“The concept is called ‘reverse inference.’ It’s both neuroscience’s greatest ambition, and the origin of its most frustratingly breathless overstatements.”
Every so often, a person is unexpectedly thrust into a defining wedge-issue of an era. This time, I was asked rhetorically, “Is being gay a choice”? Well, my friend answered their own question; according to a series of studies, including one published in Scientific Reports in 2018, scientists have discovered neurological differences between gay and straight people. When subjects were shown a series of pornographic pictures, depending on the content of the images, people with different sexual orientations had different brain activity. In other words, there is a concrete biological origin of sexuality; there is such a thing as a “gay” or “straight” brain—rather, a biologically-inevitably gay or straight brain.
As my friend concluded from this development, this proves that being gay is not simply psychological; there’s an actual biology to it. Those in right-wing chatrooms trying to mock gay people by saying things to the effect of, “I want to be a frog, therefore, I’m a frog” are now, scientifically verifiably, jerks. Just as one can’t just decide to be a frog, one cannot simply claim to be gay and then, poof, become gay.
Without science, if someone states his or her sexual preference, either he or she is telling the truth or making it up. Either a person is gay or they’re pretending to be. With science, however, maybe this debate can be resolved for good.
Personally, I do not have a strong position on when—in the course of one’s development—a person starts ‘being gay.’ I’ve seen scientific arguments for genetic destiny, but I’m also drawn to the idea that sexual preference is slowly shaped by an interplay of genetic and social factors throughout adolescence and even into adulthood.
I do, however, have a position on whether brain-imaging research supports the conclusion that being gay is a biological-inevitability. More importantly, I have a position on whether scientific research can inform our moral obligations towards supporting gay rights. In this essay, I hope to show that in specific, neuroscientific terms, we do not know with much confidence what being gay really is. Furthermore, even if we did, science cannot resolve the LGBTQ-rights aspect of the culture wars.
Brain Imaging Does Not Prove Biological Causation, and, Being LGBT is, in General, More than Sexual Orientation
Despite the involvement of extremely complex brain-recording technology, the design of the 2018 experiment was very simple. Scientists collected a group of people who were gay and another group of people who were straight, positioned them in a brain scanner, and showed them pornography. While the subjects awkwardly looked at naked bodies, researchers collected images of their brain activity, and, lo and behold, discovered that some areas of the brain showed differences.
However, one big issue is that straight people and gay people do not differ just in sexuality. There are also (in general) differences in personalities and lifestyles. What if the brain differences seen in this study are really just differences in social presentation? If being gay is (often) more than sexual preference, we can’t be confident that the neurological differences are strictly about sexuality.
This confound is not unique just to studies dealing with sexuality. The way we conduct brain-imaging today struggles to prove causation in a traditional scientific sense. Before scientists are willing to adopt the term “causation,” they want to see that the manipulation of some variable has an impact on another. In other words, changing X reliably changes Y. Sure, we can compare brain activity between groups; however, we cannot intervene in a way that truly mimics what we’re recording.
The problem is two-fold. Commonly-used brain-recording technologies like EEG and fMRI do not offer very precise resolution. Instead, they record from large swaths of brain tissue. With these technologies, we can evaluate whether a large population of cells are more of less active—but not what any individual cell is doing. It’s not clear whether neuroscience actually needs to know the functionality of each cell, but it’s clear that our recording technology provides highly ambiguous information.
The second half of the problem lies with the difficulty with brain stimulation. Non-invasive stimulation technologies (like transcranial magnetic stimulation) can be done pretty easily, but these technologies also lack precise resolution. In this case, even if our recording technologies provide un-ambiguous data, we could not intentionally produce that same activity pattern.
If we could reproducibly induce gay or straight preferences, we would know with real confidence that we had discovered the biological basis of homosexuality. Tangentially, if we had the technical capacity to change a person’s sexual orientation, it would open up a pandora’s box of ethical dilemmas (should a parent have the right to convert their child?). Fortunately, this horror scenario—like Mike Pence’s conversion-camp fantasy—is well beyond our technical capabilities.
A Bigger Problem; Neurosciences Persistent Fallacy
Perhaps, though, we ought to try a thought experiment. Let’s say it’s a little bit in the future, and a son just announced to his father that he is, in fact, gay. The father decides that he needs some verification, and, as such, the father takes his son to see the local scientist. The scientist explains that long ago, researchers identified the neural correlates to being gay, as described above, using the round-up and scan method. The scientist then tells the father that he can place the son in the scanner, and, after a short while, determine whether his brain has the characteristics that make his brain gay.
Neuroscientists have long hoped that a person’s mental state could be inferred based on the findings of a brain scan. What Russell Poldrack and many other neuroscientists have argued, however, is that this approach relies on questionable reasoning. If we understand a person’s psychology, the argument goes, we can also identify the underlying neurology. Just throw the person in a brain-scanner, and there’s your answer. However, going one step further—taking that newly discovered neurology—and inferring that same psychology in a different person is something of a logical leap.
X → Y does not imply Y → X, because sometimes, maybe, Z → Y. Also, some X’s are Y’s does not imply that all X’s are Y’s.
It’s pretty simple. Scientists might be able to observe that gay people, on average, have one sort of brain. But not every gay person’s brain is going to appear gay. Furthermore, some non-gay people may have brains that appear gay, even if they are not gay. The differences that scientists observe in the brain are based on group averages; they almost never perfectly distinguish between two groups of people, and, in the case of the study linked here, they did not appear to. The concept is called “reverse inference.” It’s both neuroscience’s greatest ambition, and the origin of its most frustratingly breathless overstatements.
However, enlightened neuroscientists do note that reverse inference is not necessarily wrong, and, at times, it may be useful. Even if we cannot be 100% sure that a particular brain region underlies a particular trait, maybe we can be 95% sure. Oftentimes, the correlations we find with brain imaging research are suggestive. Nevertheless, especially in situations where there is some variability in the neurobiology (which, is basically, every brain scan study), people need to be very cautious in making that final reverse inference.
Self-report is a premise of the argument, which means that science is not well-prepared to transcend self-report. If a person states that he or she is gay, neuroscience is generally not in a position to elaborate.
Neuroscience cannot tell us much about psychology without relying on current psychological measures. In order to conduct research, we have to have some operational definitions. In this case—if we want to identify the neural correlates of being gay—we have to rely on whether people say they’re gay. Self-report is a premise of the argument, which means that science is not well-prepared to transcend self-report. If a person states that he or she is gay, neuroscience is generally not in a position to elaborate.
As a scientist, I believe in the importance of science-advocacy, and I agree with the sentiment that much evil originates from humankind’s attempts to define and divide our species into various categories. I also believe that sexuality does not have to be a rigid unchanging quality defined at birth.
However, in this case, we are likely placing solidarity-signaling over neutral scientific reasoning. Confidently asserting the existence of inevitably-gay-brains might make for the ultimate alliance with the LGBTQ community, but it may overstate the confidence of our science. Scientists are allying with the LGBTQ community certainly not because of political identity, no, but because it’s rational to do, in their view—because it’s scientific to do so.
But some political questions transcend objective reality. Whether climate change is happening is science, whether we should do something about it isn’t. Whether or not we believe that a society ought to embrace homosexuality, or a government ought to protect LGBTQ rights, is a moral question, not a scientific one. The underlying scientific reality can inform our position on whether we support gay rights, but it’s only part of the equation.
Andrew Neff lectures in psychology at Rochester University and runs the blog Neuroscience From Underground.