Senin, 26 Juli 2010

Familial DNA Searches

DNA testing is a modern way to positively match DNA left at a crime scene to a suspect. But what if police have DNA from a crime scene but no suspect? Most states have DNA banks only of convicted felons already in prison, so a criminal with no prior record would almost certainly go undetected.

One method being used in California is to look for partial matches between DNA from a crime scene and the state’s database of DNA from convicted criminals. A partial match, while not implicating the criminal himself, would suggest that a close relative might have carried out the crime. California used the method this month to identify a person previously convicted on a weapons charge as “probably related” to a long-sought-after Los Angeles serial killer known as the Grim Sleeper. The person’s father eventually was arrested and charged with ten murders.

This is new ethical ground for us all. As a society we need to understand the costs vs. benefits of these types of searches. The benefits are obvious – another killer identified. But the costs will be freedom lost – the freedom, for example, not to be put under suspicion and investigated for a crime unless there is reason to suspect you of an offense. Suspicion of relatives based on partial DNA matches is likely to fall disproportionately on African Americans, since they already represent a disproportionate fraction of the prison population.

Because of these concerns, California wisely put some safeguards in place for familial DNA searches. Currently, such searches require that all other investigative leads have been exhausted, that the crime is murder or rape, and that the criminal is still committing crimes – i.e. is still a threat to society. Other states considering familial DNA searches should consider similar safeguards.

Jumat, 23 Juli 2010

Cotton Pests Infest GM Cotton

It was bound to happen, given enough time. In western India, a species of cotton bollworm has now developed the ability to infest genetically modified (GM) cotton that was specifically engineered to resist bollworm infestation.

GM cotton has become increasingly popular with farmers – so popular that approximately 50% of all cotton planted worldwide is now GM cotton. The largest users (and cotton growers) are China, India, and the United States, in that order. With so much GM cotton being planted, we could have anticipated that the cotton pests would adapt eventually. But it’s surprising how quickly it happened – bollworm-resistant cotton was only first planted in India in 2002.

Realistically, we can expect the current generation of GM crops to remain useful for several more decades. In the meantime I’m sure that researchers at Monsanto will be working on new ways to thwart the pests, just as the pests will be slowly adapting. It’s just part of the ongoing battle between species for survival.

Rabu, 21 Juli 2010

A New (Extinct) Human Ancestor

Scientists have discovered two partial skeletons of a new species of the genus Australopithecus near Johannesburg, South Africa, which they named Australopithecus sediba. The new australopithecines, nearly 1.95 million years old, appear to be closely related to both A. Afarensis and A. africanus.

Of course, paleoanthropologists are already debating where to place A. sediba in the human family tree; direct human ancestor, or evolutionary dead end? Regardless of the outcome, the new find is significant in that it fills some gaps in our understanding of evolutionary processes leading to humans. For instance, it appears that changes in the shape of the pelvis occurred before brain enlargement, and that the legs underwent adaptive changes for upright walking before the arms took on smaller, more human-like proportions.

Minggu, 18 Juli 2010

Using Bacteria to Fight Bacteria

A recent article in the New York Times is a good primer on the astonishing variety of bacteria that colonize our bodies, and what they may be doing there. It turns out that our individual microbiomes (all of the microbes in a defined environment within our bodies) are quite different. And at any one time, each of us probably has only about 20% of the species of bacteria that can inhabit the human body.

An interesting new idea is that the “good” bacteria in certain people’s microbiomes might actually be used to treat certain diseases. Doctors have actually cured several stubborn cases of severe diarrhea caused by a particularly difficult bacterium to treat (Clostridium difficile) by transplanting human fecal matter from a healthy person into the patients’ colons! Granted, having a fecal transplant in order to cure disease sounds a bit strange. But apparently the “good” bacteria in the fecal transplant outcompete the C. difficile and wipe them out.

Someday maybe there’ll be ointments or pills containing especially “good” bacteria for treating certain antibiotic-resistant infections such as flesh-eating Staphylococcus aureus or diarrhea-causing C. difficile. Using bacteria to kill bacteria – like using fire to fight fire.

Reference: Zimmer, C., How Microbes Defend and Define Us. New York Times, July 13, 2010.

