Five news items about sex and development

The Complex Issues of Gender Which of our characteristics has a greater impact on our lives than gender? What would remain of the world as we know it without intergender relationships and gender roles? Members of most species on Earth belong to one sex or the other. This division is a very “costly” adaptation. Its price is not only a waste of energy but also a reduction in the number of individuals directly producing offspring. This is offset by the acceleration of evolution. For the developmental control program to adapt to a changing world, it must receive information about its demands. The primary way to obtain such information is to allow only those individuals whose life course has proven successful to participate in reproduction. The more rigorous the selection, the more effectively this channel for transmitting information about environmental demands works. Thanks to sexual dimorphism, the male sex can be subjected to more intense selection. Even if most males perish, this will not affect the population’s reproductive potential; however, the next generation will consist of individuals suited to the environment’s demands. The phenomenon of sex has likely arisen many times in evolution, and the organisms inhabiting our planet have tried various mechanisms for determining it. Recently, several news items have emerged regarding this issue. The role of genes that trigger male development may involve altering hormonal levels. Hormones are regulators that enter the internal environment. This works well if that environment is reliably isolated. However, in aquatic organisms, the boundary between the external and internal environments is not very robust. Fish are particularly unlucky: the land is populated by their numerous descendants, which release regulatory substances inherited from their ancestors into the environment. American researchers studied the development of bass and chukuchan (these are types of fish!) and observed widespread feminization of their males. Female sex hormones entering the water from cattle and humans—and especially from women taking hormonal contraceptives—disrupt the normal development of fish. 42% of male bass in the Potomac River, on which Washington, D.C., is situated, turned out to be hermaphrodites. Male chukuchan do not produce eggs, but they also exhibit various reproductive abnormalities. However, in some cases, sexual plasticity can be beneficial. Australian researchers studied the development of the gobiodon, a sedentary coral reef fish. For this species, finding a suitable mate in a diverse and dangerous environment is a major challenge. As it turned out, a partial solution was the ability of gobiodons to determine their sex only after encountering a suitable conspecific. Young fish are sexless; when they encounter a female, they become male, and when they encounter a male, they become female. A solitary fish, however, never matures. When Sex Is No Fun A joint French-American research team recently published the results of a study on the population dynamics of viviparous lizards in small populations with varying ratios of females to males. The result was unexpected. It is clear that reproductive potential (the possible number of offspring) in populations is determined exclusively by the number of females. But suppose we compare small populations with equal numbers of females. How does the number of males affect their chances of survival? When there are very few males, their scarcity will prevent all females of reproductive age from leaving offspring. However, such a situation is rare, since the disparity in numbers is usually not significant (and one male can handle several females). On the other hand, an excess of males leads to increased female mortality and thus reduces the population’s chances of survival. Mating in viviparous lizards is quite rough: the male holds the female with his jaws and claws. Surviving females in groups with an excess of males have significantly more injuries. Strangely enough, to preserve such a population, it is advisable to remove the excess males! Populations with an excess of males can arise as a result of changes in living conditions. If, for example, male mortality decreases due to global warming, their excessive sexual enthusiasm could become a detrimental factor. Interestingly, there are never too many females: a large number of them simply means that competition among the offspring will be fiercer, and only the truly highly adapted individuals will emerge victorious. But with males, things can go too far. Who would have doubted it… Early-maturing children René Descartes believed that the pineal gland is the point of connection between the spirit and the body, since it is one of the few unpaired structures that are well-developed in humans and located at the base of the brain. Among other things, this part of the endocrine system is responsible for the phenomenon of photoperiodism—the regulation of the life cycle depending on the length of daylight hours. For our ancestors, small animals living in a seasonal climate, photoperiodic regulation of reproduction was very useful. In order for offspring to be born “well-fed” in the summer, they had to be conceived in the spring, as the days began to lengthen. Humans have long since switched to off-season reproduction; the duration of pregnancy in female Homo sapiens has increased dramatically, yet the old physiological regulatory mechanism has persisted, albeit in a vestigial form. The fact, known to every poet, that people fall in love more often in the spring is precisely linked to the increase in the concentration of sex hormones in the blood in response to the lengthening of daylight hours. In humans living in darkness (as in other vertebrates), the pineal gland produces the hormone melatonin. A decrease in melatonin triggers a chain of events leading, in particular, to an intensification of sex hormone synthesis. For a person living in conditions close to natural