Dr Ulrich Kutschera, professor of evolutionary biology and physiology at the University of Kassel, Germany, and a visiting scientist in Stanford, California, has had a distinguished scientific career. He is an expert in the reproductive behaviour and parental care patterns of leeches and other animals, and the author of some 300 scientific publications plus 12 books on a variety of topics related to the biomedical sciences.

A sturdy defender of Darwinian evolution, he was drawn into a discussion of gender studies a couple of years ago. In interviews he argued that gender ideology is incompatible with biological facts and theories. After severe criticism from feminists and gender theorists, he published a controversial book in 2016: Das Gender-Paradoxon. Mann und Frau als evolvierte Menschentypen (The Gender-Paradox. Man and Women as evolved types of Humans). A second edition appeared earlier this year (1).

We queried Professor Kutscher about his research into gender studies and the reception of his book in Germany.   

* * * * * * * *

MercatorNet: As a biologist, what was your interest in critiquing the gender studies movement in Germany, the US, and the UK?

U. Kutschera: My involvement in this area stems from my experience as a leech scientist. Over the past four decades, I have observed numerous times that, in some of these aquatic hermaphrodites, sex and violence are interconnected phenomena. Some of these annelids perform traumatic inseminations. After internal fertilization of eggs (the sex act), they change their gender role: first, they act as males, and then as females (distribution of sperm vs. provision of egg cells, followed by cocoon production).

As you can see, sex and gender are key terms in evolutionary biology. Since we descended, with modifications, from a pre-Cambrian ur-bilaterian which was organized like a leech (or earthworm), the mechanisms of sexual reproduction are highly conserved processes.

In short, humans behave, in a number of respects, like leeches, which can also be loving parents. I discovered earlier in my career the phenomenon of parental care, combined with feeding of young, in some leech species. However, we are gonochorous (unisexual), while leeches are hermaphroditic.

Nevertheless, fertile men (distributors of sperm) and women (providers of egg cells with the capacity to get pregnant and give birth) display “archaic” behaviours preserved over millions of years of evolution. Based on these insights, I have analyzed and critically evaluated the “gender movement” in the context of sociology.

MercatorNet: You criticize gender studies as unscientific. Why? And how was your book received in Germany?

U. Kutschera: Based on my studies of the reproductive behaviour of a number of animal and plant species, plus my debates with German creationists, I was well prepared to explore the strange world cultivated in some university humanities-departments.

From my historical research I learned that the basic tenets of the gender worldview can be traced back to the writings of the American psychologist John Money (1921–2006). Based on studies on intersex-babies (which he erroneously regarded as “hermaphrodites”), Money argued in 1955, with reference to his work on “hermaphroditism”, that “sexuality in humans is undifferentiated at birth and becomes differentiated as masculine or feminine in the course of the various experiences of growing up” (1).

However, Money’s idea of the alleged birth of unisex babies, followed by socialization as boys or girls, has been refuted. The tragic case of David Reimer (1965–2004), whose parents followed Money’s advice, helps to prove that. Today, we know that in 99 percent of all humans, gender-identity is fixed long before birth and only marginally modifiable by education.

In my book, I describe the basic tenets of gender ideology or “Moneyism” and reject its basic claims. As expected, it was sharply criticized, mostly by social scientists involved in gender studies. However, quite a number of readers were delighted with its arguments.  

MercatorNet: What light does evolutionary psychology shed upon the phenomenon of homosexuality?

U. Kutschera: Evolutionary psychology can be traced back to the writings of Charles Darwin (1809–1882). As you know, Darwin was a purely naturalistic thinker who valued facts and rejected unproven claims. The consensus of recent research is that homosexuality is, in most cases, determined before birth. Hormonal processes that take place during the developing embryo and foetus lead to a fixed gender identity. However, it can also, in rare cases where they are not running as in the majority of men and women (about 97 percent), led to an erotic attraction to the same sex. Based on our current knowledge, it is fair to conclude that homosexuality in men (and woman) is, in the majority of cases, an inborn phenomenon and not a “life style”, as proposed by adherents of Money’s gender worldview.

MercatorNet: What do you think about the legalisation of same-sex marriage? Does it have an evolutionary future?

U. Kutschera: In my view, there is absolutely no justification for discrimination against gays or lesbians. These men and women have not chosen their destiny, but in most cases, are attracted to the same (rather than the opposite) gender – due to irregular hormonal (or immunological) processes that took place before birth.

In my personal view, marriage should be restricted to heterosexual couples, because the deeper sense of such a long-term relationship is the creation of progeny. Although about 15 percent of all men and women are infertile, most heterosexual couples want, via marriage, to establish a family with own biological children (1, 2). Since sexual reproduction is, for obvious reasons, not possible between couples of sperm or egg producers (see my leech studies mentioned above), same-sex-duos are by definition infertile. Hence, they have no evolutionary future, as defined by the spread of their own genes. The government should have no interest in granting them financial tax benefits, because they cannot procreate. However, the German state should be interested in children – they are the future of every society and country.

MercatorNet: From an evolutionary standpoint, children raised by same-sex couples are not in the mainstream. How could they be affected? Is there a difference between children conceived by biological parents and children who are adopted?

U. Kutschera: As described in my book, a biological mother and a biological father are both very important for a healthy development of the baby and child (1). To deny a child its natural mother or father is always a very problematic social experiment. Numerous studies have shown that stepfathers (or stepmothers) kill children under five up to 100 times more often than biological parents do. This “Cinderella-effect” always poses a danger when genetically unrelated adults raise children that are not their own (1, 2). There may be some same-sex couples who can manage all of these problems, but in general, such artificial (genetically unrelated) “families” are far from ideal. In many cases they are dangerous for the adopted children, as the literature shows (1, 3).

