The sex of humans is controlled by the presence of X and Y sex chromosomes. On the other hand, many fish and reptiles' sexes are heavily influenced by the temperature of the eggs before hatching.
What would life be if human sex was influenced the same way?
Hotness and Coldness of Eggs Influence Sexes
It was first uncovered in 1966 by French zoologist Madeline Charnier from the University of Dakar that it was possible to control the sex of rainbow agama lizards using changes in temperature. She found that hatchlings from eggs incubated at higher temperatures turned out male, while those at a lower temperature were female.
Since then, researchers have uncovered other patterns of temperature-dependent sex determination.
Another example is observations made on the Hawaiian green sea turtle. Females incubated above a certain temperature were female, while eggs incubated at lower temperatures became male.
However, if the temperature fluctuates a mix of male and female hatchlings emerged according to a 2020 study published in the journal Bionatura.
Karla Moeller, a biologist from the Arizona State University explains that temperature controls sex determination in most turtles, many fish, all crocodilians, and some lizards.
Within a window of time during the embryonic development of various animals, the temperature can influence the production of sex hormones that can sway the fate of a hatchling.
Moeller notes that one cause for sex determination is the presence of an enzyme known as aromatase, which converts male sex hormones to female sex hormones. In many cases, such as the red-eared slider turtle, applied heat during the developmental stage can increase the presence of the enzyme and lead to more females.
Temperature-Dependent Sex Determination: An Evolutionary Mystery
Experts are uncertain why some species practice temperature-dependent sex determination, although a number of theories on the phenomenon exist.
Jennifer Graves, a geneticist from La Trobe University, Australia told Live Science, Öut best guess is that Temperature-dependent sex determination originated in reptiles that do not have parental care where the eggs are in close interaction with the environment.
Among reptiles, hatching eggs is often linked with the wet season where hatchlings are more likely to get more food. Diego Cortez, a biologist from the National Autonomous University of Mexico explains that elevated incubation temperatures are linked to the speed of embryonic development.
How Unlikely Can Temperature Determine the Sex of a Human Baby?
Unfortunately, all known temperature-dependent sex determination happens in species that are both egg-layers or oviparous, which means that their internal temperatures change with the environment. However, humans are not one of those species.
Cortez explains that this phenomenon is highly unlikely to happen to humans since it would require two temperatures for triggering either male or female, while the human body consistently maintains a body temperature of 37 degrees Celsius.
Despite the presence of some proteins that regulate circadian rhythms in humans, which are linked with temperature-dependent sex determination in reptiles, it can only sense a very small fluctuation in the internal temperature.
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