Final answer:
Heritability estimates can change over time due to epigenetic modifications and changes in population genetics, such as genetic drift and gene flow.
Step-by-step explanation:
Other than genetic mediation, two reasons why heritability estimates might change over time are epigenetic modifications and changes in population genetics. Epigenetic modifications are heritable changes in gene expression that occur without altering the DNA sequence itself. These modifications can be influenced by environmental factors and can affect how genes are turned on or off. Some changes can even be passed down to future generations. On the other hand, changes in population genetics can include mechanisms such as genetic drift, which is the change in the frequency of an existing gene variant (allele) in a population due to random sampling, and gene flow, which occurs when there is migration of individuals and genetic exchange between populations.