A new “geep,” a sheep/goat hybrid

August 3, 2014 • 5:11 am

I had long thought, and even taught, that sheep and goats couldn’t form viable hybrids, as they are very distantly related. Timetree puts them at a divergence of about 7 million years, which is the equivalent of a human and a chimp producing a viable offspring. (It’s been tried, believe me, and it doesn’t work. See WEIT for details.) I would sometimes tell students that cross-fertilization between the species produced hybrid embryos that would die early in development, an example of species distinctness enforced by “hybrid inviability.”

It turns out that’s largely true, but not entirely. Reader Merilee sent me a picture of a newborn  geep, an apparently healthy hybrid between the two species. That led me to a news website in Arizona that published a piece on a newborn geep on August 1 and showed and a video of the cute little thing. Here are the facts:

Butterfly may be Arizona’s only geep, a tiny tot with goat hooves and a goat head, but covered in wool. Her mom, Momma, is a sheep. Her dad, Michael, is a pygmy goat. Hence, geep. She was named Butterfly for her spots.




As expected, Wikipedia has a good piece on the hybrids. It says, among other things, this:

A sheep–goat hybrid (sometimes called a geep or toast in popular media) is the hybrid offspring of a sheep and a goat. Although sheep and goats seem similar and can be mated, they belong to different genera in the subfamily Caprinae of the family Bovidae. Sheep belong to the genus Ovis and have 54 chromosomes, while goats belong to the genus Capra and have 60 chromosomes. The offspring of a sheep-goat pairing is generally stillborn. Despite widespread shared pasturing of goats and sheep, hybrids are very rare, indicating the genetic distance between the two species. Though sometimes called “geep”, they are not to be confused with goat-sheep chimerae, which are artificially created.

Knowing nothing about geeps, I would have guessed that any viable ones would be female (and probably sterile), in accordance with Haldane’s rule: the generalization that if only one sex of hybrids between species is either viable or fertile, that sex is almost invariably the “homogametic” one: the one with similar sex chromosomes. Since male mammals are the “heterogametic sex” (XY) and females are the homogametic (XX) sex, I’d expect geeps, if viable, to be female, and to be sterile because of the evolutionary distance between the parental species.

An aside: I worked on Haldane’s rule for much of my career, as it’s one of the few “laws” of biology–i.e., generalizations that are rarely violated–and for many years my students and I sought a general explanation for a phenomenon seen not only in mammals and insects–males heterogametic– but also in  birds and butterflies, groups which females are heterogametic and in which, in accordance with the rule, females are the sterile or missing hybrids. We think we have a good explanation for Haldane’s rule now, but if you want to read about it, see chapter 7 of Speciation by Coyne and Orr. It’s technical and a bit complicated.

Well, Butterfly is female, but we don’t yet know about her fertility. But Wikipedia suggests that Haldane’s rule has been violated in these species–the geep was both female and fertile.

On May 12, 2011, a healthy and fertile geep was born in Bant, Flevoland, the Netherlands. The geep mated with a ewe and on December 25, 2012 two healthy lambs were born.

Below is a video of a geep born on a farm in Ireland, and you can find pictures of other hybrids here. I expect reader Linda Grilli to weigh in soon, as she keeps goats and also rises very early. She will, I hope, tell us more about geeps, or about this hybrid.

18 thoughts on “A new “geep,” a sheep/goat hybrid

  1. Sorry, no information here.

    I have raised sheep and goats, but never at the same time. My knowledge of genetics is pretty much species-specific, and limited to selective breeding. L

  2. Sheep/goat hybrids have a long history. The ancient greeks called the offspring of male sheep and a female goat “musimones”, while “umbri” is the inverse.

    John Baptist Porta, in his quite amusing 1584 pop-science book “Natural Magicks” has a section on them:

    Alfred Russel Wallace also has a section on them in his 1889 book “Darwinism”: http://en.wikisource.org/wiki/Page:Darwinism_by_Alfred_Wallace_1889.djvu/185

  3. I personally don’t think enough effort has gone into human-chimp hybrids. I know there was an attempt to artificially inseminate a small number of female chimpanzees back in the late 20s, but it doesn’t seem like enough to rule out the possibility.

