Letters

Early puberty’s cause
Regarding “Early Arrival” (SN: 12/1/12, p. 26): In 1960 I left the Ohio Valley of grass- and corn-fed cows to teach in the Los Angeles area. When I arrived, I found that eighth- and ninth-grade girls looked physically like 25-year-old women in Ohio. I asked the other teachers what was going on. They all responded, “beef growth hormones.” If researchers would track earlier puberty in preteen girls alongside the use of growth hormones in cattle, they would most likely find matching graphs. Is this another horror of fast food such as hormone-laden hamburgers?
Irene Baron, Zanesville, Ohio

Meat and dairy products from animals given growth-promoting hormones has long been a concern among parents and physicians, but the relationship can be difficult to study (for example, children who consume a lot of meat and dairy may also be overweight). One of the more recent studies, which followed 7,500 children in Hong Kong, was published in the Sept. 1 Pediatrics. It did not find that the onset of puberty was associated with the consumption of cow’s milk. —Laura Beil

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Symbolic illogic
As soon as I saw the ® in the editor’s letter (SN: 12/15/12, p. 2), I thought of the Pioneer message plaque designed by Carl Sagan. The first time I saw that placard and the discussion of the message it purportedly contained, I questioned the symbolism. An arrow is an anthropomorphic symbol that could only be understood by one familiar with the history of human weaponry. When I imagined another race trying to “read” the symbolism, I thought they would be more likely to interpret the arrow as a rocket surface-blast and assume the flight, indicated on the plaque, was directed away from the spacecraft and toward the third rock from the sun.
David Adams, Aiken, S.C.

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Up a tree
Is it really surprising that A. afarensis could climb trees “Fossil puts Lucy’s kind up a tree,” (SN: 12/1/12, p. 16)? Or that children were more adept or did it more often than adults? Just because we evolved to walk upright doesn’t mean we can’t climb trees, just as the fact that we came out of the oceans several hundred million years ago doesn’t mean we don’t like to take a swim now and then.
Wayne Harris-Wyrick, Oklahoma City, Okla.

Researchers studying A. afarensis don’t see climbing and upright walking as mutually exclusive. The question is whether Lucy’s kind evolved to spend much of its time in the trees as a survival strategy rather than for occasional forays. This long-standing debate shows no signs of dimming. —Bruce Bower