Selasa, 13 Juli 2010

Heritable, Non-Genetic Behavioral Patterns

Why do abused children grow up to be abusive parents? Why do people raised in lower socio-economic environments tend to have more long-term health problems? Why is it so hard for drug addicts to kick their habit?

For possible answers, behavioral neuroscientists are turning to a hot new field called behavioral epigenetics. Behavioral epigenetics is the study of inherited changes in behavior or gene expression that are caused by factors other than changes in DNA, i.e., that are epi- (Greek: over, above) genetics.

According to epigenetics theory, environmental factors such as the degree of nurturing (or lack of it) by one’s parents early in life can alter the chemical structure of DNA (specifically, the degree of methylation of DNA and its associated histones). This in turn affects how and when certain genes are turned on and off. In theory, such chemical alterations in DNA could last for multiple generations (i.e., be heritable) even though the nucleotide sequence of the genes themselves hasn’t changed.

So far, there’s very little evidence to suggest that epigenetic mechanisms influence human behavior, mostly because human brain tissue is not readily available for research. However, laboratory studies show that rats raised by less-nurturing mothers tend to be more prone to stress as adults and to exhibit increased methylation of certain genes. It’s worth keeping an eye on this developing field to see where it leads.

Rabu, 07 Juli 2010

It's Official: She Can Compete

It took more than 10 months for a committee of the IAAF, international track and field’s governing body, to decide that Caster Semenya could compete in track and field events as a woman. As you may recall, Ms. Semenya’s gender was called into question after she completely dominated the 800-meter event in the world championships last August in Berlin (see this blog, Sept. 7, 2009.) A statement released yesterday by the IAFF on their Web site ( reads in full:

Caster Semenya May Compete. “The process initiated in 2009 in the case of Caster Semenya (RSA) has been completed. The IAFF accepts the panel of medical experts that she can compete with immediate effect. Please note that the medical details of the case remain confidential and the IAAF will make no further comment on the matter.” (IAFF statement)

Remember the old “Where’s the beef?” commercials for Wendy’s chain of restaurants? One might ask, “Where’s the proof?” Out of fairness to all athletes in sports, sports governing bodies should develop understandable policies, guidelines, or criteria for gender assignment in sports. But it won’t be easy (gender IS ambiguous, sometimes), so I’m betting the IAAF won’t even attempt it.

The Wendy’s commercial ended with the remark, “(I don’t think there’s anybody back there…)” IAAF, are you listening?

Jumat, 02 Juli 2010

Studying Human Behavior

What drives human behavior? In a provocative paper published online in Behavioral and Brain Sciences last week, it is argued that much of what we believe we know about human behavior is skewed by the fact that most psychological studies are performed on WIERDs – subjects from Western, Educated, Industrialized, Rich, Democratic societies. Indeed, most human subjects used in psychological studies are from the United States, according to an article published several years ago in American Psychologist by Jeffrey Arnett. And most of the subjects are psychology undergraduate students – hardly representative of the world’s cultures as a whole.

How might this affect the results? Take for example, perception of self. Textbooks generally describe people has having a tendency to rate their own abilities as above average and to be motivated to maintain a positive image of themselves. But this may not necessarily be true for non-WEIRD cultures, who may place more emphasis on family relationships and less on personal choice or ability.

There’s nothing inherently wrong with studying WEIRDs, of course, as long as it is understood that the conclusions may not generalize to all cultures.

Reference: Henrich, Joseph et al. The Weirdest People in the World? Behavioral and Brain Sciences 33 pp. 61-83.

Lucy's Older Brother

Remember “Lucy”, the first nearly complete skeleton of Australopithecus afarensis, an extinct species of early human ancestor? Well, now partial remains of her older “big brother” have been found, though technically he’s not her brother because he lived nearly half a million years earlier. But at 5 – 5 ½ feet tall he is big by early human ancestor standards. Kadanuumuu, or “big man”, as he was nicknamed, had a rib cage and shoulder blade (scapula) more like a modern human than a chimpanzee. In addition, his legs were long compared to his arms, another feature that is more humanlike than apelike.

This second Australopithecus afarensis partial skeleton strengthens the hypothesis that although early human ancestors were not entirely humanlike, they also did not resemble modern apes or chimpanzees.

Details were published online on June 21 in the Proceedings of the National Academy of Science, ahead of the print version.

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