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Tracing ancient genes

Prehistoric Europe was home to hunter-gatherers until migrating farmers muscled them out. Genetic information teased from ancient skeletons is helping scientists reconstruct this saga, as Tina Hesman Saey reported in “Written in bone” (SN: 5/17/14, p. 26).

Sometimes, untangling genetic history can be a little one-sided. Researchers often rely on mitochondrial DNA, passed on only from the mother. As Debra Baker noted, this presents a problem: “Couldn’t the lack of similarity of mitochondrial DNA among the different groups arise because they all were matrilineal?” she asked in an e-mail. “Instead of group isolation as suggested by the article, there could have been interbreeding, but the child would have remained in the mother’s group.”

It’s entirely possible that social structures could influence the results when looking at genetic data from just one parent, says Saey. “That’s why scientists prefer to study the whole genome, or nuclear DNA, when they can. Ancestral contributions from both parents are apparent when you look at the entire genetic picture, as some of the studies mentioned in the story have. Nuclear DNA has been hard to get, but increasingly scientists are extracting more and better DNA out of ancient fossils. Expect to see more in-depth examinations of prehistoric people and their relationships in the future.”

Antimicrobial advice

In “Triclosan aids nasal invasions by staph” (SN: 5/17/14, p. 12), Beth Mole reported that a common antimicrobial component of hand soaps boosts the stickiness of a disease-causing bacterium, allowing it to better cling to human proteins.

The troubling finding calls for more research, wrote John Turner. “Now that we’ve learned that low-level triclosan exposure can actually enhance the adhesion and competitiveness of staph bacteria on surfaces in the body, isn’t it time we checked what it’s doing in, say, our toothbrushes? Often formulated of triclosan-containing plastics and smeared with triclosan-containing toothpaste?”

Until scientists gather more data, practical advice on hand-washing is in order: “Soap and hot water, folks. You don’t need all that fancy stuff that only builds up resistance, and apparently, infectious snot,” wrote reader Jan Steinman. “In a pinch, a bit of vinegar works wonders, too.”

Musings on mammal milk

Naked mole-rat milk contains more water than other rodents’, possibly to keep the young hydrated in arid habitats. Susan Milius touched on the variety of mammal milk in “How to milk a naked mole-rat” (SN: 5/17/14, p. 4).

Milk proved to be a hot topic for discussion among readers. “I would think the aquatic species’ fat content may have to do with needing the high calories for warmth, and increasing fat layers in young to maintain that warmth,” wrote Anthony Kerwin. “It would be interesting to see how the relationship would bear out for just terrestrial mammals, or even among similar species in different climates.”

Biologist Wendy Hood of Auburn University in Alabama replies: “Marine mammals need to fatten quickly to survive in an aquatic habitat. In fact, the hooded seal has to be ready to forage for itself in the cold arctic waters after just four days of suckling. In that period of time, the pup doubles in mass — that change is mostly due to deposition of fat.” She adds, “Smaller species require more energy relative to their size than a larger species, so higher milk fat — in the case of a mouse — gives the pups more energy to support the energy demands of growth. It’s interesting that naked mole-rats are so different, but the lower-fat milk is in part explained by the lower energy requirements of naked mole-rats relative to other rodents.”

Correction

The web link provided in “Outgoing Congressman Rush Holt calls scientists to action” (SN: 6/14/14, p. 4) contains an error. The correct link is: bit.ly/SN_holt