill said that “human nature is not a constant” and that selective pressures have probably been stronger in the last 10,000 years than during any other epoch.

Oxytocin increases a person’s level of trust, at least in psychological experiments, & these levels are known to be under genetic control in other mammals.

In societies where trust pays off, generation after generation, the more trusting individuals should have more progeny and the oxytocin-promoting genes would become more common. If conditions should then change, and the society be engulfed by strife and civil warfare for generations, oxytocin levels might fall as the paranoid produced more progeny.

Napoleon Chagnon for many decades studied the Yanomamo, a warlike people who live in the forests of Brazil and Venezuela. He found that men who had killed in battle had 3 times as many children as those who had not. Since personality is heritable, this would be a mechanism for Yanomamo nature to evolve and become fiercer than usual.

“The Twists and Turns of History, and of DNA,” by Nicholas Wade

Studies of mice and monkeys show that repeated stress — and a high-fat, high-sugar diet — release a hormone, neuropeptide Y, that causes a buildup of abdominal fat.

Manipulating levels of that hormone could melt fat from areas where it is not desired and accumulate it where it is needed.

Stephen Baker said it could also reduce or eliminate the need for extremely expensive fat replacements used in breast and facial reconstruction and in other surgeries.

Zofia Zukowska divided mice into 4 groups: 2 received a conventional diet, and 2 received a diet high in fat and sugar. Then one group from each diet was forced to stand in cold water for an hour every day, “like the Northern European experience of waiting for a bus with wet feet.”

The remaining groups were exposed to an aggressive alpha male for 10 minutes each day, “like having a bad boss.”

For the mice on the normal diet, “it really didn’t matter whether they were stressed or not. They didn’t have much difference in weight. If anything, the stressed ones weighed less.”

But the stressed mice on the “fast food” diet accumulated twice as much belly fat in the first 2 weeks as those that were not stressed. Over 3 months, they became grossly obese.

Biopsies of the fat showed increased levels of neuropeptide Y, or NPY, a hormone discovered nearly 25 years ago. In the brain, NPY stimulates appetite. In the periphery of the body, it is a growth factor that stimulates enlargement of cells and the production of new blood vessels to supply nourishment.

Zukowska and Lydia Kuo found that the hormone not only enlarged fat cells, but stimulated the production of new fat cells and blood vessels to support them.

A buildup of abdominal fat is a prime contributor to “metabolic syndrome,” which affects 60 million Americans, and sharply increases the risk of diabetes, heart disease and stroke.

The researchers attempted to mimic the process of fat formation by implanting NPY in a slow-release tablet under the skin of mice and monkeys. In each the production of new fat was stimulated around the tablet.

Next, they implanted human fat in nude mice, which have an inhibited immune system and are unable to fight off such transplants. Normally, this fat is reabsorbed by the animal within a couple of weeks. But when they implanted NPY along with it, 99% of the fat was retained after three months.

When the researchers implanted a slow-release tablet of a small molecule that blocks the cellular receptor for NPY, the fat buildup did not occur. Implanting the molecule in a fat deposit caused the fat “to just melt away.”

Within two weeks the fat deposit in the mice had shrunk by half.

The hormone and the receptor are nearly identical in mice, monkeys and humans.

There is a Northern European population that, due to a genetic abnormality, secretes excessive amounts of NPY when stressed. That population is unusually susceptible to obesity and diabetes. In contrast, a Swedish population with a genetic mutation that lessens the receptor’s efficacy is resistant to obesity.

NPY has been injected into humans with no apparent side effects, but its long-term effects have not been studied.

“Stress can be fattening, study finds,” by Thomas H. Maugh II

A study by Michael French looked at 2002 data from a survey of U.S. households representing more than 31,000 adults.

The survey contained questions about alcohol consumption, health behaviors and chronic health conditions. Moderate drinking was defined as 4 to 14 drinks a week for men and 4 to 7 drinks a week for women.

The male participants who reported moderate drinking were 1.3 times more likely to report above-average health, compared with those who were lifetime abstainers and former light drinkers. The moderate drinking women were more than twice as likely as abstainers to report above-average health.

“Moderate Drinking May Boost Your Health,” by Krisha McCoy

Dr. Neil Binkley investigated the vitamin D status of people 93 people living in Hawaii.

Despite abundant sun exposure (a mean of approximately 11 hours per week of total body skin exposure with no sunscreen used), 51% of these individuals were found to have low vitamin D levels.

“This implies that the common clinical recommendation to allow sun exposure to the hands and face for 15 minutes may not ensure vitamin D sufficiency.”

“Adequate sun exposure no guard against low vitamin D,” by Will Boggs, MD

Men with higher levels of serum testosterone (T) have lower-status occupations, as indicated by archival data from 4,462 military veterans in six U.S. census occupational groups. Higher T, mediated through lower intellectual ability, higher antisocial behavior, and lower education, leads away from white-collar occupations. T levels are heritable and available early enough to affect a number of paths leading to occupational achievement. Prior research has related testosterone to aggression in animals and men, and high levels of testosterone presumably evolved in association with dominance in individual and small-group settings. Ironically, T, which evolved in support of a primitive kind of status, now conflicts with the achievement of occupational status.

T has been associated with dominance (Mazur 1985), aggression (Bernstein, Rose & Gordon 1974; Rose 1978), antisocial behavior (Dabbs & Morris 1990), sensation seeking (Daitzman & Zuckerman 1980), automaticity and perseverant responding (Broverman et al. 1964; van Hest, van Haaren & van de Poll 1989), libido (Morris et al. 1987; Sherwin, Gelfand & Brender 1985), and low verbal intelligence.

“Testosterone and Occupational Achievement” by James M. Dabbs Jr.