Interview with zoologist and evolutionary biologist Axel Meyer published on July 20, 2022 in the Frankfurter Allgemeine Zeitung (Am Ende kommen immer Männchen und Weibchen heraus)

Biology and the Gender Debate:
In the end, we always find males and females.

What can we learn about sex and gender in humans from the sex distribution in animals and plants? This is what evolutionary biologist Axel Meyer explains in an interview.

Mr. Meyer, you are a zoologist and evolutionary biologist and have published numerous books and articles on the biology of sex differences. Currently, there is a cultural war raging over the question of the number of sexes. How are the concepts of "sex" and "gender" treated in biology?

Two articles by biological theorist David Haig come to mind. He once surveyed the English-language literature of the natural, social, and cultural sciences to see how often these two terms were used. The word " gender " appeared as early as the mid-1950th century, but since the 1960s and XNUMXs, the two words have increasingly been used synonymously. Historically, the difference lies in the fact that the word "sex" does not only designate the act or reproduction, but rather distinguishes the two sexes, male and female, from a biological point of view. The boundaries are blurring today, but for fish, for example, we would never speak of "gender", but of "sex".

About fish, there are species that can change sex, for example from female to male or vice versa. How do they fit into a binary system?

We know this for example for clownfish, famous since Nemo, or for some lippard fish. If you like, cultural or ecological circumstances take care of that, because it depends on how easy it is to find a female or a male. Yes, so there are organisms that can change "sex" but not "gender", and that can perhaps produce female gametes first and then males. These rare exceptions, however, have nothing to do with the conceptual difference between sex and gender.

Another word was used in the context of a conference – initially cancelled - at Humboldt University (see article The fanatics achieve their goal) : gametes, by which we mean germ cells. To what extent are they decisive?

Because the relative size of the gametes is the criterion for defining the animal that we call female or male. This is called anisogamy, the inequality of the gametes. And it is the cause of many of the differences between males and females, which Darwin described in his second book on sexual selection.

Does this mean that the largest gamete makes the living being responsible for it the mother, and the smaller ones make the father?

Exactly, and this has many implications. Almost universally, the variance in reproductive success is much greater among males of a species than among females. Take elephant seals, for example, with their " beach masters ", which dominate a part of the beach - and fertilize all the females that land there. A single male can become the father of a hundred or more young, while the vast majority of other males remain without offspring, perhaps for their entire lives.

The competition of a sex - most often the male gender - to gain favor with others is considered a driving force of evolution, but it requires considerable effort. If it is just a matter of exchanging genetic material, bacteria can do this too, and relatively more easily. Why is it so complicated?

This is a fascinating question that is difficult to answer. There is also talk that sexual reproduction doubles the cost of reproduction, because it now takes two individuals of the same species to produce offspring. If asexual reproduction took place, each individual could reproduce. There are different ideas and hypotheses about why sex still emerged in evolution, even multiple times, from initial isogamous reproduction. An important argument in this sense is that the production of haploid gametes (by a special cell division mechanism called meiosis), which contain only one set of chromosomes as in the case of eggs and sperm, allows recombination to occur. The new genetic variation is probably the decisive advantage of sexual reproduction.

Why would this be advantageous? Here too, there are many hypotheses. Better defense against diseases and parasites is often mentioned; a typical argument against this is that some animals can alternate between sexual and asexual reproduction.

There are also rare exceptions, including the viviparous toothed carp of Central America. Females can reproduce on their own, but they need copulation and sperm from males of other species to be stimulated, but not to be fertilized. The timing of this "return" is a matter of debate. It may be related to the fact that their environment is predictable, variance through sexual reproduction is not necessary. The genetic mechanisms of sex determination are surprisingly variable, but for mammals it is the combination of the two sex chromosomes X and Y that is decisive, for birds for example W and Z. In some evolutionary lines things have evolved very differently, in many reptiles it is the temperature in the spawning area that determines sex, even in fish it is very variable. Most of them do not have a sex chromosome, but have corresponding regions and genes, spread over several chromosomes.

Sex chromosomes, which originally developed from normal chromosomes, are also said to be a luxury of evolution.

That's what they could be called. There are several hypotheses about why sex chromosomes developed from autosomes. One peculiarity of sex chromosomes is that recombination does not take place precisely because there is no second chromosome, as in the case of the Y chromosome in men.

If the small Y chromosome gradually disappears, as we can read from time to time, would the gender problem also be solved?

It will not happen.

So for the moment we are left with two germ cells. If we transpose this model to the plant world, where we speak of monoecious or dioecious plants, could we not affirm that there are indeed two germ cells, but many sexes? After all, there are very varied flowers with more or less developed or mature reproductive organs. Everything is therefore possible, even self-fertilization.

Self-pollination is rare, however, and plants generally try to avoid it. The same goes for snails, which are hermaphrodites, but do not self-fertilize, but fertilize the eggs of another snail.

Does this mean that as variegated as plants are, they remain confined to two sexes and cannot be taken as an example for the current debate in society in order to open conceptual boundaries?

Yes, plants only have two sexes. In the social discourse on "sex-specific" behaviors, on the other hand, I would argue for talking about "gender," because then we would be at another level of explanation. Human beings are, as I always say, the most cultural of species.

So biology can't settle the debate about sex and gender?

As a scientist, I would say that the matter is clear: there are two sexes. Period. In our species as in the eight thousand or so other species of mammals. How we address someone, with this or that pronoun, is again a very cultural matter. I am of course in favor of everyone being able to live as they wish, always being treated with tolerance and respect, regardless of how the individual feels, without there being any value judgment. And these are cultural, political or social issues that do not concern my field of work.

Man is neither a fish nor a mouse, but what can animal studies teach us about gender?

Animals can serve as model systems, helping to develop drugs, for example, since mice are genetically closer to us than fish. Interestingly, however, no matter what method is used to determine the sex of an animal, there is always a male and a female in the end. I find it fascinating that something so fundamental in biology – and I maintain that there are only two sexes and no spectrum – can be created in such different ways, even within a family, genus or species.

Axel Meyer is professor of zoology and evolutionary biology at the University of Konstanz.

On the same subject, read also The fanatics achieve their goal