The Frontal Cortex

Mules are Smarter

A mule is a biological hybrid, an offspring of a male donkey and a female horse. According to a new paper, all of this cross-pollination has real benefits: mules are significantly smarter than either of their parents. No regression to the mean here:

Six of each animal were shown sets of two food buckets, each marked with a different symbol.In order to gain access to the food, the animals had to pick the correct bucket. The mules learned to discriminate between more pairs of symbols than the horses or donkeys, and did so more consistently.

The scientists argue that the intelligence of mules results from their genotypic diversity. It’s long been recognized that such diversity can produce improved physical characteristics – mules are also stronger than their parents – but this study suggests that diversity also has cognitive benefits. And there’s no reason to think that the hybrid principle is limited to mules. So go out and rescue a mutt and marry somebody with an entirely different set of recessive genes.


  1. #1 Dhea
    July 31, 2008

    I am a little confused about how increased diversity results in greater physical and mental capacity? Is it because each gamete donor of the hybrid provides different capacities which work together to produce overall improvement in skills? And why would the attributes have to be recessive? I am sorry if this is a ridiculous question but I actually want to know the answer?

  2. #2 Spaulding
    July 31, 2008

    Dhea, you can read up on two mechanisms for “hybrid vigor” here:

    Seems to me that codominant alleles could also contribute.

  3. #3 Ben_Wraith
    July 31, 2008

    What’s a good way to determine that someone you’re going to marry has significantly different genes?

  4. #4 Dhea
    July 31, 2008

    Thanks Spaulding, much appreciated!

  5. #5 Luna_the_cat
    July 31, 2008

    Having dealt with donkeys, horses, AND mules for the first part of my life, in Colorado, I would tell you without hesitation that this comes as absolutely no surprise to anyone who has dealt with these creatures. This is one of those situations where research absolutely echoes everyday common experience, for once. Mules are smart.

    And cunning. Damn cunning.

    If a mule likes you, you will never have a better pack animal, and they will deliberately help you out, and you can trust them absolutely to find footing anywhere. (I honestly wouldn’t be that surprised to see a mule make it up a ladder.) If a mule takes against you, you are doomed. Give up now. Sell the thing, it’s the only way both of you will survive.

    And mules can kick you no matter where the heck you’re standing, too. They can kick sideways. They can kick their hind legs up past their chin. Seems like they can kick you if you’re on their back. Narrower bodies than horses, longer bodies than donkeys, damn flexible spines.

    And they can open slide latches with their lips.

    Have I ever mentioned that I *love* mules?

  6. #6 Luna_the_cat
    July 31, 2008

    Ben_Wraith: The way they smell.

  7. #7 BCham
    July 31, 2008

    To add to Luna_the_Cat: scientists have speculated that the MHC complex (a string of genetic data responsible for some immune responses) is responsible. These complexes produce molecules that apparently reflect the genetic diversity of the possessor and can be detected through smell. Claus Wedekind did a study with female college students and t-shirt smelling: women smelled tshirts that had been worn by men for 2 nights and had to determine which shirt was “more attractive”. The MHCs of both sexes were determined and in most cases, women found men with different MHCs from themselves more attractive. Kinda neat & makes you consider sniffing your date (though it would probably still be considered incredibly weird).

  8. #8 Blind Squirrel FCD
    July 31, 2008

    Ben_Wraith: Avoid cousins.

  9. #9 jfrancis
    August 1, 2008

    could we have missed the ‘let some air out of the (truck)tires’ obvious? horses and donkeys are way dumber so the
    offspring(mule) has a way better chance of being smarter.

  10. #10 John Jackson
    August 2, 2008

    The “hybrid vigor” article at:

    …doesn’t quite cover the idea that in domesticated breeds, traits of cunning and mental deviousness have been bred out somewhat. What the donkey may have lost might perhaps be covered by something the horse has retained, and vice versa.

    It would be interesting to know if mules are more canny than wild horses or asses (first catch yr “wild” equid!)

    “…marry somebody with an entirely different set of recessive[?] genes”!

    My parents tried. Maybe it didn’t work, maybe it did! (The “domesticated” argument doesn’t quite work with humans perhaps…or does it?)

  11. #11 David Baird
    August 10, 2008

    I’ve often speculated whether religions that stone their women and men to death for sexual and other misconducts weren’t acting to ‘domesticate’ the population.

  12. #12 John Jackson
    August 12, 2008

    David –

    A sinister and complicated thought! :-S

  13. #13 McFawn
    August 14, 2008

    Here the physical and mental merge. A donkey may be canny, but it is fairly small. A horse is large and powerful, but relatively easy to dominate–their size makes only a marginal difference in herd dynamics (i.e. a pony may be dominant over a draft horse). But a mule seems smarter because it is large and powerful with a better understanding of just what his or her large powerful body can do.

    Part of intelligence is the confidence to make a risky or nonstandard choice. For a donkey or horse, choosing the right bucket consistently might have been difficult because they were following a habitual pattern (say, right bucket first) or a standard alternating pattern. But the mule was more able to risk going hungry by acting on a hunch. What makes mules smarter is their ability to break out of patterned behavior. Iím sure you all know the old mule-handlerís saying: ďA good mule aint the same good mule he was yesterday.Ē

  14. #14 Magnetic Separator
    June 15, 2009

    They can kick their hind legs up past their chin. Seems like they can kick you if you’re on their back.

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