How, he wondered, could you have the same odor in two different populations on two different continents?
He set up his own body-odor experiment with colleagues at Penn, Monell, and the Karolinska Institute in Sweden. The results were published in Friday's issue of the journal Public Library of Science One.
He recruited three groups of "donors" and 41 volunteers willing to sniff their odors. The donors came from three discreet age groups: young (20 to 30), middle aged (45 to 55), and old (75 to 95).
To keep the sniffers blind to the participants' ages, he collected the odors using t-shirts with special pads sown into the armpits. He asked the donors to wear the shirts to bed after showering and washing with a non-perfumed soap. They slept in the shirts for five nights in a row.
The sniffers had to figure out which odors were similar to each other. This they did quite well, said Lundstrom. They did a particularly good job of grouping all the odors from the old people. They were slightly less adept at distinguishing middle-aged b.o. from youthful b.o.
A second task showed humans are not so good at using smell to judge age. The sniffers performed better than chance when identifying odor pads that came from the 75-to-95 age category, said Lundstrom, but not much better. They couldn't tell which age groups produced the other two sets of odor pads.
It's possible, Lundstrom said, that the sniffers were detecting the smell of inflammation and creeping illness. If that's the case, at least the smells weren't rated as unpleasant. In men it was quite the opposite, said Lundstrom. "Young guys are stinky, middle aged guys are even more stinky, and when they got old it goes away."
The concentration of odor-producing chemicals declines back to prepubescent levels as men get old. "They return to childhood levels by age 80" - a sort of second childhood of body odor, he said.
Contact Faye Flam at 215-854-4977, email@example.com, on her blog at www.philly.com/evolution, or @fayeflam on Twitter.