Editing Animal sexual behaviour (section)

===Sheep===
An October [[2003]], [http://endo.endojournals.org/cgi/content/abstract/145/2/478 study] by Dr. Charles E. Roselli et al. ([[Oregon Health & Science University]]) states that homosexuality in male sheep (found in eight percent of rams) is associated with a region in the rams' brains which the authors call the "[[ovine Sexually Dimorphic Nucleus]]" (oSDN) which is half the size of the corresponding region in other male sheep.

However, some view this study to be flawed in that the determination of homosexuality within the sheep, (sample population of twenty-seven for the study), was to have animals who were unable to mount female ewes placed in a cage with two stanchioned males and two unstanchioned females (that is, the males could not move or struggle while the females could). Given the aggressive nature of the sheep copulation, the uneven treatment of males and females, many see this as simply evidence that the sheep in question were unable to be aggressive enough to mount females. Some say that the results were situational sexuality, unlike the bonds seen in human homosexuality.

The scientists found that, "The oSDN in rams that preferred females was significantly larger and contained more [[neurons]] than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of [[aromatase]], a substance that converts [[testosterone]] to [[estradiol]], an [[estrogen]] [[hormone]] believed to facilitate typical male sexual behaviours. [[Aromatase]] expression was no different between male-oriented rams and ewes."

"The dense cluster of neurons that comprise the oSDN express [[cytochrome P450]] aromatase. Aromatase mRNA levels in the oSDN were significantly greater in female-oriented rams than in ewes, whereas male-oriented rams exhibited intermediate levels of expression." These results suggest that "...naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and its capacity for estrogen synthesis."<ref>[http://endo.endojournals.org/cgi/content/abstract/145/2/478 The Volume of a Sexually Dimorphic Nucleus in the Ovine Medial Preoptic Area/Anterior Hypothalamus Varies with Sexual Partner Preference - Roselli et al. 145 (2): 478 - Endocr...<!-- Bot generated title -->]</ref> As noted previously, given the potential unagressiveness of the male population in question, the differing aromatase levels may also have been evidence of aggression levels, not sexuality. The results of this study have not been confirmed by others.