Friday, January 4, 2008

The Irish Elk (neither totally Irish nor an Elk)...

Of all the extinct mammals I knew of as a child, Megaloceros was the most memorable. I remember turning the pages of a glossy picture book and seeing, for the first time, the huge antlers and strong body of the animal. I was in awe. When I visited the AMNH over my winter vacation I saw my first Megaloceros skeleton and I was no less impressed.

What's even more impressive is the amount of involvement Megaloceros has had in evolutionary debate.

Picture from http://www.arcticwebsite.com/

Megaloceros, or the "Irish Elk," was first described in 1697 by Thomas Molyneux, who,
being a man of his time, believed that it was extant. Eventually, the Irish Elk was used by Georges Cuvier to demonstrate that extinction did in fact occur.

Megaloceros was also used as an example in the theory of orthogenesis. Proponents of orthogenesis, according to Stephen Jay Gould, "claimed that evolution proceeded in straight lines that natural selection could not regulate. Certain trends, once started, could not be stopped even if they led to extinction." The antlers of the Irish Elk seemed to validate the theory. The animal evolved from smaller deer featuring small antlers and eventually, its antlers became so over sized that the deer could no longer function. Orthogenesis attributed the extinction of Megaloceros to the bulk of its head ornament. Unfortunately, modern creationists use the Irish Elk as an argument against natural selection.

The size of Megaloceros's antlers, according to Gould, can be attributed to allometry or proportional growth. He rejects the idea that the antlers outgrew their purpose. Gould says, "I believe that the supposed problem of "unwieldy" or "cumbersome" antlers is an illusion rooted in a notion now abandoned by students of animal behavior."

Gould proposed that the antlers were used for display. Their size was actually an advantage: larger antlers conveyed higher status and dominance. The increasing size of the antlers alternately caused an increase in the body size of the deer and, as Gould expresses below, also explains the morphology of the antlers.

As devices for display among males, the enormous antlers of the Irish Elk finally make sense as structures adaptive in themselves. Moreover, as R.Coope of Birmingham University pointed out to me, the detailed morphology of the antlers can be explained, for the first time, in this context. Deer with broad-palmed antlers tend to show the full width of their antlers in display. The modern fallow deer (considered by many as the Irish Elk's nearest living relative) must rotate its head from side to side in order to show its palm. This would have created great problems for the giant deer, since the torque produced by swinging the ninety-pound antlers would have been immense. But the antlers of the Irish Elk were arranged to display the palm fully when the animal looked straight ahead. Both the unusual configuration and the enormous size of the antlers can be explained by postulating that they were used for display rather than for combat.
I, for one, am thoroughly impressed with Gould's writing and thinking. His essays are packed with information and easy to read, though not dumbed down at all. My immediate reaction to his writing is to think warmly of him and somewhat idolize him. I understand that some people disagree with much of Gould's thinking and that many actively oppose him. I'd love to know more about it. What do you think of Gould? Why?

REFERENCES
Gould, Stephen Jay. 1977. Ever Since Darwin: Reflections on Natural History. New York: W.W. Norton & Company Ltd.

2 comments:

Zach Miller said...

I like Gould a lot, although he can come off as a little bull-headed at times. I very much appreciate his writing style. He manages to be informative and scientific, but in a way that most people can understand.

Megaloceras is one of my favorite ice-age mammals. My dad would love to bowhunt it, I'm sure. :-) And here's a fun little corruption of the name to say:

Megaloceraceras! (MEGA-LOSS-ER-OSS-ER-US)

Anonymous said...

have you seen http://blog.wired.com/gadgets/2007/12/dinosaur-abuse.html?