On Westwood Boulevard in Los Angeles, just off the University of California campus, the street is jammed at lunchtime. The tones of all humanity flow past, faces from Santa Monica, Singapore, and Senegal, a stroboscopic stream of light and dark.
Notwithstanding such contrasts in appearance, comparisons of our DNA show that human populations are continuous, one blending into the next, like the spectrum of our skin coloring. We all carry the same genes for skin color, but our genes responded differently to changes in solar intensity as bands of Homo sapiens migrated away from the unrelenting sun of the equator.
Still, it seems to be human nature to assign types to our fellow humans and then make judgments based on those types. Take this tall woman coming along the sidewalk and entering an Italian restaurant. Blond, but not California blond. In her early fifties, wearing a stylish suit and elegant shoes — a European. Physically she belongs to what one observer has called “the fair-skinned, fair-haired, gray-to-blue-eyed, long-limbed, relatively narrow-faced individuals that constitute a substantial portion of the population of Sweden, Denmark, Iceland, Norway, western Finland.” That is, the Nordic type.
Leena Peltonen is one of the world’s leading medical geneticists. In 1998 she was recruited from Helsinki University to become the founding chairwoman of the Department of Human Genetics at UCLA’s medical school. Trained as both a physician and a molecular biologist, she has discovered the genetic sources for many rare diseases, such as Marfan syndrome, a connective-tissue disorder. She has also found hereditary links to more prevalent conditions, such as multiple sclerosis, schizophrenia, osteoarthritis, and migraine.
The raw material for her investigations is DNA collected from people in Finland. Research by Peltonen and by her compatriots Juha Kere, Jukka Salonen, Albert de la Chapelle, and Jaakko Tuomilehto have made Finland into a sort of DNA laboratory for mankind. Now its scientists are detecting the heritable imprints of heart disease, diabetes, and asthma. The country’s contributions to medicine and genetics are far out of proportion to its size and population of 5 million.
