Dear Matthew: My friend tells me that he read that scientists can figure out from somebody's spit whether or not a person is likely to be a criminal when they grow up. I think he's got some of his facts confused. How can this be? What can spit tell you about somebody? — Need New Friends, El Cajon

I’ve been long convinced that there is absolutely no subject so obscure, revolting, boring, or pointless that someone, somewhere isn’t studying it. And more than likely, with a federal grant. Case in point: spit. The Einstein of expectoration: James Dabbs, Georgia State University psychologist. (Funding source: National Science Foundation.) Dabbs is poking around in saliva to determine individual testosterone levels, with hopes, apparently, of shedding some light on the effects of sex hormones on personality. Hormone levels gauged from saliva are as reliable as those from blood, and it’s easier to get volunteers to spit than to bleed for you, apparently. To hear him tell it, his students have hardly any trouble getting total strangers accosted on the street to spit into a little cup for them, which to me is more amazing than any conclusions he’s reached so far from his studies.

To date, Dabbs has about 3000 samples from the general population of men and women, plus some selected populations, such as ministers and violent criminal inmates. In general, so far, his analyses show higher than normal testosterone levels among some salesmen, lawyers, prisoners, and people with no jobs at all. But he doesn’t necessarily find high levels in Type A-personality executives or others who are driven to achieve. High testosterone levels seem more clearly related to physical violence than to more benign types of aggressiveness. Even violent female inmates have testosterone levels elevated above the average for other females. (Testosterone is produced in small quantities by women’s adrenal glands.) The low-end testosterone crowd, from Dabbs’s experience, includes ministers and farmers.

Dabbs doesn’t yet claim that a spit test will predict behavior, so your friend was taking more than a few liberties with the data. It’s all just fact-gathering at this point. Adding pieces to the big puzzle of why we human beings act as we do.