Final answer:
High heritability does not mean a trait is solely determined by genes because most traits are polygenic and influenced by environmental factors. Heritability measures genetic variance, but phenotypic variation can occur due to environmental influences even in individuals with the same genotype.
Step-by-step explanation:
High heritability of a trait does not always indicate that the trait is predominantly determined by genes. Many human characteristics are polygenic, meaning they are controlled by multiple genes, and this includes traits like height, skin color, and weight. For example, eye color in humans is determined by more than eight genes, with multiple alleles in the population, such as the three different alleles that encode ABO blood type. Environmental factors also play a significant role, affecting phenotypic variation even among individuals with the same genotype.
Heritability is a measure of genetic variance among individuals in a population, yet environmental influences can cause two individuals with identical genotypes to express different phenotypes. This complexity suggests that while genetics are important, they are part of a larger interplay that includes environmental influences. Thus, a high heritability score does not necessarily equate to a trait being strictly genetically determined.