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I am not saying that gender variance in humans iscaused by morphs. But the existence of morphs among birds and mammals tells us that gender is not as clear cut and binary as many believe.
See also: http://www.crossdreamers.com/2009/12/transgender-animals.html
The sparrow with four sexes (on white-throated sparrow, Zonotrichia albicollis)
The mutation had flipped a large section of chromosome 2, leaving it unable to pair up with a partner and exchange genetic information. The more than 1,100 genes in the inversion were inherited together as part of a massive 'supergene' and eventually drove the evolution of two different 'morphs' — subtypes of the bird that are coloured differently, behave differently and mate only with the opposite morph. Tuttle and Gonser's leap was to show that this process is nearly identical to the early evolution of certain sex chromosomes, including the human X and Y. The researchers realized that they were effectively watching the bird evolve two sex chromosomes, on top of the two it already had.
“This bird acts like it has four sexes,” says Christopher Balakrishnan, an evolutionary biologist at East Carolina University in Greenville, North Carolina, who worked with Tuttle and Gonser. “One individual can only mate with one-quarter of the population. There are very few sexual systems with more than two sexes.” ...
The tan-striped birds are poor at singing, monogamous and fiercely protect their hatchlings from predators such as raccoons and snakes. The white-striped ones are aggressive, promiscuous, more cavalier about their offspring, and tuneful: Gonser says that they produce a more operatic refrain of oh-sweet-Canada. White-striped birds seem to mate only with tan-striped ones — a relatively unusual phenomenon called disassortative mating (see 'Opposites attract'). Tuttle became interested; why do the two morphs behave in this way?
Last Edited By: jackmolay Mar 7 17 12:24 AM. Edited 1 time