It is most fitting that our Class, Mammalia, is named for an aspect of the female reproductive tract. Especially with regards to the placental mammals (the Theria, which excludes platypuses, echidnas, and kangaroos), the challenges of mating have had a profound impact on our structure, function, and behavior.
Most mammals exhibit an estrous cycle. In this system, ovulation is accompanied by suite of physical and behavioral changes that indicate to males that the female is 'in heat,' or capable of conception. Business proceeds.
Humans are interesting because we have developed the menstrual cycle or 'permanent estrous.' Ovulation is outwardly concealed and conception is possible at any point in the cycle. The only external change is menstruation, the expulsion of an unfertilized ovum. Theoretically, the menstrual cycle evolved along with strong pair-bonding, as males who could not be sure when a female was in heat would be forced to monopolize one female for long periods of time to ensure his paternity.
Camels are also special, as they exhibit induced ovulation or the 'follicular wave.' Follicles are constantly growing and maturing, but ovulation is triggered only by the dirty deed itself. This unique cycle is the greatest obstacle to assisted fertility treatments in camels, for although the males are happy to contribute whenever the opportunity arises, females are quite picky about when they let their eggs out. The evolutionary implications of such as system will be covered in another post.
Most mammals exhibit an estrous cycle. In this system, ovulation is accompanied by suite of physical and behavioral changes that indicate to males that the female is 'in heat,' or capable of conception. Business proceeds.
Humans are interesting because we have developed the menstrual cycle or 'permanent estrous.' Ovulation is outwardly concealed and conception is possible at any point in the cycle. The only external change is menstruation, the expulsion of an unfertilized ovum. Theoretically, the menstrual cycle evolved along with strong pair-bonding, as males who could not be sure when a female was in heat would be forced to monopolize one female for long periods of time to ensure his paternity.
Camels are also special, as they exhibit induced ovulation or the 'follicular wave.' Follicles are constantly growing and maturing, but ovulation is triggered only by the dirty deed itself. This unique cycle is the greatest obstacle to assisted fertility treatments in camels, for although the males are happy to contribute whenever the opportunity arises, females are quite picky about when they let their eggs out. The evolutionary implications of such as system will be covered in another post.
Here, Dr. Vyas assesses follicle development:
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