Saturday, November 24, 2012

Why did homosexuality evolve?

Really interesting article from the Chronicle about why homosexuality may have evolved, despite being such a seeming weakness from an evolutionary perspective.  

The short answer is that we don't know, but several good theories are presented.  My two favorites are the "sexually antagonistic selection" theory and the "nonadaptive byproduct" theory.  

Here's the sexually antagonistic selection theory: 
What if one or more genes that predispose toward homosexuality (and with it, reduced reproductive output) in one sex actually work in the opposite manner in the other sex? I prefer the phrase "sexuallycomplementary selection": A fitness detriment when genes exist in one sex—say, gay males—could be more than compensated for by a fitness enhancement when they exist in another sex.
Anyone prefer any of the other theories?  I'm skeptical of the group selection and social prestige theories.  It seems like there would have to be a pretty enormous benefit conferred upon one's relatives to offset not having children of one's own.  

Breast cancer screenings

The Lancet reports on the findings of the independent UK Panel on Breast Cancer Screening:
The Panel found that routine breast screening leads to a 20% relative risk reduction compared with no screening. This means for every 235 women invited for screening, one breast cancer death will be prevented, representing 43 breast cancer deaths prevented per 10 000 women aged 50 years invited to screening for the next 20 years.
Additionally, the Panel found that some overdiagnosis occurs. 19% of breast cancers diagnosed in women invited for screening would not have caused any problem if left undiagnosed and untreated (a rate of 129 per 10 000 women). However, owing to the scarcity of reliable data in this area, more research is needed to accurately assess the magnitude of overdiagnosis. The Panel also considered how women feel about the available evidence: many women believe the balance of benefits to risks is worthwhile.
I'm not sure that this is conclusive, as the article's title suggests, but it seems like a strong evidence point in favor of continuing screenings in women 50 and above.