This week’s post is from Katrina van Grouw, a scientist, illustrator, author and more. If you would like to write for Anatomy to You, get in touch via Facebook or Twitter.
Anyone who’s read On the Origin of Species will know that it begins with—pigeons.
Domesticated pigeons. Pages and pages of them.
As a teenager I laboured through the first chapter with mounting disappointment, before consigning Origin to the bookshelf in disgust. I wanted to learn about adaptations in wild animals, about peppered moths and pocket mice and all the things you can find in modern textbooks. Pigeons were synonymous with town centres, or with old men in flat caps.
But Darwin had been especially clever in beginning Origin in this way. The theory he was presenting shows a mechanism by which all the diversity on the planet could have come into existence without the need for a divine creator— a frightening concept to the Victorian mind. Everyone kept livestock, however, so by beginning his book in this way Darwin could settle his audience in their comfort zone before delivering the fatal blow.
While evidence in wild animals appeared inconclusive, he had observed how quickly anatomical changes could come about in domesticated animals. Darwin kept pigeons for several years and could witness at first-hand how readily they reproduce and how necessary it is to control populations. Retaining those individuals with desirable qualities could, he observed, within just a few pigeon-generations, result in radically altered birds.
One of the pigeon breeds he kept was the fantail. The conformation that Darwin would have been familiar with can still be seen in garden dovecotes: a rather horizontal body posture, sloping tail, and neck held in an elegant, swan-like S-shape pushing the breast forward.
Fast forward a little over 100 years to the 1970’s and fantails kept for exhibition would look very different. Fanciers increasingly selected birds for a more erect posture, gradually rotating the entire body to a near vertical position. The orientation of the thighs remained roughly horizontal but instead of lying on either side of the ribcage they now spanned the depth of the abdomen. The neck became more tightly curved too, sweeping so far back that the vertebral column evolved a slight concave dip to accommodate it. Birds in the most extreme show positions would frequently stand on tiptoe to maintain their balance. (I should mention here that even the more extreme birds only adopt these poses when they’re excited—they can still carry out all their natural functions).
But it doesn’t take a century for change to happen. Modern exhibition fantails are again changed, this time with the body tilted forward again toward the diagonal but also sunk lower, bringing the knees up above the level of the thighs. The neck remained swept back cushioning the head just above the rump, with the tail now held perfectly erect and spread. The whole bird has taken on rather spherical proportions.
No-one selects on skeleton shape, remember—they select on external appearance, in this case the best way to show off the lovely tail (which was meanwhile undergoing evolution of its own). The skeleton is simply moulded into the desired conformation as a consequence.
As Darwin observed, animals are plastic things, and domesticated animals offered not just an analogy for evolution, but a perfect example of evolution in action.
For more about Katrina van Grouw’s work, including her recent book “Unnatural Selection” where the above images came from, see her website here.
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