The series “Imaginary Earths” reflects how the world can be if one important aspect of life changes, whether it is related to the planet or humanity.
The gender of humans is largely controlled by the X and Y genders chromosome. In many reptiles and fish, however, sex is affected by how hot or cool eggs are before they hatch. How can life be for people if sex is also below the temperature of the world?
The fact that it was even possible to control the sex of animals with heat or cold was first exposed in the rainbow agama lizard in 1966 by the French zoologist Madeline Charnier at the University of Dakar in Senegal. She found that hatches of eggs incubated at lower temperatures were female, while those that developed at higher temperatures were male.
Since then, scientists have discovered other patterns of temperature-dependent sex determination. For example, with the Hawaiian Green Sea Turtle, women occur when it is incubated above a certain temperature, and men when it is below a certain temperature, and when the temperature in nests varies between the extremes, a mixture of men and women is seen, according to a study from 2020 published in the magazine. Bionatura. In contrast, with the American crocodilefemales develop from the extreme of hot and cold and males of medium temperatures.
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Temperature control sex determination crocodiles, the most turtles, many fish and some lizards, according to organic biologist Karla Moeller at Arizona State University. Within a specific time period during the embryonic development of these animals, heat or cold can affect the production of sex hormones, which in turn can affect the fate of a hatchery.
Moeller noted that one cause of temperature-dependent sex determination is an enzyme known as aromatase that can convert male sex hormones into female sex hormones. In animals such as the red-eared turtle, heat during a particular stage of development can increase the levels of this enzyme, leading to more females.
Evolutionary mysteries
It remains uncertain exactly why these animals practice temperature-dependent sex determination, although a large number of theories exist, Jennifer Graves, a geneticist at La Trobe University in Melbourne, Australia, said in a telephone interview with Live Science.
“Our best guess is that temperature-dependent sexing originated because reptiles do not have parental care and the eggs are in close interaction with the environment,” Diego Cortez, a biologist at the National Autonomous University of Mexico in Mexico City, told Live Science said. in an email. “We also know that increased incubation temperatures accelerate the development of embryos. The sex associated with higher incubation temperatures will therefore hatch earlier.”
Since breeding in reptiles is often associated with the rainy season, when life is in full swing, any breeding that emerges early is likely to get more food, Cortez said. “With more food, it will grow faster and have a better chance of surviving until it reaches maturity,” he said.
According to this idea, known as the hypothesis of survival to adulthood, “if for some reason it is better for a species to have larger females or larger males at adulthood, this sex will be linked to high incubation temperatures so that it can hatch earlier in the season, ”said Cortez.
Another possibility is that the temperature-dependent sex determination mothers can control the sex of their offspring. “Scientists have suggested that female alligators may choose cooler nests to have more female nesting sites, so if the population is low, a female can lower their nests near the water, allowing more females to hatch,” Graves said. In contrast, when populations have reached a stable level, females choose warmer nests “, so there are many more males that get more male aggression and competition.” The next generation of women could then choose from the best men, Graves suggested.
Unlikely in humans?
All known species with a temperature-dependent sex determination are both oviparous, or egg layers, and cold-blooded, meaning that their body temperature changes with that of their environment. However, people are not one of those things.
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As such, “temperature-dependent sex determination in humans is not very likely because you need at least two different body temperatures – one that will cause female development and one that will cause male development,” Cortez said. “But the human body is always at 37 degrees Celsius (98.6 degrees Fahrenheit).”
Yet, if women could somehow experience a range of body temperatures, Cortez said he could suggest a way for temperature-dependent sex determination in humans. He noted that some proteins help regulate circadian rhythms in humans – our internal watches – is also linked to temperature-dependent sex determination in reptiles. These proteins, known as CLK kinases, are found throughout the body and can detect very small fluctuations in body temperature.
“It would not be impossible to think that if CLK kinases are involved in temperature-dependent sex determination in reptiles, where they observe large changes in incubation temperatures – usually between 3 and 7 degrees Celsius [5.4 to 12.6 degrees F] ‘that the system can be adapted to address smaller temperature changes that hypothetically can then be linked to the sex of the embryo,’ Cortez said.
To prevent temperature-dependent gender determination in humans, Graves suggested that one possibility is that we somehow become poikilothermic – that is, we cannot control body temperature – just like the naked mole rat. Another possibility is that we somehow had to lay eggs like ‘after platypus, she added.
Control of sex
So what can mankind look like if temperature can determine the sex of our offspring? The most important consequence would probably be that it would then be trivial for parents to determine their children’s gender, Graves said.
One major risk is the potential for major gender imbalances in a society.
“A lot of people like to determine the gender of their children,” Cortez said. “Unfortunately, the preferred sex in many places on this planet is men. So if humans could decide the sex of their offspring with a non-complicated technique, such as changing their body temperature during a specific week during pregnancy – the incubation temperature would have to is only changed during the week when sex is determined – I am confident that it will create many societies that are biased towards men. ‘
That would be a problem.
“We know that the excess of one specific gender in adult populations creates an unbalanced population linked to increased violence, more sexual conflict, because it is not easy for one gender to get a partner, less parental care, and so on, “Cortez added. . “So, in other words, a less harmonious society.”
One can imagine that governments can intervene to ensure that one generation is not favored too much. But, “we can then begin to speculate what might happen if the choice of sex did not belong to parents – what forces could interest the state in skewing the gender relationship in some way,” Graves said.
Originally published on Live Science.