Population heritability estimates
Contributed by Michael Joyner
In the 1800s biometrics, the measurement and classification of human phenotype, emerged as a field of study. Early biometric studies showed for example that parental height could account for about 40% of the variance seen in children. As ideas about the biological basis of both between and within species phenotypic variability emerged post-Darwin, there has been a long lasting effort to determine the biological basis of heritability. This accelerated in the early 1900s with the rediscovery of Mendel’s work on clearly heritable phenotypic variation in plants. It also led to the coining of the terms gene, genotype and phenotype, and also the discovery of chromosomes as the cellular home of “genes”. The idea that phenotypic variability had a clear cut and mostly genetic explanation continued as the DNA centric view of “what is a gene” emerged in the 1950s. The shift in the definition of a gene also appears to have contributed to the idea that variability in DNA sequences would be the major driver of phenotypic variability. In this context, a frequently overlook concept is that estimates of heritability are also dependent on relatively stable environmental and cultural conditions. For example heritability estimates for body mass index (BMI, a measurement linked to body composition and used in the study of obesity) are dependent on both the socio economic status of the population being studied and also any recent changes in the socio economic status of the population being studied. Likewise in Japan heritability estimates for height since World War II are confounded by large generational increases in height due to improved nutrition in the absence of changes in DNA sequence. For many human phenotypes including the prevalence of many non-communicable diseases, migration studies show that environment, behavior and cultural factors play a major role in human phenotypic variation in the absence of DNA sequence differences. Observations such as these highlight the limitations of the DNA centric view of human phenotypic variation. They emphasize the idea that complex multidirectional interactions between the environment, behavior, physiological regulation and adaptation, and the genome explain human phenotypic variation.
|The MUSIC of Life: Biology Beyond the Genome ©Denis Noble|