{'fraction_non_alphanumeric': 0.020361990950226245, 'fraction_numerical': 0.01282051282051282, 'mean_word_length': 5.1270207852194, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The Role of Heritability in Adjusting Phenotypic Variability

The distribution of phenotypes within a population can be an important factor in population fitness (for measurements of individual fitness as a function of phenotype, see Barnes [1968] and Kearsey and Barnes [1970]). One mechanism for changing a distribution is to change the heritability of a trait by changing the genetic basis for variation in the trait. I will try to show that heritability can be an important aspect of adaptation. The distribution of continuously varying characters in a population is largely determined by three factors. Two of these factors, the reduction in variance due to mating and the increase in variance due to meiotic segregation of alleles in the production of gametes, have recently been analyzed by Roughgarden (1972) in his study on the evolution of niche width. A similar treatment of the distribution of continuously varying characters is given in Slatkin's (1970) paper on selection and polygenic characters. The point is made by both authors that the distribution of a character is a result of dynamic equilibrium between the collapsing effects of nonassortative mating and the spreading effects due to the variety of offspring phenotypes produced by individual pairs of parents. Indeed, they calculate that the variance of values for the population is about twice the variance within families. The third factor controlling the form of the distribution of offspring phenotypes is the heritability. For a given trait, the mean phenotype of the offspring produced by a given mating can be predicted to fall between the mean of the parents and the mean of the population. The extent to which the mean offspring phenotype resembles the midparent phenotype is the heritability (see Lerner 1958). Traits in which the variability arises from alleles which act independently of the rest of the genotype and the environment have a high heritability. Roughgarden's and Slatkin's models are based on 100% heritability, the mean of the offspring being the midparent phenotypes. If, however, the variability for the trait arises from alleles whose effects depend heavily on which other alleles are present, or on the environment, or allow what Milkman (1970) calls "stochastic variation," the heritability will be low. The extent to which the heritability is less than 100%o is, like mating, a factor collapsing the distribution toward the mean. The relationship between niche width and phenotypic distribution for a continuously varying character is the subject of Roughgarden's (1972) paper. In brief, he considers resources which can be ordered along an axis