Example of natural selection in animals

We usually think of evolution as something we don't see happening right before our eyes, instead looking at fossils to find evidence of it happening in the past.

In fact, evolution under intense population pressure happens so fast that we've seen it occur within the span of a human lifetime.

Elephant Tusks

African elephants typically have large tusks. The ivory in the tusks is highly valued by some people, so hunters have hunted and killed elephants to tear out their tusks and sell them (usually illegally) for decades.

Some African elephants have a rare trait: They never develop tusks at all.

In 1930, about 1 percent of all elephants had no tusks. The ivory hunters didn't bother killing them because there was no ivory to recover. Meanwhile, elephants with tusks were killed off by the hundreds, many of them before they ever had a chance to reproduce.

The alleles for "no tusks" were passed along over jus