Do you think human beings are made to mate at a certain time of year?
Throughout nature, we see seasonal breeding as part of species survival. Most animals are forced to mate in the summer-fall, in order to give birth in the spring.
Mating during late fall or winter would push birthing into summer, which would not allow ample time for the babies to develop and become self-sufficient enough to survive and thrive during a cold and long winter.
In the Arctic, many species are forced to mate within a one-week window in order to give offspring time to develop and prepare for winter!
Research by Dr. Russ Reiter suggests the hormone responsible for these mating cycles is melatonin. Melatonin is, of course, the master hormone produced in the pineal gland that regulates our connection to the light-dark seasonal or circadian cycles. During longer nights of winter, we produce more melatonin. The shorter nights of summer trigger less release of melatonin.1
The Pineal Gland + Melatonin for Seasonal Breeding
The only reliable indicator of the changing seasons is the number of hours between sunrise and sunset. For example, in June, you can have temperatures as high as 85° or as low as 25° in many parts of the US, but the number of hours between sunrise and sunset has been pretty much the same for millions of years.
The precision of these cycles is interpreted by the pineal gland through production of melatonin. Melatonin orchestrates the ebb and flow of our biological clocks, numerous hormones and in particular sex hormones that have ensured the survival of our species.
As the days begin lengthening in the spring-summer, melatonin levels are suppressed and reproductive hormone activity is increased. In winter, when nights are long, melatonin levels surge and reproductive hormone activity is suppressed.2,3 Increased winter melatonin is a natural means of contraception for many species, possibly including humans. In the 1990s, a melatonin birth control pill was under development.3
Since melatonin production is linked to light exposure, using melatonin as a birth control agent might be effective—as it was in traditional cultures, when sleep was initiated by sunset and activity by sunrise. However, it would be a pretty unpopular birth control pill, as the fine print may have to read, “Possibly only effective if sleep and total darkness is initiated just after sunset.”
In the end, The Dietary Supplement Health and Education Act of 1994 classified melatonin as a dietary supplement—thus, the development of melatonin as a birth control pill was squashed.
For millions of years, animals have synced up their breeding schedule with this predictable light-dark cycle. Melatonin is also responsible for changes to the color and thickness of the coats of animals and migration patterns.1
Dr. Reiter’s first studies evaluated hamsters. Hamsters’ testicles literally shrink during winter. In the spring, they swell to a considerably large size in proportion to their body. If hamster-sized testicles were on humans, they would weigh about eight pounds. This interesting characteristic makes the potential of testicular atrophy during winter extremely likely.1
Dr. Reiter and his associates discovered that the molecule involved in the shrinking or shriveling of the testicles each winter was melatonin. Increased of melatonin (linked to longer nights and long, cold winters) translated into an evolutionary trait that decreased sex drive and paused mating activities.1,2
In the 1890s, Eskimos were studied before exposure to the modern world and artificial light. In one of these cultures, during the long winter months with little or no light, women would completely stop menstruating. Their melatonin levels were also surging during these months. Come spring, when it was lighter for longer, melatonin levels would be suppressed, reproductive hormones would surge . . . and mating season would begin!5
In Northern Finland above the Arctic Circle, there is an eight-week period during summer where there is a significant surge in conception rates, and an associated boost in spring births. Researchers discovered that during this surge, there is a significant drop in melatonin levels.4
There is also a drop in melatonin production around the time of ovulation during a normal menstrual cycle. According to Dr. Russ Reiter, it is possible that this dip in melatonin production during ovulation is linked to increased fertility during that time.1,4 There is also a short surge in testosterone during ovulation to ensure an ample reproductive libido.
Our excessive exposure to artificial light after sunset has resulted in a disconnect to natural light-dark cycles. Many adult humans are producing less melatonin year-round than they normally should. This chronic melatonin deficiency is linked to a litany of health concerns and has become a new emerging branch of western medicine called, circadian medicine.
Premenstrual syndrome (PMS) symptoms such as headaches, weight gain, cravings, poor sleep, and irritability have all been linked to a decrease in melatonin production. Studies show that women with PMS produce less melatonin than other women, particularly a week before their cycle starts.1,6
Many experts believe humans were once seasonal breeders like all other mammals. As artificial light was first introduced in the form of fire, humans stayed up longer into the night, slowly altering the natural circadian production of melatonin and other sex hormones.
Soon, the long nights of winter that suppressed conception rates were replaced with more artificial light, resulting in less sex-hormone suppression. It seems that over thousands of years, we traded our seasonal breeding instincts to be able to breed year-round, as we do today.
That said, there are still significantly higher birth rates in the spring in the colder climates compared to any other time of year.4,5
What do you think . . . a coincidence? We would love to hear your thoughts!