Natural selection gives way to human selection

Humans have become "superpredators," speeding up the evolution of the species they hunt and harvest at rates far above what is found in nature, according to new research, some of it conducted by Canadian biologists.

The researchers believe that many recently observed changes in species, ranging from the shrinkage in the horns of bighorn sheep in the Rockies to the reduction in the size of caribou in Scandinavia, are being driven by humans.

The biologists estimate that hunting has caused such characteristics as body size and reproductive age to change at a rate that is a staggering 300 per cent above the pace that would prevail in nature. This figure is even greater than the change attributed to other human interferences, such as pollution, which was estimated to alter species 50 per cent faster than what normally happens.

"The implications are pretty wide and profound," said Paul Paquet, a University of Calgary biologist who dubs humans "superpredators" for this outsized impact.

A paper outlining the findings was posted yesterday in the online edition of Proceedings of the National Academy of Sciences.

In it, Dr. Paquet and others argue that current hunting and harvesting practices are inadvertently causing dramatic changes in the behaviour and appearance of species. The reason: Humans tend to "high-grade" nature, taking out the biggest and best in a species.

The approach is clearest in trophy hunting, where animals with the biggest horns or bodies are killed, while inferior ones are left. But the practice also occurs in commercial fishing, where mesh openings in nets capture the biggest fish while smaller ones escape.

The human approach is the opposite to what happens in nature, where predators kill the easiest-to-catch animals, such as the young, the old and the sick, but are unable to take out the fittest adults, which then reproduce and pass their desirable characteristics on to future generations.

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