Hunting Big Game Speeds Evolution of Shrinking Species

By Nina Bai | January 14, 2009 7:27 am

headsThe human penchant for animals of impressive size has left some of the most hunted species smaller and weaker. A new study finds that human-induced selection, through activities like hunting and fishing, is having a profound effect on the evolution of many species. “Human-harvested organisms are the fastest-changing organisms yet observed in the wild” [National Geographic News], said lead researcher Chris Darimont. The pattern of loss to human predation like hunting or harvesting is opposite to what occurs in nature or even in agriculture [The New York Times]; instead of survival of the fittest, human predation encourages survival of the scrawniest.

In nature, predators typically take “the newly born or the nearly dead,” Dr. Darimont said [The New York Times], because healthy individuals are more difficult and dangerous to catch. But human hunters and gatherers target the biggest and strongest individuals. To find out how human predation affects species evolution, researchers examined previously documented, hunting-induced changes across 29 species in 40 locations, including commercially targeted fish, bighorn sheep, caribou, and several marine animals such as limpets and snails. Two plant species were also included in the analysis: Himalayan snow lotus and American ginseng [National Geographic News]. The hunted species were compared with 25 species that are not hunted but subject to other human interference and another 20 species that face only “natural” pressures, such as climate, competition for resources, or animal predators [National Geographic News].

All three categories included some rapid modifications, so “comparing the databases was kind of a showdown,” Darimont says [ScienceNOW Daily News]. Reporting in the Proceedings of the National Academy of Sciences [subscription required], the researchers found that hunted species won the showdown—evolving 50 percent faster than those facing other human interference and three times faster than those not affected by human activities. Species exploited by humans showed a general trend of evolving smaller body size and breeding at a younger age. The body and horn sizes of bighorn sheep, for example, have declined by about 20 percent in the past three decades as a result of human hunting. Atlantic cod on the east coast of Canada now breed at five years of age instead of six—a shift that has occurred in only two decades [National Geographic News].

Since trophy hunting removes the strongest individuals from the gene pool, the breeding populations left behind become progressively smaller and younger. Researchers are concerned that these younger populations may not be able to reproduce as well. Darimont says that in fish especially, “younger and smaller breeders produce less offspring, and this jeopardizes the ability of prey species to recover after harvest.” Such shifts may also imperil other species that have evolved alongside the targeted animals, either as predators, prey, or competitors, Darimont added [National Geographic News].

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Image: flickr / jensweb

  • Chubbee

    I find it amazing that our great scientific minds are just figuring out what has been obvious all along.
    But I guess since nobody did a “study” on it, common sence assumptions don’t count.

  • Jumblepudding

    I always thought the ideal was that the largest, fittest individuals were the most successful at mating and had already produced several offspring over the years by the time they were picked off, thus passing on their genes. This simply proved that is nonsense. Bravo to your common sense, though.

  • saoirseglen

    What I find amazing is that if this were the case, why do we continue to have large animals still in the ecosystem? By the logic in the article there should be nothing but dwarf animals that are weak. From what I have seen in personal experiences, there is no lack of trophy type animals.

    This is spoken from a conservationist and hunting standpoint. There is also no shortage of wildlife in my area, if anything, they need to have the populations reduced so that they do not become weak and sick from overpopulating the available resources.

    I see the animals with my own eyes and I don’t simply take words at their value.

  • GrapeCoolAid

    If only all the cool aide tasted this good.
    What a bunch of crap.
    Ok, so there is a little merit if they attributed this kind of thinking in a commercial hunting/fishing aspect, but not with recreational hunting and fishing. They are apples and oranges but to a fruitcake it’s probably all the same.
    As a freediver I spend a lot of intimate time under water.
    There are plenty of big fish to be found, however the largest are also the most wary, go figure. Its one of the reasons record-breaking fish are taken almost annually.
    I wish the people who orchestrate these studies were not so biased in the first place, taking their work and melding it into something far from the truth.
    The fact of the matter is people hunt and fish for more than just a mount on the wall. There will always be the jerk offs that hunt for trophies, but the true hunter/fisherman is the one that respects their prey more than any non-hunter/fisher would ever understand.

  • sg

    Chubbee: This is exactly why science has rapidly transformed the world over the last few centuries: “Common sense” often proves to be wrong if one has an incomplete understanding of something. What objective data do is create a more accurate picture. Many things that science discovers are counter-intuitive. Your under-appreciation of the complexity of the world belies great ignorance.


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