ones, such a regulatory system does not pose any particular problems. Unfortunately, it can be activated as a result of anthropogenic changes to the environment. Thus, one of the likely causes of the phenomenon of acceleration (the acceleration of maturation and increase in body size among the populations of civilized countries beginning in the second half of the 20th century) is the widespread use of artificial lighting. In this regard, a finding by scientists at the University of Florence (Italy) is alarming: they discovered that children’s television viewing suppresses melatonin production. The study involved children aged six to twelve who spent about three hours a day watching TV, playing computer games, and playing video games. When the young children were deprived of their favorite pastime for a week, their blood melatonin levels rose by 30%. As other studies have shown, boys and girls who spend a lot of time on video games and television begin sexual activity earlier and weigh more than their more conservative peers. All these changes may be the result of a disruption in regulation within the organ “where the spirit is connected to the body.” Early is not always better, after all; there is a price to pay for acceleration. Just compare the taste of early-ripening and regular apple varieties… Oh, you crooked face! In recent years, thanks in no small part to the work of researchers at the Institute of Developmental Biology of the Russian Academy of Sciences, a method for studying the fluctuating asymmetry of various organisms to assess their developmental conditions has gained popularity. The basic idea behind the method is this: the less favorable the conditions in which an organism develops, the greater the chance that its control systems will be unable to ensure normal development. When examining any organism, we seem to observe a single outcome of development and cannot assess the probability of others. However, in some cases, we have two relatively independent results—the outcomes of development of the right and left sides of the body in mirror-symmetrical organisms. The greater the difference between them, the higher the uncertainty of development. It typically increases under unfavorable environmental conditions, as well as in genetically unbalanced (e.g., hybrid) organisms. Naturally, only fluctuating asymmetry, whose values are randomly distributed around zero, is suitable for studying such phenomena. For example, when studying humans, one should not use traits related to the asymmetry of the dominant and non-dominant hands or to the asymmetry of the brain hemispheres. The greater development of the right hand in right-handed people is the result of functional, not fluctuating, asymmetry, and is not related to developmental instability. However, the patterns on the fingertips or the iris of the eye are much more interesting in this regard… In a recent study conducted at Ohio University, researchers investigated the link between asymmetry in the ears and fingers, on the one hand, and a person’s aggressiveness, on the other. Students were put in an awkward situation during a phone call, and then the force with which they slammed the receiver down on the phone was measured. “Asymmetrical” people turned out to be noticeably more aggressive. Overall, the result was expected. But this is only the first step on a very promising path. It is interesting to wonder whether biometric information collected for the purpose of identifying a person can be used to probabilistically assess their character. A father is not just about genes It has long been known that developing individuals are influenced by non-genetic regulators transmitted through the egg cell. For example, whether a snail’s shell spirals clockwise or counterclockwise depends on the polarity of the egg cell, which is determined while the egg is still in the ovaries of the mother (a hermaphroditic individual). The influence of certain factors on the egg cell can cause changes that will manifest in the adult individual. In humans, an interesting phenomenon is associated with this. Egg cells (from which future children will develop) are formed in a woman during her embryonic development. It turns out that exposure to certain factors during pregnancy can affect the egg cells formed by the developing embryo, and the changes will only manifest in her grandchildren! In these and other known cases, non-DNA-related information is transmitted through the egg cell. Sperm, as it had previously been thought, is so economically designed that it cannot accommodate additional information—it is optimized for transporting DNA in a very compact form. However, recent studies conducted in England and the United States have shown that the sperm cell transmits at least six types of messenger RNA molecules, and perhaps some other regulators as well. These substances activate the developmental program necessary for the early stages of development, which is contained within the egg cell itself. The biologists’ discovery is being discussed primarily because it may explain the difficulties encountered in cloning mammals. Perhaps it is precisely these regulators that are missing for the development of the egg cell, into which a new nucleus is simply inserted during cloning. On the other hand, a new argument has emerged for proponents of the epigenetic theory, who insist that development is not merely the realization of a hereditary program, but the emergence of a unique entity through the interaction of a multitude of factors of various natures. D. Shabanov. The Difficult Problems of Sex // Computerra, Moscow, 2004. – No. 46 (570). – pp. 17–19 D. Shabanov. When Sex Is No Joy // Computerra, Moscow, 2006. – No. 13 (633) D. Shabanov. Early-Maturing Children // Computerra, Moscow, 2004. – No. 29–30 (553–554). – p. 14 D. Shabanov. Oh, you crooked face! // Computerra, Moscow, 2004. – No. 34 (558). – p. 18 D. Shabanov. A Father Is Not Just About Genes // Computerra, Moscow, 2004. – No. 21 (545). – pp. 15–16