MercatorNet: You have starkly warned of families headed by same-sex couples in the context of the danger of paedophilia and sexual abuse. Why?

U. Kutschera: In both lesbian couples and gay couples, one natural parent – either a father or a mother – is missing. This is also relevant when considering surrogate motherhood. Lopez and Klein (3) have shown that, in most cases, fatherless or motherless children, with a stepparent as replacement, develop severe psychological problems.

The desire to know “Where do I come from?” is a universal human question. But in same-sex families that innate longing to know his or her genetically-related kin cannot be answered. I refer to Lopez and Klein’s book (3) for more information on this topic. Concerning the danger of paedophile interactions between male foster parents and adopted boys, I refer readers to two books by the clinical psychologist Richard B. Gartner (4, 5). In them, you will find case studies and detailed analyses that are far beyond what I have summarized in my Gender-Paradoxon (1).

MercatorNet: How do you respond to recent studies which show that homosexuality is also found among animals?

U. Kutschera: For 40 years I have been studying the sexual behaviour and gender roles of a number of organisms, such as annelids, myxomycetes and bacteria (which horizontally transfer DNA). When I critically evaluate the pertinent literature on the alleged “homosexual acts” in animals, I come to the conclusion that only males in domesticated sheep may behave similar to humans, when it comes to their same-sex erotic interactions (1).

However, if you carefully study the pertinent research papers on the alleged “gay rams”, these experiments and interpretations become questionable. The point is that all animals labeled as “homosexual” exclusively reproduce (via copulation and fertilization, i.e., sex acts) during a narrow time period, whereas humans are, in principle, over many decades of their life, “sexually mature” creatures.

In my opinion, homosexuality in humans and experimentally induced “male on male mountings” in some domestic sheep (but not in free-living populations of the same species) are different phenomena. More research is required to further elucidate the claim that true homoerotic interactions occur in animals. In most of these cases, the “homo-partner” will copulate with the opposite sex when it is in the right, sexually mature developmental stage. At most, these animals may possess a tendency for bi-sexuality (1).

MercatorNet: Do you think that same-sex marriage has received appropriate scientific scrutiny by academics and public policy professionals?

U. Kutschera: The problem is that many of these studies were carried out without consideration for the well-being (or feelings) of the adopted children. Usually, gay vs. straight parents are asked a number of questions about their under-aged adoptees. Naturally, gay parents contend that everything is OK with their adopted boy or girl, but heterosexual couples tend to admit that there are problems concerning discipline, education etc.

These studies are then widely reported in the popular press and send the message that “gay couples are better parents” than heterosexual parents. I want to refer to the Lopez and Klein-monograph (3), as well as the books of Gartner (4, 5), and also to Robert Sapolski’s extensive discussion of the importance of mothers for the well-being of children (2).

If you have internalized the facts and data summarized by these experts, you may understand why a “sex-and-gender-leech-scientist” like me has strong reservations about experimentation with little children, who have a right to be raised by their biological mother and father. Only when one parent dies, for instance by an accident, there will be a need for an unrelated replacement. However, a solution should be sought that is in the best interest of the child, i.e., a heterosexual couple as foster-parents (1, 2, 3).

MercatorNet: A final question – in your book on gender, you refer to the life and work of composers such as Bach, Händel, Telemann etc. Moreover, you discuss in detail the different abilities of men vs. women to create music. Why?

U. Kutschera: As you can see from my Wikipedia-CV, I have studied, at the University of Freiburg (Germany), biology/chemistry and the theory of music. The reason for this special interest in classical music is that I learned to play the piano when I was nine years old, and have continued this hobby ever since. At 26, when I was a PhD-student, I started to record my own compositions in a professional studio. Some of my Piano & Synthesizer-work, composed-performed in a Neo-classical style, has recently been published on 3 Compact Discs (Vols. 1 – 3). It is not unusual that scientists are also musicians, but this would be the topic of another discussion.  

Dr Ulrich Kutschera is professor of evolutionary biology and physiology at the University of Kassel, in Germany, and a Visiting Scientist in Stanford, California, USA. He is the author of Das Gender-Paradoxon. Mann und Frau als evolvierte Menschentypen (The Gender-Paradox. Man and Women as evolved types of Humans).


(1.) Kutschera, U. (2018) Das Gender-Paradoxon. Mann und Frau als evolvierte Menschentypen. 2. Auflage. LIT-Verlag, Berlin.

(2.) Sapolsky, R. M. (2017) Behave. The Biology of Humans at Our Best and Worst. Penguin Books, New York.

(3.) Lopez, R. O., Klein, B. (Eds.) (2016) Jephthah’s Children. The Innocent Casualties of Same-Sex Parenting. 2. Ed. Wilberforce Publications Ltd., London.

(4.) Gartner, R. B. (Ed.) (2018) Understanding the Sexual Betrayal of Boys and Men: The Trauma of Sexual Abuse. Routledge, Abingdon.

(5.) Gartner, R. B. (Ed.) (2018) Healing Sexually Betrayed Men and Boys: Treatment for Sexual Abuse, Assault, and Trauma. Routledge, Abingdon.

Ulrich Kutschera, PhD, is a Professor of Biology, author and composer-musician at AK Evolutionsbiologie in Freiburg i.Br., Germany, and Scientific Collaborator at research Institutes in Stanford, California...