The Allure of Big Antlers

By Carl Zimmer | September 3, 2008 1:09 am

irish-elk-220.jpgI can’t help finding the Irish elk wonderfully ridiculous. The reaction probably has something to do with the fact that we are all familiar today with deer, moose and other animals that look for the most part like the Irish elk, except for that extravagant rack. Irish elk grew the biggest antlers ever recorded, stretching over ten feet across and weighing about 90 pounds. Of course, for the people who lived alongside the Irish elk in Europe and Asia before its extinction 7000 years ago, it probably didn’t seem terribly ridiculous at all–no more ridiculous than an orangutan or a river dolphin look to us today. And the way things are going, orangutans and river dolphins may not be long for this world. After they’re gone, people will look back at pictures of them the way we look at pictures of the Irish elk, and imagine they were just made up by a bored zoologist.

The antlers of the Irish elk have long obsessed zoologists, bored or otherwise. In the late 1800s, many scientists believed that evolution proceeded in straight lines, with too much momentum to be steered off course by natural selection. The Irish elk was a prime example of this straight-line evolution known as orthogenesis. Evolving from small ancestors, they grew to be giants. Their antlers grew larger still. While they may have been useful at first for keeping away predators and such, orthogenesis could not be stopped. The poor Irish elk ended up burdened with massive headgear that got them stuck in thickets and drove them extinct. (For more, see this essay by Stephen Jay Gould.)

Orthogenesis fell apart in the early 1900s, as scientists began to learn how genes make natural selection possible. The Irish elk was not a victim of some mysterious inner momentum. Its antlers simply evolved to be bigger at a faster rate than its body.  A big body helped Irish elk survive, and the bigger antlers were just an unavoidable–but manageable–inconvenience.

When Gould wrote his essay in the mid-1970s, scientists were just beginning to recognize that antlers had important functions of their own beyond just warding off a wolf. They were signals. Big antlers in living deer are a sign of a high-quality male–a male that can fight off other males for territory, and that may be able to attract females. Today there’s a lot more evidence supporting the idea that antlers are driven by sexual selection, not natural selection or orthogenesis.

The funny thing about this story is that hypotheses about the extinction of Irish elk have come back to those doomed antlers again. Playing the role of orthogenesis now is the relentless power of sexual selection. The antlers got bigger and bigger as the Irish elk stags advertised their quality. Each year they lost these monstrous growths and regenerated them the following year. As the shrubby woodlands in which the Irish elk lived began to shrink at the end of the last Ice Age, the animals could no longer get enough food to fuel those giant antlers, and they died. Sexually selected suicide, in other words.

This always seemed a bit odd to me, but I didn’t see much research from scientists that took a critical look at the idea. Recently, though, a University of Florida graduate student named Cedric O’Driscoll Worman noticed this picture of an Irish elk proudly displayed on the front page of my web site.  It turns out he is a devotee of Megaloceros giganteus as well, and he sent me his new paper with Tristan Kimbrell in the journal Oikos. There, they take aim at the notion of the doomed antlers.

Worman and Kimbrell argue that even with the advantages that some with a fancy set of antlers, the Irish elk could have easily shrunk them if they didn’t have enough food. They point to red deer that have adapted to living on predator-free islands, where they shrank to half the size of their mainland ancestors. Their antlers shrank far more. Antlers can get small even without an evolutionary shift–if red deer suffer overcrowding and run low on food, their antlers can lose almost a third their weight. Feeding stags extra food can double the size of their antlers. If an Irish elk stag responded to a lack of food the way red deer do today, their antlers would shrink down to the size of moose antlers or less. Obviously moose have managed to survive with antlers that size, so Irish elk should have as well.Worman and Kimbrell argue that even if stags with big antlers died off, there would have been plenty of males with smaller antlers to take their place. And in a species where a few males probably fathered most of the offspring each generation, a lot of stags would have to die off before the species as a whole began to suffer. Hunters today show this to be the case–populations of deer can handle a lot of killed stags. But the does are another matter.

And it’s the does that Worman and Kimbrel think we should think about when we think about why the Irish elk are gone. The long, graceful legs of Irish elk suggest that they were fast runners that could cover long distances. The females needed a lot of energy during pregnancy and nursing, so their offspring would be ready to run with the herd from the get-go. Fast running may have been the only way to survive the dire wolves and other predators that hunted Irish elk. Other deer could respond to the limited food on small islands by getting small. But the predators Irish elk faced did not allow that strategy. The females were stuck, trying to produce big offspring with less food. As a result, Worman and Kimbrel propose, their numbers dwindled. In some places, humans may have hastened their death with hunting, but the Irish elk vanished from Ireland long before humans arrived.

