by Greg Mayer
The BBC reports on an abandoned cat with “three ears” found in Norfolk. Shelter staff at Feline Care Cat Rescue in East Harling have named him “Brian”*. [JAC: several readers also sent this to me.]
I can’t recall ever seeing such a cat, and neither could the shelter’s vet, though Jerry had apprised us of the existence of extra-eared cats a while ago. The first thing that struck me is that the cat does not have three ears, but rather three ear pinnae. Ears, in a strict sense, are the paired sensory organs at the back of a vertebrate’s head that detect vibration and movement. The pinnae are the external elaborations for directing sound waves to the ears proper that are found in most mammals. (And also in Vulcans, who are not mammals, but who are renowned for their pointed pinnae, which led to some suggestions for a Star Trek-themed name for Brian.) Most vertebrates have ears, but relatively few have pinnae. Some, such as lizards, just have holes in the sides of their heads (you can look through a lizard’s head from one side to the other by looking into its ear opening), while others, such as frogs, have the tympanum (eardrum) exposed on the surface.
The second thing that occurred to me is that the extra ear pinna is moving in the opposite direction from a famous trait studied by the great geneticist Sewall Wright— otocephaly. Meaning literally “ear head”, in this condition the ear pinnae expand and extend under the ventral side of the head (1-5), the lower jaw fails to develop, and, in extreme cases, the entire front of the head fails to develop as though squeezed in from the sides, the eyes touching (7), merging (to form a cyclops: 8-9), and finally disappearing altogether in the highest grade otocephalic individuals (10-12).
I had read and studied Wright’s paper on otocephaly as a graduate student, as I was interested in the genetics of traits of large phenotypic effect in vertebrates, and Wright had studied otocephaly and polydactylism (extra toes) in guinea pigs. Polydactylism is much more interesting, as changes in digit number have been important in vertebrate evolution, and some rodents also show an approach to hoof development, which is very important in mammalian evolution, and usually involves changes in digit number. Otocephaly, in contrast, has not led to any evolutionary novelties, but rather is lethal in most cases– Wright referred to otocephalic individuals as “monsters”. The late Will Provine, in his masterful scientific biography of Wright, discusses the significance of his work on guinea pigs for the development of Wright’s ideas on the importance of multifactorial inheritance and non-genetic factors. (I should record here my mourning of Provine’s passing this past September, which Jerry first alerted us to. His Origin of Theoretical Population Genetics, recommended to me when I was an undergraduate by then Stony Brook geneticist Dick Koehn, was my first real introduction to the history of science as a serious discipline, and influenced me greatly. I was much pleased when he occasionally joined the discussion on my posts here at WEIT.)
Although not important evolutionarily, otocephaly, which is known to occur in many mammals, had cultural significance, which Wright well knew. In his historical review of theories of the causation of otocephaly, he wrote the following passage, surely one of the most wonderfully erudite in all the literature of genetics:
We may pass rapidly over the theories of ancient times, according to which monsters were looked upon as the result of the play of the Gods, “ sports,” as signs of divine power or anger or as portents. The oldest known publication on the subject seems to be a brick found in ASHURBANIPAL’S library in Nineveh which gives in cuneiform the prognostication appropriate to each of a remarkable list of monsters…
[I should add that Ashubanipal’s name is in all caps because it is the style of the journal Genetics to capitalize the names of cited authorities in its papers: he’s probably one of the few Assyrian emperors cited as a reference in the scientific literature!]
Having checked up on the genetics of the merger and disappearance of the ear pinnae, I got back to our cat with an extra pinna, and turned to my bookshelf for my copy of Genetics for Cat Breeders. There, on page 168, I found the entry for “Four-ears”. It is inherited as a recessive, denominated dp, with affected cats suffering reduced fitness (as determined by a deficiency of affected cats in crosses). The head shape is peculiar, the lower jaw a bit underdeveloped (like low grade otocephaly!), and the affected cats’ behavior is lethargic, suggesting some brain abnormality (again, as found in otocephaly). The authority is Little (1957). So, Brian the cat is doubly odd: he has one extra ear pinna, not the usual two extra (when there are extras). I can’t see his right side in the photo, but I’ll take the BBC’s word that he’s oddly asymmetrical in his ear pinna numbers.
Sarah Hartwell‘s Messybeast Cats website has compiled a number of cases of four eared cats (and other ear anomalies) reported in the media, along with useful explanatory diagrams, and also interesting discussion and illustrations of a number of facets of cat biology (for example, color patterns). In her section on facial deformities, some of the cats pictured look like they are otocephalic. (Although many such enthusiast websites are, at best, unreliable, I have found Messybeast to be quite reliable, for example in its explanation of “winged cats” [I once had a winged cat myself!].)
Little, C.C. 1957. Four-ears, a recessive mutation in the cat. Journal of Heredity 48:57. (not seen; shockingly, the University of Wisconsin, Madison– the ‘public ivy’ research giant, not my home campus– does not have an electronic subscription to this well known, historically important, Oxford University Press, journal)
Provine, W.B. 1971. Origin of Theoretical Population Genetics.University of Chicago Press, Chicago.
Provine, W.B. 1986. Sewall Wright and Evolutionary Biology. University of Chicago Press, Chicago.
Robinson, R. 1971. Genetics for Cat Breeders. Pergamon Press, Oxford.
Wright, S. 1934. On the genetics of subnormal development of the head (otocephaly) in the guinea pig. Genetics 19: 471–505. pdf
*Maybe the Romans did this to him.
That’s all good and well, but does this one actually listen to you?
“(And also in Vulcans, who are not mammals,…”
What were those protuberances on female Vulcans’ chest for then? Sure looked like evidence of mammaries to my adolescent eyes.
A fascinating journey through some developmental quirks, all inspired by a 3-eared cat! I always find these sorts of things to be very informative since they give us insight into the ways that development normally happens.
The pinnae are formed along the margin of the 1st branchial arch, which is the arch that also makes the upper and lower jaw. This may be why if a defect expands the area that makes the pinnae, one sees a loss of jaw structures.
Anyway, mammal development is mediated by cell-cell interactions, and there are general principles that are applied over and over again in such embryos. One general principle is that structures form from a field of cells that are competent to form those structures. Assuming this applies to the 1st branchial arch, then, regional cell-cell interactions are likely involved in sorting out which cells make what parts. Once a group of cells decide they are going to make, say, a pinna, they would then send out an inhibitory signal to nearby cells that prevents nearby cells from also making a pinna. But if something happens to interfere with these inhibitory signals, one may see a duplication of the pinna. Perhaps this is what is behind the 3-eared cat.
Brian seems to have an underbite – perhaps his lower jaw is slightly underdeveloped.
Where does single toe(Hooflike) pig, called a mulefoot, fit in the evolution of mammals?
Huh. That is interesting. I did not know about those. From the looks of the feet it looks like two fused toes, rather than one larger toe. If right, then this resembles a condition called syndactyly.
Hmmmm
It seems that way on some but on others they stand up on the hoof just like mules and horses. I have some I breed, mine are mixed with standard breeds. Somewhere I read it was common in the standard breeds but they bred it out. In mine it seems to be a male dominant trait.