Mind blown. I just discovered that data I collected one afternoon during my junior year of college is important and useful, now. I was sitting at the banquet of the annual SBN conference, when former president of the society, Art Arnold, said “Hey, that paper you published 30 some years ago has been so useful in getting researchers to start paying attention to sex differences.” At first I was confused. Was he talking about that old review article I co-authored with my postdoctoral mentor (which keeps getting cited even though we’ve both written much better reviews)? Or maybe he meant the overrated article we published in Science in 1989? No, it turned out he was excited about a paper that emerged from a side project loosely related to my FSU undergraduate honors thesis in which I measured the length of mouse taints.
It all started when some grad students and a postdoc decided they wanted to give the googly-eyed, work-study student (me) a “discovery experience.” This, by the way, is the essence of mentoring, and I am forever grateful to those guys. They gave me 50 or so one-day-old mouse pups and said “Figure out which ones are male and which are female; collect some data; and show us how to document the sex difference.” I sat alone in the room, like the miller’s daughter in Rumplestiltskin, staring hopelessly at the seemingly identical embryonic bodies (see pic). I focused on the place where you might expect to see a tiny penis, but where I hoped to see a penis, there was only a small bump and a small hole behind the bump. Each and every mouse had the same bump-and-hole arrangement. Finally, after more staring, I noticed that the bump-to-hole distance was small in some mice and large in others. The hoity toity science name for this is the “anogenital distance.” To the likes of me, the term for this distance is the taint, because it tain’t the genital and it tain’t the other thing. So, I divided the pups into two piles, a short-taint pile and long-taint pile. Now how was the miller’s daughter going to spin mouse taint into scientific gold? My Rumplestiltskin was a professor who studied the visual system, the late Howard Baker. I told him I was trying to measure a very tiny distance that I could barely see with my naked eye. He gave me a reticle, a glass eyepiece for a microscope with a ruler engraved on the lens, which allows measurements accurate to 0.01 mm. I measured all the little mouse taints, and found the mean for each group. I did a t-test, and the difference was highly significant. I guessed that the those mice with the smaller taints were the females. Correct! Chuck and John, the grad students and postdoc in the lab already knew the answer, but since I discovered it without any help, they encouraged me to publish a paper. Hence the 1978 publication in Behavioral Research Methods and Instrumentation, “Determining the sex of neonatal mice, Mus musculus.“
Howard Baker never demanded my first-born son, few colleagues since have been so generous regarding authorship, and I rarely think of this one-page publication in a minor journal. Half the time I don’t even list it on my c.v. I just assumed in 1978 that everyone knew the importance of knowing the sex of your experimental animals on the day of birth. Tragically, the majority of scientists stubbornly refuse to look at both sexes in their experiments. The fact is, males and females differ in response to pain, drugs, hormones, and their propensity for many different diseases. Sex hormones have profound effects during early development, both pre- and neonatally, and these hormones masculinize or feminize the individual, determining their adult response to drugs, cancer, infections, pain, diet and exercise. We now have a large body of data on common diseases and biological processes; most of it on males by a ratio of 5:1. In 1993, the importance of sex differences and of early hormonal effects prompted the NIH to mandate the enrollment of women in human clinical trials. This mandate should also apply to the animal research on which the human research is based. Excuses for the male-only bias include “females are too variable due to their estrous cycles,” and even more ridiculous, “I don’t know how to tell the difference between the sexes.” It taint rocket science; even a work-study student at a state school could figure it out.