Prologue
I SHOULD JUST LEARN TO RELAX AND ENJOY MUSIC, BUT I can’t leave well enough alone. Case in point: I’m blasting down the highway on a fine sunny day when Juvenile comes on the car radio with that infectious New Orleans bounce and I start to bop in my seat.
Oh where she get her eyes from? She get it from her mamma!
Oh where she get her thighs from? She get it from her mamma!
Where she learn to cook from? She get it from her mamma!
I’m singing along now—doing the call-and-response and smacking the steering wheel to the beat. But on a parallel track my mind is already chewing on the lyrics. It’s the curse of the geek to overanalyze. I start thinking about DNA. OK, she got her eyes entirely from her mamma’s and papa’s genes, but those thighs? That’s probably a mixture of genes and learned eating habits. The population of bacteria resident in her gut affects her metabolism and hence the thickness of her thighs. Her mamma probably taught her how to cook, so that’s down to social experience. And we know from identical-twin studies that individual food preferences have only a small genetic component, so not much mamma (or papa) there. But perhaps she inherited the gene variant that confers supersensitivity to bitter foods. So her cooking style, which reflects her food preferences, is likely to be more complicated than the thigh situation. My train of thought only gets more convoluted as the song continues.
Why she swear that she the boss? She get it from her mamma!
Why she always gotta call the law? She get it from her mamma!
Where does her assertive nature come from? Was it how she was raised? Or perhaps the crucial influence of her peers? Have genes contributed to her confidence? There’s evidence for this view as well—variants in neurotransmitters and all that. Will she always feel like the boss and have the gumption to say so, or is this confidence just reflective of her present stage of life? We know that personality traits are somewhat changeable in children but are fairly stable in adults in the absence of major trauma.
Yes, I know that, to a large degree, I’m missing the point. Juvenile is not rapping to detail the experiences, developmental randomness, and genetic factors that shape us as individuals. Nonetheless, he raises many of the central issues of human individuality. The protagonist has a list of traits that we learn about as the song unfolds: in addition to being attractive, confident, and skilled in the kitchen, she’s funny and she’s close to her friends. How did she get that way?
AS A BIOLOGIST, I go to great lengths to minimize individual differences in my experiments. In my lab, we study strains of mice that have been inbred to be as genetically similar to one another as possible. Then, to further reduce variability, we take scrupulous measures to ensure that they are raised in the same boring lab conditions. We typically measure large populations of animals and then take the average of those measures to test our hypotheses. In order to see the central trend, we ignore the outliers. It’s a reasonable approach if one is trying to understand those aspects of biology that people (or mice) have in common. But it’s far from the whole story.
If I open up a box of lab mice, fresh from the breeder, I can see that they share certain traits. For example, they will all attempt to hide from bright light, they will all stand stock-still in fear when they smell fox urine, and they will all reject drinking water that’s been made bitter with quinine. However, it doesn’t take much observation to reveal important individual differences. Some mice are more aggressive toward one another and toward my grasping hand. In the absence of threat, some will race around the cage while others sit there calmly. Individual differences can also be found in physiological measures, such as resting stress hormone levels or sleep patterns or the amount of time it takes for food to pass through the digestive system.
How do they get that way?
FOR SEVERAL YEARS, NOT so long ago, I spent quite a bit of time on the dating site OkCupid, looking for my perfect match. For me, online dating was a fascinating, frustrating, and ultimately serendipitous process: I met my wonderful wife on that website. It turns out that meeting one’s future spouse online is not an unusual event these days. According to OkCupid cofounder Christian Rudder, in 2013 there were approximately thirty thousand first dates every night because of his website. Of those pairs, about three thousand became long-term couples and about two hundred eventually married (and presumably many others are in long-term, committed but unmarried relationships).1 One can only imagine that these numbers have increased significantly since 2013, and of course OkCupid is just one of many such sites.
