David Linden - Unique: The New Science of Human Individuality

I SHOULD JUST LEARN TO RELAX AND ENJOY MUSIC, BUT I cant leave well enough alone. Case in point: Im 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!

Im singing along nowdoing 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. Its the curse of the geek to overanalyze. I start thinking about DNA. OK, she got her eyes entirely from her mammas and papas genes, but those thighs? Thats 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 thats 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? Theres evidence for this view as wellvariants 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, Im 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, shes funny and shes close to her friends. How did she get that way?

A S 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. Its a reasonable approach if one is trying to understand those aspects of biology that people (or mice) have in common. But its 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 thats been made bitter with quinine. However, it doesnt 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?