Three interesting paragraphs from Matt Ridley’s Nature via nurture: Genes, experience, and what makes us human (Harper Collins: 2003).
It cannot be right to say that Hermia’s intelligence is caused by her genes: it is obvious that you cannot become intelligent without food, parental care, teaching, or books. Yet in a sample of people who have all these advantages, the variation between who does well in exams and who does not could indeed be a matter of genes. In that sense, variation in intelligence can be genetic.
Through accident of geography, class, or money, most schools have pupils from similar backgrounds. By definition, they give these pupils similar teaching. Having therefore minimized the differences in environmental influences, the schools have unconsciously maximized the role of heredity: it is inevitable that the difference between the high-scoring and the low-scoring pupils must be set down to their genes, for that is just about all that is left to vary. Again, heritability is a measure of what is varying, not what is determining.Matt Ridley’s – Nature via nurture: Genes, experience, and what makes us human (Harper Collins: 2003).
Likewise, in a true meritocracy, where all have equal opportunity and equal training, the best athletes will be the ones with the best genes. Heritability of athletic ability will approach 100 percent. In the opposite kind of society, where only the priviledged few get sufficient food and the chance to train, background and opportunity will determine who wins the races. Heritability will be zero. Paradoxically, therefore, the more equal we make society, the higher the heritability will be, and the more genes will matter.
In this video, geneticist ans psychologist Robert Plomin shows how much genes affect personality.