Progress Daily

Viewing curvaceous women has an effect on straight men’s brains similar to that of alcohol and other drugs.

Steven Platek’s researchers asked 14 men (average age of 25) to rate women’s attractiveness before and after plastic surgery that moved fat from their waist to buttocks, changing their waist-to-hip-ratio (WHR).

FMRI showed activation in the subjects’ brain reward centers in response to naked female bodies when surgically altered to express an optimal (~0.7) WHR with redistributed body fat, but relatively little activation when body mass index (BMI) was altered.

“Optimal Waist-to-Hip Ratios in Women Activate Neural Reward Centers in Men”

“Watching curvaceous women feels like drugs to men: study, goodnews

The evidence suggests that as the number of cyclists in a city increases, the level of safety-per-cyclist increases so quickly that more bike riders leads to fewer bike accidents.

“Safety in Numbers: It’s Happening in NYC,” by Ben Fried

“Safety in Numbers,” by Matthew Yglesias

A study by Amir Barnea, Henrik Cronqvist and Stephan Siegel (”Nature or Nurture: What Determines Investor Behavior?“), based on characteristics for approximately 40,000 identical and non-identical twins from the Swedish Twin Registry and associated investing data for the period 1998-2006, concludes that genetics explain up to 45% of individual variation in stock market participation, asset allocation and portfolio risk choices.

Genetic influence is robust to differences in age, education and net worth. Genetics explain more of the variation in individual investing behavior than does an extensive set of individual characteristics combined.

Family environment has an effect on the investing behavior of younger individuals, but this effect disappears as they acquire non-family experiences.

“The Genetics of Investing (Not the Algorithms),” CXO

In a study just published in Evolution and Human Behavior (”Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity“), Steven Gaulin analyzes muscularity.

The data came from the NHNES, which followed 12,000 American men and women over the course of 6 years. The researchers found that men require 50% more calories than women do, even after adjusting for activity levels, and that their muscle mass is the strongest predictor of their intake of calories — stronger than their occupation or their body-mass index. Men’s immune systems are less effective than those of women (which was known before), and become worse the more muscular the men are (which was not).

The more muscular a man, the more sexual partners he reported, both in the past year and over his lifetime, and the earlier his first sexual experience was likely to have been.

Gaulin speculates that an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.

“Mr Muscle,” The Economist

Research by Paola Sapienza & Luigi Zingales (”Gender differences in financial risk aversion and career choices are affected by testosterone“) suggests that testosterone levels may explain why men dominate risky financial professions.

The researchers measured the amount of testosterone in the saliva of aspiring bankers (MBA students from the University of Chicago). They also estimated the students’ exposure to the hormone before they were born by measuring the ratios of their index fingers to their ring fingers (a long ring finger indicates high testosterone exposure) and by measuring how accurately they could determine human emotions by observing only people’s eyes, which also correlates with prenatal exposure to testosterone.

The students had to decide between a 50:50 chance of getting $200 or a gradually increasing sure payout, which ranged from $50 up to $120. The point at which a participant decided to switch from the gamble to the sure thing was reckoned a reasonable approximation of his appetite for risk.

Women and men with the same levels of testosterone generally switched at the same time, demonstrating similar risk preferences. Women who had more testosterone were more risk-loving than women with less, while the data for men at the lower end of the spectrum displayed a similar relationship. Curiously, the relationship between testosterone and risk taking was not as strong for men with moderate to high levels.

The correlation was strongest when the salivary measure of testosterone was used.

The researchers then followed the subjects’ progress after they graduated, to see what sort of careers they entered. Men were more likely than women to choose a risky job in finance but the difference was accounted for entirely by their levels of salivary testosterone.

“Risky business, The Economist

Toxoplasma gondii is a parasite that lives in the guts of cats, where it sheds eggs in cat feces that are often eaten by rats. The parasites increase their odds of getting back to cats by changing the infected rats’ brains, making them less scared of cats (and so more likely to be eaten).

A new study by Jaroslav Flegr, Jan Havlíček, et. al, (”Increased incidence of traffic accidents in Toxoplasma-infected military drivers and protective effect RhD molecule revealed by a large-scale prospective cohort study“) found that subjects with high titers of anti-Toxoplasma antibodies had a probability of a traffic accident (17%) more than 6 times higher than Toxoplasma-free subjects.

“The Return of the Puppet Masters,” by Alex Tabarrok

Stephen Garcia & Avishalom Tor analyzed the results of the the Cognitive Reflection Test & the 2005 SAT exam. They calculated the average number of test-takers per venue in each state, and found that test scores fell as the number of people in the examination hall increased.

