David J. Linden is a Professor in the Department of Neuroscience at the Johns Hopkins University School of Medicine. He is the author of Unique: The New Science of Human Individuality, The Accidental Mind: How Brain Evolution Has Given Us Love, Memory, Dreams, and God, The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good, and Touch: The Science of the Hand, Heart, and Mind. His laboratory has worked for many years on the cellular substrates of memory storage, recovery of function following brain injury and a few other topics.

THE CREATIVE PROCESS

Genetics and experiences, it's so fascinating. You know, we’ve all taken in a lot of this received wisdom without realizing it through the generations. From the way farmers breed plants or domesticated animals to indigenous knowledge, but it’s a complex science. What initially drew you to it?

DAVID J. LINDEN

It's a fundamental human question, how do we become individuals? It's a basic thing about being alive and thinking. Nature versus nurture is a phrase that was popularized by Francis Galton in the late 19th century. and the idea behind it is that if you were to look at a particular trait, say, shyness or height, you could say, well, to what degree can we attribute height to nature? In this case, meaning the gene variants that you inherit from your parents versus nurture in this case, meaning how you were raised by your parents and by your community. And I have many problems with this expression. Part of it is that the nature part shouldn't just mean genetics. In other words, there's all kinds of biological things that are not genetic things. If your mother fought off a viral infection while you were developing in utero, then you have a much higher chance of developing schizophrenia or autism when you grow up. Now that's biological, but it's not hereditary. That's not something that you would then acquire and then pass on to your own children. It only happens in the one generation. The other problem is when we hear the word nurture, we really focus on the family, how your parents raised you or failed to raise you, how your community was involved. And those things are very important, but they're far from everything that impinges upon you in your life. I take experience as the thing to substitute for nurture because it is much more inclusive and it includes not just social experience from your family and your peers and your community, but also experience in the more general sense.

THE CREATIVE PROCESS

And of course there’s a complex calculation and you can't say that applies to everyone, whether it's experience, genetic, environmental, these are just some of the new ways of thinking about gender identity at the moment. You know, is it genetic? What matter does choice play? And there are environmental changes to our diet and the water and that changes the hormonal balance in our bodies because there are hormones in our water and in our foods.

LINDEN

We know a lot more about sexual orientation (who you like), than about gender identity (who you feel yourself to be) because gender identity it's really only being studied in an effective way in the last few years. And the studies we have rather few people in them, and they're not yet that reliable. What we do know about sexual orientation is that it is partly heritable, but it's pretty weak. In other words, if you just look at studies of families, and you look at, in particular studies of either fraternal or identical twins that were either adopted and raised together or apart, which is the geneticist's favorite way of trying to untangle these contributions, what you come out with is that in cisgender males, about a 25% of the variation in sexual orientation can be attributed to gene variants and in females the number is slightly different. I can't actually bring that number to mind. I think it's in the ballpark of about 20%.

So these are significant effects, but they're far, far, far from the whole story. It's not like height, which is 80% heritable or earwax type, dry or wet, which is 100% heritable and is a very unusual trait like that. Neither is it like speech accent, which is 0% heritable and is entirely dependent by the people you heard speak in the early years of your life, particularly your peers.

So there is a small genetic but significant genetic component to sexual orientation. And it's slightly different in males and females. And interestingly, it's not general. So for example, if I were to have a gay brother, then the chance of me being gay would become higher. But if I have a lesbian sister, that does not change the chance of me being gay or vice versa.

If a woman has a lesbian sister, then the chance of her being attracted to women is higher. And if she has a gay brother, it doesn't make any difference at all. So it's not like gayness or straightness is what heritability is acting on. It's attraction to males or attraction to females. And that's a subtle distinction, but I think it's very important.

The other thing that is really interesting and fascinating is that there is, from a big meta-analysis that was done by the American Psychological Association, there is really no evidence whatsoever that links events in the family to your probability of being gay or straight or bi. So, well, that's a mystery.

If it's not how you were raised by your family and it's only a little bit genetic, what is it? Well, you know, I think you had a hint of some of it when you're talking about hormones. There is some evidence that hormonal exposure in utero matters. So, for example, if biologically female fetuses are exposed to what we call androgens, the class of male hormones, that includes testosterone, that increases the probability that the child who is born and then grows up will be attracted to women when they grow up. Even if that child is biologically female. Likewise, there seems to be something similar for gay men and exposure to estrogen and female sex hormones. That said, there's of course mystery. We're far from understanding in totality how the trait of sexual orientation arrives. And we also know that there are enormous cultural influences. There are societies that have sort of a revered place for homosexual behavior in the Pantheon and others where it is really looked down upon, and that seems to have influence on how this trait develops.

THE CREATIVE PROCESS

I often find this element of accident or chance happens during the process of improvisation. As an artist, I often feel like the less I know, the more I know how to do it. The less I'm aware, the more I can tap into these things. And it might be just going back to these traits that we might have needed before and now we don't use them, but somehow we know how to do it without knowing how to do it.

LINDEN

I think you could certainly make the case that creativity has been useful for a long time in human evolution and probably in our pre-human ancestors as well. So it's not surprising that that creativity is manifest in all kinds of ways from building a trap to catch a critter, to musical improvisation, to making a sculpture.

THE CREATIVE PROCESS

Indeed and what you watch in the animal world is that often creativity might arise from a need to survive. Whether you see it in the murmuration of birds or fish moving in these wonderful patterns to evade predators. We had conversations about improvisation with musicians, and there were tests, brain scans conducted during improvisation that indicated that it’s about losing the sense of self. Like something happens during these performances that their sense of self somehow dissolves and the musicians become beyond oneself.

LINDEN

If I were to look at a brain scan and someone said, "Point to me the region that has the sense of self." I don't know that I could actually do that. So in other words, I accept this notion as a higher-level explanation that can be really useful. I would say our ability to reduce that to brain regions and brain activities now is still really not there. I'm not saying it will never be there. It may emerge, but it hasn't emerged yet. Sense of self is a really, really interesting idea and it's something that fascinates me because it is used both kind of at a very high level, in a cognitive way, but neuroscientists think of sense of self more in terms of our senses that literally point inward. So when we think about the senses, we usually think about things like touch or vision or taste or smell or hearing that are designed to tell us, not about our own bodies, but about the external world. But we also have all these senses that are interoceptive rather than exteroceptive. And they're telling me things like, how is my head oriented relative to gravity? That's my balanced vestibular system. Where are my limbs in space at this moment that I can do, even with my eyes closed? I know where my arm is even with my eyes closed because I'm getting information from my muscles that is being sent to my brain. I know how distended my bladder is and whether I'm going to need to go to the bathroom soon. I know my immune state, my breathing, my blood chemistry, my digestion. All of these things are senses of self and the degree to which they influence higher cognitive processes is to me one of the really fascinating questions of neuroscience right now and one that we're just really starting to understand.

This interview was conducted by Mia Funk and Callie Cho with the participation of collaborating universities and students. Associate Interviews Producer on this episode was Callie Cho.

Mia Funk is an artist, interviewer and founder of The Creative Process & One Planet Podcast (Conversations about Climate Change & Environmental Solutions).