    You’d think that it could be attempted without creating too much of an ethical problem by attempting to combine a fairly large number of human sperm and chimpanzee eggs and vice versa in vitro and seeing if any eggs become fertilized.

    I suppose there’d be little use for it, but I’m very curious about the possibility…

    1. Yes, and as far as I know it could work. Other experiments have confirmed that human sperm can initiate fertilization of gibbon eggs in vitro.
      But a serious effort to make a humanzee would be seriously unethical.

    2. I know there was an attempt to artificially inseminate a small number of female chimpanzees back in the late 20s,

      I was seeing a report from Indonesia a while ago that human-orangutang interbreeding efforts were continuing. At least one brothel (for paying humans) had acquired a female orang and were making it available for their less inhibited customers.
      I’d be moderately surprised if the same hadn’t been tried in Africa, but I’ve never heard a hint of a success.

  4. On May 12, 2011, a healthy and fertile geep was born in Bant, Flevoland, the Netherlands.

    Locally that would be a gaap or a scheit, then. Neither of which sounds very flattering.

  5. I think that more confirmation of the hybrid origin of Butterfly than a news piece is needed (recall the “cabbits” that periodically appear on local and even national news). As Richard van Gelder wrote in an analysis of intergeneric hybridization in mammals, “Hybrids between goats (Capra) and sheep (Ovis) have long been reported, but seldom adequately documented.” Van Gelder, did, however, accept that some reports were genuine, including a female hybrid that was fertile when artificially inseminated with sheep semen (which agrees with Haldane’s Rule). The locus classicus for the documentation of mammalian hybrids is Annie Gray’s 1972 Mammalian Hybrids: A Check-list with Bibliography (Revised edition. Commonwealth Bur. Animal Breeding and Genet., Edinburgh).

  6. I read elsewhere that hybrids such as mules are typically sterile when mated with each other, but can be fertile when cross-bred again with one of their two parent species, and after some number of such events, a fertile hybrid species can be obtained. If true, as it seems to be in at least some cases, this is another mechanism that evolution can use, and probably has used, to produce its amazing results.

    It could also explain some mythological creatures – but probably not.

  7. there are some more hybrids as well, such as Beefalo/Wholfin/Zonkey/Leopon/Liger . On the issue of Human Chimp.. Im sure if they give it enough tries it would happen. If a goat and a sheep could do this with drastically different chromosome counts. I see no reason why a rare hybrid would be out of the question. Ofcourse ethical issues are at stake here.

    1. Zorses and possibly Heberas, between horse and zebera, too. I’ve only seen the “Zorse” name in the literature though ; which parent sex was which species wasn’t reported.

  8. Hey Jerry,
    I would love to read ‘Speciation’, but the price was too steep. Any chance of a lower price someday?

  9. “Rates of conception from this cross are much higher with ram semen than with goat (but still much lower than in non-mixed matings). In fact, Shelton (1993) says that “When a male goat is mated to a female sheep, conception does not, in general, occur. The apparent explanation is a failure of sperm transport due to immunological antagonism. If a male sheep is mated to a female goat, conception will occur in a large number of cases, but the conception rate of 30-50% is below that of intra-species mating. The normal result of mating a male sheep to a female goat is a hybrid embryo which dies in the 40-50 day range, with some surviving for a more extended time.”

    More about geeps and a huge list of many other types of mammalian hybrids here.

    1. The website on mammalian linked to in this comment is unreliable, and nothing in it should be accepted without independent confirmation. The site’s proprietor is infamous for proposing that humans are the result of chimp-pig hybridization. (That’s right– pig!!)

  10. It is interesting then that there is often such difficulty for archaeologists (or was) in telling apart sheep & goat bones.

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