In class, though, some students argued instead that it is impossible to measure IQ in the first place, that IQ tests were invented to ostracize minority groups, or that IQ is not heritable at all. None of these arguments is true. In fact, IQ can certainly be measured, and it has some predictive value. While the score may not reflect satisfaction in life, it does correlate with academic success. And while IQ is very highly influenced by environmental differences, it also has a substantial heritable component; about 50 percent of the variation in measured intelligence among individuals in a population is based on variation in their genes. Even so, some students, without any evidence, started to deny the existence of heritability as a biological phenomenon.

Read: The war on stupid people

Similar biological denialism exists about nearly any observed difference between human groups, including those between males and females. Unfortunately, students push back against these phenomena not by using scientific arguments, but by employing an a priori moral commitment to equality, anti-racism, and anti-sexism. They resort to denialism to protect themselves from having to confront a worldview they reject—that certain differences between groups may be based partly on biology. This denialism manifests itself at times in classroom discussions and in emails in which students explain at length why I should not be teaching the topic.

To my surprise, some students even objected to other well-established biological concepts, such as “kin selection,” the idea that, when individuals take actions for the benefit of their offspring and siblings, they are indirectly perpetuating their own genes. Startled students, falling into what we call the “naturalistic fallacy”—the notion that what occurs in nature is good—thought I was actually endorsing Trump’s hiring of his family! Things have gone so far that, in my classes, I now feel compelled to issue a caveat: Just because a trait has evolved by natural selection does not mean that it is also morally desirable.

The duty of scientists is to study the world—including the human body and mind—as it is. Some of our students, however, are seeing only what they want to see and denying real-world phenomena that conflict with their ideology. Take, for example, the obvious biological differences between the sexes, not only in physical traits (men, on average, are clearly stronger and faster than women are), but also in aptitudes and preferences (boys generally prefer wheeled toys, and girls prefer plush toys, a preference that is also observed in baby monkeys!).

Read: Are male and female brains biologically different?

People expect an equal sex ratio across academic professions and sometimes ascribe the lack of such equality to bias. In the so-called STEM fields—science, technology, engineering, and mathematics—the relative paucity of women is frequently taken to reflect endemic sexism. While this is undoubtedly a factor, the effect of bias as opposed to other factors, such as differences in what male and female students prefer, requires detailed empirical study.