Slijper's Goat
or
What a grotesque little beast
Sometimes during the 1920's, a darling little baby
goat was born without forelimbs. It barely even had
stubs. But we all know how
inventive and irrepressible goats are, so it comes as no surprise that this particular goat taught itself how to walk on its hindlimbs alone. Actually, it taught itself how to hop around, something like a
kangaroo does, only without a long, thick tail to use for balance. The animal lived for about year, and then it died in a freak accident.
I don't know how the goat got into the hands of Dr. E.J. Slijper, a
Dutch veterinarian. It's not impossible that Dr. Slijper was so eager to dissect the goat that he bought it from the gentle
farmer who had lovingly raised it, promised him that it would be treated kindly, and then gently shoved it down a flight of stairs. (Excuse me, it
fell.) But I do know that upon
dissecting the goat, Dr. Slijepr observed some fantastic differences between its
anatomy and the anatomy of a normal goat. Slijper's goat exhibited:
- Increased spinal curvature, resulting in an S-shaped spine; for a diagram, see <http://www.uhh.hawaii.edu/~ronald/393/Slijper-1.jpg>
- Dorsoventral flattening and elongation of the ischium
- Anterior extension of the gluteus muscle, reinforced by novel tendons
- A broadened neck
- Enlarged hindlimbs (obviously)
- A cylindrical thoracic cavity, instead of one that is V-shaped in cross-section
All of these changes are associated with the
evolution of bipedalism.
Slijper's goat raises interesting questions vis-a-vis the role of
phenotypic plasticity in the genesis of morphological
novelty. It exemplifies the fact that the gross
morphology of an animal's bone structure and musculature is only
indirectly predicated on that animal's genome. The proteins composing muscle and bones are genetically encoded, but they act in accordance with their
physical properties, resulting in the following trends:
Note that Slijper's goat only
seems to exemplify a case of the
Lamarckian inheritance. The atypical pressures that this goat faced altered its development, but not its genome. However, phenomena such as these force us to revise our conception of
selection. It's easy to think that bipedalism must have evolved because it was adaptive, and I'm not saying that it didn't. But it's not impossible that bipedalism evolved as a
trait that
hitchhiked on some actually adaptive trait, or even upon a
maladaptive trait that became
fixed within a population. Recall as well that bipedalism has evolved multiple times, among
ornithiscians (the taxa of
dinosaurs that includes birds), rodents, marsupials,
hominids, and others. There is no reason to assume that in each case the relevant
selection regime was not unique.
For further reference...
If you can read
Dutch, more power to you. Here's the original paper:
- Slijper, E.J. (1946). "Comparative biologic–anatomical investigations on the vertebral column and spinal musculature of mammals". Verh. Kon. Nederl. Akad. Wetensch. Amsterdam II 42, 1–128.
Otherwise, you'll just have to trust my sources:
- McCune, A. "Development and Epigenetics". Lecture delivered at Cornell University, 15 April 2004
- Myers, P.Z. "Two legged goats and developmental variation." Pharyngula, <http://pharyngula.org/comments/A53_0_1_0_C>, accessed 16 April 2004.