Final answer:
If everyone in a population had the exact same environment, the heritability of traits would be 100 percent, as all phenotypic variation would be attributed to genetic differences.
Step-by-step explanation:
Many traits are affected by both genetic and environmental factors. If everyone in a population had the exact same environment, the heritability would be 100 percent. Heritability is the fraction of phenotype variation that we can attribute to genetic differences among individuals in a population. The role of the environment becomes negligible when it is constant for all individuals in that population since all variation in traits would then be due to genetic differences. Hence, the more uniform the environment, the higher the heritability because differences in the phenotype among individuals are solely due to their genetic variance.