If Worman and Kimbrel are right, their disappearance had little to do with their antlers. Those giant signals may actually be a beautiful distraction from the real cause of their extinction. Not sexual suicide, but just the struggle to produce healthy young.

CATEGORIZED UNDER: Evolution

Comments (8)

  1. Nice piece Carl. I grew up in Ireland and was always impressed, as a child, with the collections of Irish Elk in the various local museums and the various stories that were told about them.
    It was only much later that I became interested in the science behind it and realized that a lot of the things taught in school couldn’t be true.
    I think the natural history of Ireland over the past 15 thousand years illustrates an important point that I haven’t really seen discussed before in a simple, easy to understand manner, and which has important resonances with today’s climate changing environment.
    One truly startling thing for me to realize was that the actual geographic location where these Elks, and many other ‘Irish’ organisms lived at the height of the last ice age, 15,000 years ago, only partially overlapped the land of the current island of Ireland. Have a look at the maps on the page linked below and you’ll get an idea of the effect that temperature change had on the map of Europe. Perhaps there were huge herds of Elks roaming the lost plain between Ireland and Brittany and the museum skeletons are simply those of the last stragglers that escaped the rising tides.
    http://www.rootsweb.ancestry.com/~irlkik/ihm/ancient.htm

  2. JAMESM

    “The females were stuck, trying to produce big offspring with less food…”

    Exactly.

    For females assessing the desirability of a mate, the size of the antlers is an ideal measure of the male because growing antlers is a direct proxy for growing a fetus.

    Antlers grow from nothing to an enormous size in a short interval during the breeding season, just as the fetus does, and they are made of the same materials as the bones of the fetus. A male with enormous antlers is therefore more likely to be able to sire cows which can gestate big calves with big strong bones than a lesser-antlered male.

    If it’s true that Irish elk had to be long-legged and fast to outrun predators, then their most vulnerable stage of life, as calves, must have had to have had really spectacularly long and strong legs. That in turn means that during the limited time in the period of gestation when the legs are growing, there must have been tremendous demands on the mother to be able to produce the minerals and other nutrients the calf needed for those exceptional legs, and the female calves sired by males with the biggest antlers could be expected to have the greatest success meeting such demands when their own time came.

    I sometimes think evolutionary biologists do not spend enough time looking for specific adaptive functions for the exaggerated male phenotypes produced by sexual selection by imagining what the characteristic selected for (huge antlers in this case) would mean when translated– mutatis mutandis– into the characteristics of his female offspring (ability to gestate big fast calves, in this case).

    From this point of view however, I am forced to disagree that “their disappearance had little to do with their antlers.” I would say that the enormity of the antlers is a signal to us, just as it was to the female elk, of runaway selection pressure that the Irish elk could finally not keep up with.

  3. Monkey

    Carl, do you mean that antlers “shrink” or over generations they reduce in size/weight? Confused on that issue, because:

    1) IF they shrink/grow on a single individual over the course of a season, is that not a reflection of health and not a genetic trait that could be beneficial? Like my bones getting stronger and weaker base don my general health?

    2) If the generational diferences are what is meant, that makes sense.

    3) A stag with good food resources will grow larger antlers than one with poor resources. Is this what you meant?

    Sorry, simple issue her about simple biology but one that has my mind in a knot while trying to digest this. The rest made perfect sense, its just that little itty bit.

    Good stuff, though. I found your site a few weeks back via the mighty world of links, and havent left yet. Stuff like this makes my brain happy!

  4. Interesting perspective. I thought dire wolves were exclusively American, while Megaloceros was European?

  5. Great article on a beloved creature! I remember seeing the familiar Megaloceras skull at every museum in Europe while I was traveling around.

    I found your blog through the latest edition of the Boneyard blog carnival. Keep up the great work!

  6. Rhonda

    Amazing! I am interested in having a replica set of Irish Elk Antlers created. Do you know if this would be a possibility?
    Or better yet, can you tell me if sets of Irish Elk Antlers are ever available to purchase? Thank you!

  7. PLENG

    great but if you can found out about cave bear and/ short faced bear
    great job
    thank you for the comment

  8. Responding to Rhonda who submitted a query on Apr 22nd ’09: “Amazing! …I am interested in having a replica set of Irish Elk Antlers created. Do you know if this would be a possibility? Or better yet, can you tell me if sets of Irish Elk Antlers are ever available to purchase? Thank you! ”

    I recently wood-crafted a replica set of “Irish Elk” antlers, complete with head, for a buyer in TN. This particular speciman had a 12′ rack. I designed it so the two antlers and head (including teeth) could be transported and assembled on site. Prices range from $4000. – $7000., depending on width. (delivery and placement may be arranged)
    Please contact Bob McGavock at Horsin’ Around Carousel Carving School ,(423) 332-1111 or cell (423) 667-2960 in Chattanooga,Tn.

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The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.

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