Sunday, November 19, 2006

Speeded up evolution can be predicted

Pressured by predators, lizards see rapid shift in natural selection

November 17, 2006 - CAMBRIDGE, Mass. -

Countering the widespread view of evolution as a process played out over the course of eons, evolutionary biologists have shown that natural selection can turn on a dime - within months- as a population's needs change. In a study of island lizards exposed to a new predator, the scientists found that natural selection dramatically changed direction over a very short time, within a single generation, favoring first longer and then shorter hind legs. The findings, by Jonathan B. Losos of Harvard University and colleagues, are detailed this week in the journal Science.Losos did much of the work before joining Harvard earlier this year from WashingtonUniversity in St. Louis.

"Because of its epochal scope, evolutionary biology is often caricatured as incompatible with controlled experimentation," says Losos, professor of organismic and evolutionary biology in Harvard's Faculty of Arts and Sciencesand curator in herpetology at the Harvard Museum of Comparative Zoology. "Recentwork has shown, however, that evolutionary biology can be studied on short time scales and that predictions about it can be tested experimentally. We predicted,and then demonstrated, a reversal in the direction of natural selection acting on limb length in a population of lizards."

Losos and colleagues studied populations of the lizard Anolis sagrei onminuscule islands, or cays, in the Bahamas. They introduced to six of these caysa larger, predatory lizard (Leiocephalus carinatus) commonly found on nearby islands and known as a natural colonizer of small cays. The scientists kept sixother control cays predator-free and exhaustively counted, marked, and measured lizards on all 12 isles.

Anolis sagrei spends much of its time on the ground, but previous research has shown that when a terrestrial predator is introduced, these lizards take totrees and shrubs, becoming increasingly arboreal over time. Losos and hiscolleagues hypothesized that immediately following a predator's arrival,longer-legged - and hence faster-running - Anolis lizards would be favored to elude capture. However, as the lizards grew ever more arboreal in habitat, the scientists projected that natural selection would begin to favor shorter limbs, which are better suited to navigating narrow branches and twigs.

Their hypothesis was borne out. Six months after the introduction of the predator, Losos found that the Anolis population had dropped by half or more on the islands with the predators, and in comparison to the lizards on the predator-free islands, long legs were more strongly favored: Survivors had longer legs relative to non-survivors. After another six months, during which time the Anolis lizards grew increasingly arboreal, selective pressures were exactly the opposite: Survivors were now characterized by having shorter legs on the experimental islands as compared to the control islands.

The behavioral shift from the ground to higher perches apparently caused this remarkable reversal, Losos says, adding that behavioral flexibility may often drive extremely rapid shifts in evolution.

“Evolutionary biology is by its nature an historical science, but the combination of microevolutionary experimentation and macroevolutionary historical analysis can provide a rich understanding about the genesis of biological diversity,” the researchers write.

Friday, November 03, 2006

"My genes made me do it"


Psychiatric News November 3, 2006Volume 41, Number 21, page 12© 2006 American Psychiatric Association

Jury Still Out on Impact Of Genes on Trial Verdicts

Mark Moran

Americans should not be surprised to hear that claim made by criminal defendants as the genetics of behavior, especially antisocial behavior, are explored by science and popularized.

Paul Appelbaum, M.D., chair of APA's Council on Psychiatry and Law, told psychiatrists at APA's 58th Institute on Psychiatric Services last month that the findings of behavioral genetics—even such preliminary findings as have been made to date— are making their way into the American legal system.

He predicted, however, that genetic arguments are not likely to be successful in freeing defendants from guilt for their crimes, but may more likely be advanced in criminal cases as mitigating factors that should be taken into account in sentencing. Yet even there it remains to be seen how a genetic propensity will be viewed by juries and judges; such evidence could just as conceivably be seized upon as an argument against a defendant, Appelbaum said.

"If effective treatment becomes available, the pressure to identify [at-risk individuals] through screening at birth may be irresistible."

Still, the groundwork for the logic of a genetic defense, in the form of the insanity defense, has already been laid by centuries of case law.

"Anglo-American law has created categories to excuse defendants from culpability when their capacity to choose their behavior is significantly impaired," Appelbaum said. "If mental disorders that impair appreciation of wrongfulness or ability to control behavior negate culpability, why shouldn't genetic determinants have the same effect?

"Why should there not be a defense of genetic determinism, a `my genes made me do it' defense? The logic [of moving] from the existing insanity defense to such an argument is not so absurd that it has not already begun to make an appearance in our courts."

Linking MAOA and Violence

Already rippling through the legal system with intriguing implications is a landmark study by Avshalom Caspi, Ph.D., and colleagues that appeared in Science in 2002 demonstrating a remarkable interaction between a specific genetic configuration and early childhood experiences in the development of antisocial disorder.

Drawing on a sample of more than 400 males in Dunedin, Scotland, who had been followed since childhood for 26 years, Caspi and colleagues were able to examine the levels of monoamine oxidase A (MAOA) activity in those who did and did not exhibit antisocial behavior, including violence, in later years.

