Sunday, February 19, 2012


1st image) Cave painting made by the San people of eastern South Africa, who had lived in the Drakensberg Mountains for 20,000 years until they were killed and crowded out by colonists who arrived in the mid-16th c. 2nd image) Freddy Harteis, son of hunter Fred C. Harteis and host of the TV series "Hollywood Hunter," pictured with a chamois sheep he killed with a crossbow in New Zealand this spring.

Humans are apex predators. That we knew. But did you ever wonder why the animals we prey on have ceased to adapt the physical means to avoid being killed by us? Dr. Geerat J. Vermeij of the University of California-Davis has, and he has published his findings in a paper entitled "The Limits of Adaptation: Humans and the Predator-Prey Arms Race" in the current issue of Evolution. He lays out his thesis in the abstract:

"In the history of life, species have adapted to their consumers by evolving a wide variety of defenses. By contrast, animal species harvested in the wild by humans have not adapted structurally. Non-human predators have high failure rates at one or more stages of an attack, indicating that victim species have spatial refuges or phenotypic defenses that permit further functional improvement. A new compilation confirms that species in the wild cannot achieve immunity from human predation with structural defenses. The only remaining options are to become undesirable or to live in or escape to places where harvesting by people is curtailed. Escalation between prey defenses and predators' weapons may be restricted under human dominance to interactions involving those low-level predators that have benefited from human overexploitation of top consumers."

Our intelligence made up for the lack of big teeth, sharp claws, venomous bites, and other defenses. The artificial weapons we produced allowed us to become ever better hunters and start harvesting animals on a grand scale. The usual adaptations of prey - evolving to achieve greater speed, grow sharper teeth and horns, and form protective herds - don't seem to work against humans. Dr. Vermeij has been studying the effects of predators on evolution for more than 30 years and investigates why this is so. His main points are summarized by Matt Walker on his BBC Nature blog Wonder Monkey:
  • Growing larger doesn't help. Increasing to a size larger that a predator's mouth restricts them to preying on the weak and the young, but this doesn't work against tool-wielding humans, who hunt even huge blue whales. Their growth even worked to their disadvantage, since the quantity of meat that they would yield made larger mammals juicy targets.
  • Becoming toxic doesn't help. Humans have learned to remove toxins, that are often concentrated in organs such as the liver, and to avoid their ill effects.
  • Other protective adaptations don't help. The ivory tusks of elephants and large claws of lobsters and crabs made them liabilities rather than serving as deterrents against human hunters.
Our ingenuity (and greed, I might add) have resulted in the extinction of many species, for instance the dodo and the Tasmanian tiger, and the overharvesting of others, such as cod and tuna. In evolutionary terms, we leave our prey with nowhere to go. They have no way to defend themselves and simply cannot respond. “Our arrival and technological history has engendered an enormous change in the evolution of most species on Earth,” says Dr. Vermeij, and that represents a cataclysmic shift, the implications of which we have barely begun to understand.

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