question: What was the combination of effects that Darwin considered the most important in determining the differences in species that evolved separately in similar environments ?
answer: His explanation was a combination of migration and descent with modification .
turker_answer: His explanation was a combination of migration and descent with modification .
rule-based: The combination of effects that Darwin considered the most important in determining the differences in species that evolved separately in similar environments was his explanation was a combination of migration and descent with modification .