From MSNBC:
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.
More here.