Natural selection gets help from humans

updated 6:15 p.m. ET July 4, 2005

WASHINGTON - When Charles Darwin explained evolution, the process he observed was natural selection. It turns out inadvertent human selection can also cause species to evolve.

Take the case of the snow lotus, a rare plant that grows only at high levels in the Himalayas.
Researchers have discovered that one species of the plant has been shrinking over time — the one people like to pick.

A snow lotus species called Saussurea laniceps is used in traditional Tibetan and Chinese medicine and is increasingly sought after by tourists. The largest plants are picked, and that occurs during their only flowering period.

The result is that only smaller, unpicked plants go to seed.

“Selection caused by humans is a powerful force, whether conscious or unconscious, artificial or natural,” Wayne Law and Jan Salick of the Missouri Botanical Garden in St. Louis commented.

They studied specimens of the plants picked over time and also compared S. laniceps growing in heavily harvested areas with those found in places where people rarely picked them.

They report in Tuesday’s issue of Proceedings of the National Academy of Sciences that the heavily harvested snow lotuses have been getting shorter over the last century, while those in areas not picked have not shrunk.

And, they noted, a second species, S. medusa, which is not often picked, has not been changing.

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In the heavily harvested areas, where only the smaller plants got to reproduce, the S. laniceps averaged 5.3 inches tall, they found. The same plants in rarely harvested areas averaged 9 inches in height.

“Paradoxically, with unconscious human selection, when a species possesses a certain trait that is valued by people, individuals with that trait will be preferentially harvested and this selection will leave individuals with less desirable traits,” Law and Salick pointed out.

The research was supported by the National Science Foundation, the Mellon Foundation and The Nature Conservancy.

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