For me, browsing dating profiles on OkCupid was a master class in human individuality. You probably know how it works. Each person provides basic information, photos, and answers to a set of questions in order to express who they are—or what version of themselves they imagine to be most appealing—and what sort of relationship they’re seeking. Importantly, a dating website is not an entirely public forum. Unlike a bar or some other real-world social space, the OkCupid user is not being observed by her friends and coworkers as she writes her profile. She can express herself in a way that’s less constrained by social pressures (or at least constrained by a different set of social pressures). Here’s a fictitious yet plausible example from my own urban, midlife demographic. Each line is from a real profile, but I’ve mixed many profiles together to create this composite.
CharmCitySweetie, 54
Woman, straight, single, 5’10”, curvy
White, speaks English and Spanish, graduated from university
Somewhat lapsed Roman Catholic, Scorpio
Never smokes, drinks socially, has dogs
Has kids, but does not want more
Seeking single men for long-term dating
I’m a typical eldest child from a big family.
I love witty banter, wry humor, and self-deprecation.
I work as a defense attorney.
I’m left-handed and proud of it.
I like to walk around the house with my toothbrush in my mouth.
I have a glue gun, and I’m not afraid to use it.
I’ve been known to get a little blue in the winter.
I like to get up really early and run with my dogs.
I’m always turning the thermostat up.
Both my mind and my browser have too many tabs open at the same time.
I like to sing and I have perfect pitch.
I pick my teeth with the mail when I think nobody is looking.
The first things people usually notice about me:
My long red hair.
The tattoo of a dancing platypus on my shoulder.
My Boston accent.
My perfect memory for song lyrics.
Favorite books, movies, shows, and food:
I don’t watch much TV, but I love scary movies. Right now, I’m reading and enjoying the new Jennifer Egan novel. I rock out to everything from sweaty punk to 70s soul music to Schubert. I like spicy food and hoppy beer but despise mayonnaise, mustard, and runny eggs. Red wine is not optional for my happiness.
You’re not standing in front of your boat, toilet, motorcycle, or car in your profile picture.
You know what a “mensch” is and you are one.
You won’t mind my cold feet on your back.
You can bring it.
Like the protagonist of Juvenile’s song or a mouse in my lab, CharmCitySweetie became her particular adult self. How did she come by her Boston accent, her heterosexuality, her curvy figure, her sense of humor, her chilly feet, her taste for IPAs, and her perfect pitch? It turns out that there’s a different explanation for each of these traits.
How we become unique is one of the deepest questions that we can ask. The answers, where they exist, have profound implications, and not just for internet dating. They inform how we think about morality, public policy, faith, health care, education, and the law. For example: If a behavioral trait like aggression has a heritable component, then are people born with a biological predisposition toward it less legally culpable for their violent acts? Another question: If we know that poverty reduces the heritability of a valued human trait like height, should we, as a society, seek to reduce the inequities that impede people from fulfilling their genetic capacity? These are the types of questions where the science of human individuality can inform discussion.
Although investigating the origins of individuality is not just an endeavor for biologists—cultural anthropologists, artists, historians, linguists, literary theorists, philosophers, psychologists, and many others have a seat at this table—many of this topic’s most important aspects involve fundamental questions about the development, genetics, and plasticity of the nervous system. The good news is that recent scientific findings are illuminating this question in ways that are exciting and sometimes counterintuitive. The better news is that it doesn’t just boil down to the same tiresome nature-versus-nurture debate that has been impeding progress and boring people for years. Genes are built to be modified by experience. That experience is not just the obvious stuff, like how your parents raised you, but more complicated and fascinating things like the diseases you’ve had (or those that your mother had while she was carrying you in utero), the foods you’ve eaten, the bacteria that reside in your body, the weather during your early development, and the long reach of culture and technology.
So, let’s dig into the science. It can be controversial stuff. Questions about the origins of human individuality speak directly to who we are. They challenge our concepts of nation, gender, and race. They are inherently political and incite strong passions. For over 150 years, from the high colonial era to the present, these arguments have separated the political Right from the Left more clearly than any issue of policy.
Given this fraught backdrop, I’ll do my best to play it straight and synthesize the current scientific consensus (where it exists), explain the debates, and point out where the sidewalk of our understanding simply ends. And if you want to keep your internet dating browser window open as you read, rest assured that I won’t judge you.