Why do only *some* adults drink milk?

Over at Seedmagazine.com, my new column "Research Blogging" debuted today. Every Wednesday I'll be discussing what's new in the research blogosphere, and this week I cover a fascinating post by Jeremy Yoder about lactose tolerance in adults. Here's a sample:

The researchers say the lactase gene evolved in Europe because Europeans don't get enough sun to produce Vitamin D, which in turn is needed for humans to take in calcium. Since lactose also assists in the uptake of calcium, adult milk drinking helped northern Europeans meet that deficiency.

Gerbault's team developed a computer model demonstrating that, in order for the adaptation to persist, lactose-tolerant northern Europeans would need to have 1.8 percent more children. In other words, milk drinkers would need to be more successful in reproducing--and this is indeed what is observed there.

Read the whole thing here.

Also, in case you missed it, yesterday on ResearchBlogging.org, I highlighted some of the best psychology and neuroscience posts of the past week:

More like this

For an oh-so-subtle reason, the "attractiveness ratings" link is broken. The reason is easy to miss, but it's because the URL uses a real apostrophe (â) where the link uses a single quote mark (').

On the lactose tolerance article, I must be critical of one part of it - namely that in saying "lactase persistence evolved separately in northern Europeans and Africans", you neglect to indicate (even in vague terms) which African populations you're talking about.

All the research mentioned in your Seed column is fascinating, to be sure. But "groundbreaking"? I don't think so.

I wrote Milk Is Not for Every Body: Living with Lactose Intolerance in 1996. For that book I scoured the literature, both medical and anthropological, for the origins of lactose tolerance. Every piece of "news" in your column was covered in my book, from the need for more vitamin D to the usefulness of lactose tolerance in absorbing calcium to the slight increase in reproductive ability to the origins of lactation.

DNA research is a marvel and I expect deep, meaningful, and live-changing results to appear almost daily. But the researchers of the past, who necessarily had to use cruder methods but with equal or greater deductive ability, need to be referenced and honored for their pioneering work, work that the DNA researchers are merely confirming.

Re: "The African populations came from across the continent."

The Wikipedia article on lactose intolerance says that most sub-Saharan Africans are not lactose tolerant. Granted, Wikipedia is not the final authority, but the reason I looked it up in the first place is that I found your article implausible on this point. Given the genetic diversity of humans in Africa, a genetic change affecting "Africans" in general (but not humans elsewhere) would have to evolve independently in the various African populations, yet the article acknowledges no such thing. What am I missing?

I'm not calling for detailed information here, but I think that referring to generic "Africans" is just too vague. Phrases such as "some/many/certain African populations", only marginally more precise, would not have attracted my criticism.

(P.S. Are you sure you fixed the link? Looks unchanged from here.)

Dave: no you haven't. Link still broken for me. Here is a fixed one: here

By Philip Potter (not verified) on 12 Aug 2009 #permalink

"Women eat less than dining with men" - perhaps that should read "some young university women eat less when on social occasions with potential mates."

Older, married women will tell you about the phenomenon of "husband weight." When women are married, they tend to gain weight because they eat the same meals that their husbands eat, which are normally larger and more fattening than the meals they eat when they are with other women.

I apologize for the problem with the link to the "hot or not" post. It's now really, truly fixed (this blogging platform doesn't play nicely with curled apostrophes).

Regarding the question of distribution of lactose tolerance in Africa, it is possible for a trait to be evenly distributed without being present in all members of a population. I believe my summary is accurate. For more details, please read the original research report.

Re lactose tolerance: I found it intriguing that in most mammals lactose tolerance disappears after weaning. I and several people I know have become lactose intolerant as adults, after having no difficulty with milk products earlier in life. Wonder if it could be a similar mechanism at work, just later. Does need for vitamin D dissipate after fertile years?