|In 2007, American evolutionary psychologist Geoffrey Miller, in a study of eighteen strippers who worked 296 shifts, representing about 5,300 lap dances, over the course of 60-days (two-cycles), found that those "in heat" (ovulating) earned twice as much as those menstruating.|
In this sense, an entity being "in heat", referring to heat as in sexual drive, models a reactive human molecule on the analogy of a hot gas-phase particle in energetic movement in need sexual chemical reaction (atomic exchange). 
A recent 2007 study, led by American evolutionary psychologist Geoffrey Miller, of the income of eighteen strippers who worked 296 shifts, representing about 5,300 lap dances, over the course of 60-days (two-cycles) showed that normal cycling participants earned about $335 per shift while in heat or in estrus, compared to $260 in luteal phase and $185 in menstrual phase, in a typical five-hour shift; the results of which are as follows: 
1. in heat (definition) – Sexual Dictionary, Sex-Lexis.com.
2. (a) Thims, Libb. (2007). Human Chemistry (Volume One), (preview). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (preview). Morrisville, NC: LuLu.
3. (a) Miller, Geoffrey, Tybur, Joshua M., and Jordan, Brent D. (2007). “Ovulatory Cycle effects on Tip Earnings by Lap Dancers: Economic Evidence for Human Estrus” Evolution and Human Behavior, 28: 375-381.
(b) Geoffrey Miller (psychologist) – Wikipedia.