They then asked 74 university students to take a timed, easy general-knowledge quiz. Each student completed the test alone, but half were told they were competing against ten other people and the other half that they were competing against 100. All were informed that those whose completion times were in the top 20% would receive $5. Students who believed they were competing against only ten people finished in an average of 29 seconds. Those who believed they were competing against 100 averaged 33 seconds.

They then ran a 2nd experiment, & asked students to imagine they were running a five-kilometre race against 50 people and then against 500 (or, in half of the cases, the other way round). In both notional races the top 10% of competitors would get a $1,000 prize. The researchers told the students to rate, on a seven-point scale, how much faster than normal they would run in each notional race, with a one being slightly faster than normal and a seven being the fastest of their lives. The average value in the competition against 50 others was 5.4; in the competition against 500 it was 4.9. They then asked the participants a series of questions commonly used by psychologists to evaluate an individual’s tendency to compare himself with others in a social environment. They found that those with the highest tendency to make such comparisons had the lowest scores in the notional race against 500 others.

“The N-Effect: More Competitors, Less Competition”

“Psyched out,” The Economist

Two years ago, a study by Carsten Wrosch (”You’ve Gotta Know When to Fold ‘Em: Goal Disengagement and Systemic Inflammation in Adolescence“) demonstrated the importance of giving up inappropriate goals — those teenagers who were better at doing so had a lower concentration of C-reactive protein, a substance (made in response to inflammation and) associated with an elevated risk of diabetes and cardiovascular disease.

A recent study by Dr Wrosch and Gregory Miller (”Depressive symptoms can be useful: Self-regulatory and emotional benefits of dysphoric mood in adolescence“) measured the “goal adjustment capacities” of 97 girls aged 15-19 over the course of 19 months. They asked the participants questions about their ability to disengage from unattainable goals and to re-engage with new goals.They also asked about a range of symptoms associated with depression, and tracked how these changed over the course of the study.

Those who experienced mild depressive symptoms could disengage more easily from unreachable goals. They also proved less likely to suffer more serious depression in the long run.

The prevalence of inappropriately optimistic persistence may help explain why the US has the highest depression rate in the world.

“Mild and bitter,” The Economist

A series of a series of experiments (”Positive Self-Statements: Power for Some, Peril for Others“) by Joanne Wood suggest that positive self-statements cause negative moods in people with low self-esteem. The researchers questioned a group of 68 men and women using long-accepted methods to measure self-esteem. The participants were then asked to write down their thoughts & feelings. In the midst of this, half were randomly assigned to say to themselves “I am a lovable person” every time they heard a bell ring.

Immediately after the exercise, they were asked questions such as “What is the probability that a 30-year-old will be involved in a happy, loving romance?” to measure individual moods using a scoring system that ranged from a low of zero to a high of 35.

Those with high self-esteem who repeated “I’m a lovable person” scored an average of 31 on their mood assessment compared with an average of 25 by those who did not repeat the phrase. Among participants with low self-esteem, those making the statement scored an average of 10 while those that did not managed an average of 17.

“Words of wisdom,” The Economist

Non-kin altruism among non-human animals is rare, & altruism fares poorly in computer simulations — when altruistic individuals emerge in a community characterized by self-interested behavior, selfishness triumphs.

Group selection could explain the prevalence of human altruism but probably only if the ancestral environment included high levels of violence and inbreeding.

Sam Bowles showed in 2006 that genetic analyses of tribes still living a Stone Age life suggests there was enough inbreeding to make group competition a driver of genetic change.

In ancient graves excavated previously, Bowles found that up to 46% of the skeletons from 15 different locations around the world showed signs of a violent death. More recently, war inflicted 30% of deaths among the Ache, 17% among the Hiwi, & just 4% among the Anbara. Combat between groups accounted for about 14% of all deaths in these hunter-gatherer societies.

After estimating the rate that altruism would reduce an individual’s chances of reproducing, Bowles plugged the numbers into a model of intergroup competition where an individual’s altruism would also improve a group’s chances of combat triumph. In the absence of war, a gene imposing a self-sacrificial cost of as little as 3% in forgone reproduction would drop from 90% to 10% of the population in 150 generations. Bowles predicts that much higher levels of self-sacrifice — up to 13% in one case — could be sustained if warfare were brought into the equation.

“Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” By Samuel Bowles

“Altruism’s Bloody Roots,” by Brandon Keim

“Ancient warfare: Fighting for the greater good,” by Ewen Callaway

“Blood and treasure,” The Economist