MAOA is an enzyme that sits on mitochondrial membranes in neurons and degrades several important neurotransmitters, including several believed to be important in the regulation of aggression and impulsivity. Previous animal research had shown that the absence of MAOA was associated with increased aggression. Levels of MAOA activity differ based on variation in the "promoter region" of the MAOA gene, which controls the transcription of the DNA into messenger RNA.

Caspi and colleagues found from their longitudinal work with the Dunedin sample that low MAOA activity was not itself predictive, but that low MAOA activity in combination with a history of child abuse or neglect was predictive of antisocial behavior, including violence. Individuals with low MAOA activity and severe maltreatment comprised just 12 percent of the sample, but they accounted for 44 percent of the violent crimes committed by the sample. . . .

Are you out of shape?

AGGRESSIVE TENDENCIES MAY BE REVEALED BY ASYMMETRY IN BODY PARTS, STUDY FINDS

COLUMBUS, Ohio – Researchers may get some indication of how aggressively an angry person will react by measuring the size relationship between a person’s ears and other body parts, according to a new study.

Research showed that the farther certain paired body parts were from symmetry – if one ear, index finger or foot was bigger than another, for example – the more likely it is was that a person would show signs of aggression when provoked. The symmetry effects were different in men and women, however.

While the findings may seem strange, there is a plausible explanation, said Zeynep Benderlioglu, co-author of the study and a post-doctoral researcher at Ohio State University.

Deviations from symmetry are thought to reflect stressors during pregnancy – such as poor health, alcohol and tobacco use – that may affect development of the fetus in a variety of ways.

"Paired body parts are presumably controlled by similar genetic instructions, so if everything goes perfectly you would expect paired body parts to be the same size," Benderlioglu said.

"But stressors during pregnancy may lead to asymmetrical body parts. The same stressors will also affect development of the central nervous system, which involves impulse control and aggression," she said. "So while asymmetry doesn’t cause aggression, they both seem to be correlated to similar factors during pregnancy."

Benderlioglu conducted the study with Randy Nelson, a professor of psychology and neuroscience, and Paul Sciulli, professor of anthropology, both at Ohio State. Their results were published in a recent issue of the American Journal of Human Biology....

Benderlioglu said the same conditions in pregnancy that lead to asymmetry in body parts probably affects development of parts of the central nervous system that deal with impulse control. The result is that people with higher levels of asymmetry also have a harder time controlling their aggressive impulses.

Other studies have indicated that testosterone is related to a tendency toward anger. So people who show both high levels of asymmetry and high levels of testosterone may react particularly aggressively when provoked, she said....

The results emphasize once again the importance of healthy habits during pregnancy, Benderlioglu said. Smoking and heavy alcohol use are among the stressors that may lead to both asymmetry and poor impulse control....

Thursday, November 02, 2006

Guns, Genes, and Steel

Whistling Past the Graveyard
by John Derbyshire (Nov. 2006)
Reviewing Mark Steyn's new book, America Alone
. . . .

Ah, culture. Of course it’s not about race! Nothing is about race, because there is no such thing as race. (Repeat 100 times.) It’s about culture—the aether, the phlogiston, of current social-anthropological speculation, whose actual nature is mysterious, but whose explanatory power is infinite. You know, culture: those habits, folkways, beliefs, ways of thinking and behaving and connecting that arise from... pure chance! Or geography (see below). Or something... but definitely nothing to do with biology.

Please don’t get me wrong. I am sure Mark Steyn is sincere here. I am sure he believes this stuff about “culture.” Most educated people do. Most will continue to do so for a few more years, while the neuroscientists, geneticists, genomicists, anthropologists, paleontologists, and statistical sociologists sap away beneath them—until the ground gives way. (A professional academic biologist friend of mine is in the habit of snapping out, any time anyone takes refuge in this “culture” stuff: “Culture? Culture? What does that mean? Where does it come from? What are the upstream variables?”)

One of the great anthropological-historical best-sellers of recent years was Jared Diamond’s Pulitzer-prize-winning Guns, Germs, and Steel. Different human populations, in different parts of the world, says Diamond, developed different cultures, depending on whether they had draft animals to hand, easy routes for disease transmission, and so on. Diamond almost completely ignores the role of inheritance and natural selection in shaping human populations. Natural selection? That all came to a screeching halt 50,000 years ago, don’t you know, when homo sapiens showed up. There have been no biological changes since then, none at all! Certainly none that affect behavior or socialization. We are all exactly the same structurally, we just behave differently according to the local geography. Location, location, location.

Alas, our understanding of population genetics has already left Jared Diamond behind. Good, solid scientific studies are beginning to appear that altogether refute the “culture” paradigm. We are not a uniform species, inclined to different folkways by the pressures of geography. A population of human beings, breeding mostly within itself, is shaped by the menu of genetic peculiarities it started out with, and by its breeding practices (did you know that 55 percent of Saudi marriages are between first or second cousins?), and by its environment. We are not a uniform species at all. Not many world-wide species are.