Megaloceros and orthogenesis

Megaloceros on display at AMNH

Megaloceros, commonly (and wrongly) known as the “Irish Elk” offers a good example of an organism utilized as proof of orthogenesis during the latter half of the 19th century and the early 20th century.  During this period, paleontologists utilized the term “orthogenesis” to explain trends in the fossil record.  Under the model of orthogenesis, once a species begins to develop, it continues to develop along that line and exhibits an inability to stop this process of development.  In the case of Megaloceros, the argument was structured such that through the process of orthogenesis, Megaloceros’ antlers grew to extreme sizes.  Ultimately, this unchecked antler growth caused the extinction of Megaloceros.  This example offers a good model to demonstrate why orthogenesis does not work.  A trait isn’t going to survive if it causes a problem for the survival of the organism in question.  Ultimately, even if selective pressures do support the development of larger antlers in Megaloceros, the antlers won’t get large enough to cause extinction.  If an individual Megaloceros has antlers so large that they end up getting caught in trees (part of the orthogenesis argument), then it’s not going to have much success with reproduction. Sure, a few individuals with extremely large antlers might get to reproduce, but as a rule, most of these will, in fact, be weaned from the gene pool.  This is why orthogenesis does not work.

If you’re interested in this topic, check out Stephen Jay Gould’s article “The misnamed, mistreated, and misunderstood Irish Elk.” The article is available in his 1977 book Ever Since Darwin.

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Explore posts in the same categories: 1800s, 1900s, evolution, geology, history of science, paleontology

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