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Thinking zebras… and horses

June 9, 2021 0 Comments

“When you hear hoofbeats, think horses, not zebras”

This post first appeared on August 4, 2011
I have been thinking about zebras lately. Part of the reason is probably best left for another post, since it’s a different tangent than this one. As readers of the studio blog know, I tend to wander off on tangents a lot. I do eventually get back to where I was, though it often takes a while. Oddly enough, this will bring us back to Dominant Whites, though a bit indirectly.

The other reason is that I recently ran across my copy of the Penycuik Experiments by Professor James Ewart. The Penycuik Experiments were conducted in the late nineteenth century. I originally found the book when looking for information on the Highland Ponies of Rhum, which are interesting because they are associated with the silver gene as well as the “tiger eye” trait. The text proved to be a dead-end for that, but the experiments described were really cool. I thought it might be fun to share them here, in part because the hybrids are interesting and in part because the experiment itself is a wonderful illustration of just how far we have come in our understanding of genetics in the last 100 years.

Professor Ewart was interested in disproving the theory of telegony, which was the belief that offspring from a cross could be influenced by the traits of the mother’s previous mates. While this might seem quite silly now, at the time the idea was almost universally accepted. Darwin mentions it in The Variation of Animals and Plants under Domestication, citing a case where a mare was crossed on a quagga and later produced horses with striping. The Penycuik Experiment was an attempt to recreate that situation to see if the theory of telegony held. The experiments are particularly interesting in that they predate the re-discovery of Mendel’s work by a few years.

The last quagga died in captivity in 1883, so Ewart used a Burchell Zebra stallion, Matopo. He crossed the Matopo, who is pictured at the top of the post, with a wide variety of mares. Among the first of the hybrid foals was Romulus, from the black Highland mare, Mulatto.

Most of the other hybrids looked much like Romulus – reddish brown ground color with an overlay of black stripes. Ewart also includes photos of the zebra hybrid bred by Lady Meux. In that case a Burchell’s zebra mare was crossed with a “Highland or Shetland Pony” with wall eyes.

He was said to be “light bay”, but in the photos above he looks chestnut. Unlike the other hybrid foals, his daughter does not have particularly visible striping.

She also looks like she might be chestnut, though it is hard to tell from an old black and white photograph. Another zebra hybrid, Birgus, was said to have grown up to be chestnut with black stripes. He was by Matopo and out of a chestnut polo pony mare. Photos of modern zorses suggest that in addition to black striping, the chestnuts also have black lower legs much like a wild bay.

What is interesting is that none of the hybrids in the Penycuik study had white markings of any kind. In addition to the wall-eyed pony stallion, one of the mares used by Ewart was a Clydesdale mare. White patterns can trump the zebra striping, which many have seen with the well-known tobiano zorse Eclypse.

The interesting thing about Romulus, and indeed all the other zebra hybrids, is that they had more stripes than their zebra parent. Ewart counted 43 stripes on Romulus, compared to the five between the shoulder stripe and hindquarter for Matopo. That seems counter-intuitive, that crossing an unstriped animal with a striped one might give the resulting offspring more stripes. That brings me to the other tangent I mentioned earlier. Tomorrow I’ll post about embryonic development and spot frequency, because that’s more really cool stuff.

By lkathman

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