Genome Study Points to Adaptation in Early African-Americans

NY Times ^ | January 2, 2012 | NICHOLAS WADE

[neverdem]

Researchers scanning the genomes of African-Americans say they see evidence of natural selection as their ancestors adapted to the harsh conditions of their new environment in America.

The scientists, led by Li Jin of the Chinese Academy of Sciences in Shanghai, report in the journal Genome Research that certain disease-causing variant genes became more common in African-Americans after their ancestors reached American shores — perhaps because they conferred greater, offsetting benefits. Other gene variants have become less common, the researchers say, like the gene for sickle cell hemoglobin, which in its more common single-dose form protects against malaria. The Shanghai team suggests the gene has become less common in African-Americans because malaria is much less of a threat.

The purpose of studying African-American genomes is largely medical. Most searches for variant genes that cause disease take place in people of European ancestry, and physicians want to make sure they have not missed variants that may be more common in African-Americans and helpful for developing treatments or diagnosis.

Such searches often reveal events in a population’s history by pinpointing genes that have changed under the pressure of natural selection.

The unusually common variants identified by the Shanghai team are associated with higher risk of hypertension, prostate cancer, sclerosis and bladder cancer.

“Most of the genes associated with African-American ethnic diseases,” they write, “may have played an important role in African-Americans’ adaptation to local environment.” But the authors have not yet been able to identify the benefits they believe such genes conferred.

Mark D. Shriver, a geneticist at Penn State, said it was plausible that some versions of a gene would become more common as African-Americans adjusted to a new environment. “It’s very valid to expect that there will be factors subject to genetic adaptation and that are now more prevalent in...”

[Wonder Warthog]

"Oh yeah, because conditions on the veldt were so idyllic."

Conditions don't have to be "idyllic".....just different.

[RegulatorCountry]

Forced selection for the sickle cell trait is not natural. The premise is false, as is the conclusion.

[Wonder Warthog]

"Forced selection for the sickle cell trait is not natural. The premise is false, as is the conclusion."

ANY "selection pressure" is "forced" in some fashion or other. That "force" may be a mountain range, continental drift, a shifting river course, or human intervention. You seem to be hung up on the fact that these groups were made slaves and lost their freedom...which is totally irrelevant to the question of evolutionary change. The "selection pressure" on Ashkenazi Jews was also "human imposed", and thus, by your lights "not natural". Mother Nature doesn't care one way or another.

[El Gato]

The false premise here is that early African-Americans as a group were free to “select” and reproduce

I'm skeptical too, but the "selection" would occur as people died before being able to reproduce, whether they chose who they reproduced with or not. Of course lots of European genes were introduced by slaveholders and their overseers.

[RegulatorCountry]

Of course lots of European genes were introduced by slaveholders and their overseers.

Overseers, yes. Widespread antipathy still toward Scotch-Irish, who comprised the majority of overseers. Owners? Not so much as pop culture and politically motivated historical revisionism would lead one to believe. It happened but was not all that common.

Scan back upthread for the link provided by AdmSmith, which provides the most common means of introduction.