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October 28, 2007

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Humans go into heat after all, strip club study finds

Oct. 28, 2007
World Science staff

Mam­mals go in­to heat. Ex­cept for hu­mans, of course—it’s just for an­i­mals. Right? 

That con­ven­tion­al wis­dom seems to be wrong, a group of re­search­ers has found. 

The sci­en­tists col­lect­ed ev­i­dence from some lo­cales where sex­u­al heat is most reg­u­larly on dis­play, strip clubs. And they meas­ured it with a tool that rarely lies in gaug­ing the val­ue peo­ple place on things: mon­ey.

Heat, or es­trus, is a reg­u­larly re­cur­ring time pe­ri­od dur­ing which fe­males are most sex­u­ally re­cep­tive and at­trac­tive to males, cor­re­spond­ing with the time at which they’re most ca­pa­ble of con­ceiv­ing. Hu­man fe­males have no ob­vi­ous es­trus, lead­ing to bi­ol­o­gists’ tra­di­tion­al as­sump­tion that it was lost dur­ing hu­man ev­o­lu­tion.

But in a study published the Oct. 27 is­sue of the re­search jour­nal Ev­o­lu­tion and Hu­man Be­hav­ior, the in­ves­ti­ga­tors found that such a cy­cle does con­tin­ue in us. 

Surveying strip-club lap dancers, who pe­r­form erot­ic dances for for cash, they found that tips vary by an aver­age of 45 pe­r­cent de­pend­ing on the time of the month, cor­re­spond­ing to the length of the ovu­la­tory cy­cle. That’s the one-month cy­cle in which a ripe egg is re­leased from the ovary, be­com­ing avail­a­ble for fer­til­iz­a­tion.

Dur­ing peak times of the cy­cle lap dancers made $335 per five-hour shift on av­er­age, com­pared to $260 dur­ing typ­i­cal pe­ri­ods, the re­search­ers found. Dur­ing men­strua­t­ion, the wom­en made only $185 on av­er­age. The peak earn­ings dur­ing a cru­cial phase of the cy­cle could only lead to one con­clu­sion: fe­males were in heat, the in­ves­ti­ga­tors said.

“These re­sults con­sti­tute the first di­rect eco­nom­ic ev­i­dence for the ex­ist­ence and im­por­tance of es­trus in con­tem­po­rary hu­man fe­males, in a real-world work set­ting,” wrote the re­search­ers, Geof­frey Mill­er of the Un­ivers­ity of New Mex­i­co and col­leagues. By com­par­i­son, they found, dancers us­ing con­tra­cep­tive pills, which sup­press ovula­t­ion, showed no earn­ings peak.

The team col­lect­ed its in­forma­t­ion through a web­site where 18 dancers recorded their men­strual pe­ri­ods, work shifts, and tip earn­ings for 60 days—a to­tal of 5,300 “lap dances.”

* * *

Mammals go into heat. Except for humans, of course—it’s just for animals. Right? That conventional wisdom is wrong, a group of researchers has found. The scientists collected evidence from some locales where sexual heat is most blatantly and regularly on display, strip clubs. And they measured it with a tool that rarely lies in gauging the value people place on things: money. Estrus, or heat, is a regularly recurring time period during which females are most sexually receptive and attractive to males, corresponding with the time at which they’re most capable of conceiving. Human females have no obvious estrus, leading to biologists’ traditional assumption that it was lost during human evolution. But in the Oct. 27 issue of the research journal Evolution and Human Behavior, researchers found that such a cycle does continue in us. Studying strip-club lap dancers, who perform erotic dances for for cash, the researchers found that tips vary by as much as 45 percent depending on the time of the month, corresponding to the length of the ovulatory cycle. The ovulatory cycle is the one-month cycle in which a ripe egg is released from the ovary, becoming available for fertilization by sperm. During peak times of the cycle lap dancers made $335 per five-hour shift on average, compared to $260 durying typical periods, the researchers found. During menstruation, the women made only $185 on average. The peak earnings during a crucial phase of the ovulatory cycle could only lead to one conclusion: females were in heat, the investigators said. “These results constitute the first direct economic evidence for the existence and importance of estrus [heat] in contemporary human females, in a real-world work setting,” wrote the researchers, Geoffrey Miller of the University of New Mexico and colleagues. By comparison, they found, dancers using contraceptive pills, which suppress ovulation, showed no earnings peak. The team collected its information through a website where 18 dancers recorded their menstrual periods, work shifts, and tip earnings for 60 days—a total of 5,300 “lap dances.”