It's the pelvic thrusts...
Nature reported yesterday on Kimchi et al's (2007) work with Trpc2-/- mice, which suggests that male behavior patterns are inhibited in female mice by smell. The mice were a strain developed to lack the Trpc2 gene, which activates the vomeronasal organ in mice, responsible for the detection of pheromones. Female mice lacking this gene failed to exhibit female-specific behaviors (such as nursing) and did exhibit male-specific behaviors, such as mounting. Kimchi et al point out that the mounting behavior demonstrated by the knockout mice was different from normal female mounting behavior: 30-40% of normal female mice mounted intruders as a dominance display (compared to over 80% of male and knockout female mice). Mounting time and number of pelvic thrusts by knockout females were also "statistically indistinguishable" from male mice.
Kimchi et al report that removing the vomeronasal organ surgically had the same effect. However, Kelliher et al (2006) found pheromone recognition was not dependent on Trpc2, although the vomeronasal organ was required. In contradiction, Leypold et al (2002) reported that male and female mice missing this gene were not aggressive to intruders (the opposite of Kimchi's results) but that males attempted to mount both males and females. (see Keverne's 2005 review for more on the vomeronasal organ's role in reproductive behavior.)
Of course, humans don't have a vomeronasal organ, although the debate about human pheromones appears to be never-ending. Generalizing these results to humans would be foolish and useless: so let's try. Despite being a long-time smoker, I do relate to the world very much by sense of smell. Some of this reaction is conscious, some of it is barely conscious, and I suspect there's a large component of smell involved in my unconscious like or dislike of new people. I've discussed this phenomenon with men and women, smokers and non-smokers, and the distribution of people who are aware of an olfactory component to their social interactions doesn't seem to divide along any of these lines. I can't say I noticed a change in my sense of smell during my transition, but I sure noticed a change in my own scent -- a commonly reported side effect of testosterone. I don't think I smell like a man or a woman anymore, but I can't exactly go around sniffing transsexuals to see if we share a common scent.
Kimchi et al report that removing the vomeronasal organ surgically had the same effect. However, Kelliher et al (2006) found pheromone recognition was not dependent on Trpc2, although the vomeronasal organ was required. In contradiction, Leypold et al (2002) reported that male and female mice missing this gene were not aggressive to intruders (the opposite of Kimchi's results) but that males attempted to mount both males and females. (see Keverne's 2005 review for more on the vomeronasal organ's role in reproductive behavior.)
Of course, humans don't have a vomeronasal organ, although the debate about human pheromones appears to be never-ending. Generalizing these results to humans would be foolish and useless: so let's try. Despite being a long-time smoker, I do relate to the world very much by sense of smell. Some of this reaction is conscious, some of it is barely conscious, and I suspect there's a large component of smell involved in my unconscious like or dislike of new people. I've discussed this phenomenon with men and women, smokers and non-smokers, and the distribution of people who are aware of an olfactory component to their social interactions doesn't seem to divide along any of these lines. I can't say I noticed a change in my sense of smell during my transition, but I sure noticed a change in my own scent -- a commonly reported side effect of testosterone. I don't think I smell like a man or a woman anymore, but I can't exactly go around sniffing transsexuals to see if we share a common scent.