Genetic factors

NY Times says:

Q. What is the latest thinking on why there are more right-handed people than left-handed people? Is it genetic?

A. "The best thinking is that there is no genetic basis for it," said Dr. Lee Ehrman, distinguished professor of biology at Purchase College of the State University of New York, co-author of a new study in the journal Behavior Genetics, with Dr. Ira Perelle of Mercy College.

Dr. Ehrman's research, covering 12,000 people, led her to conclude that the reason for the predominance of right-handedness is that most people are born with the language-generating part of the brain primarily in the left hemisphere. Some nerve fibers from the language area cross over and direct the right side of the body, handling writing and some other learned tasks, leading to one hand's becoming dominant in these tasks.

Scientific American says:

What is really going on, asserts Oliver, a political scientist at the University of Chicago, is that "a relatively small group of scientists and doctors, many directly funded by the weight-loss industry, have created an arbitrary and unscientific definition of overweight and obesity. They have inflated claims and distorted statistics on the consequences of our growing weights, and they have largely ignored the complicated health realities associated with being fat."

One of those complicated realities, concurs Campos, a professor of law at the University of Colorado at Boulder, is the widely accepted evidence that genetic differences account for 50 to 80 percent of the variation in fatness within a population. Because no safe and widely practical methods have been shown to induce long-term loss of more than about 5 percent of body weight, Campos says, "health authorities are giving people advice--maintain a body mass index in the 'healthy weight' range--that is literally impossible for many of them to follow." Body mass index, or BMI, is a weight-to-height ratio.

I am skeptical when they talk about what is genetic and what is not.