Why do scientists think that new genes arise by duplication of an original gene and divergence by mutation?

Explanation:

This is because of the fact that genomes of the organisms exhibit gene families and superfamilies. These contain genes that typically encode for proteins with similar aminoacid sequences, the proteins form by these aminoacids perform related functions. In this way the genes and their functions are duplicated among the gene families. This duplication of genes prevents the divergence from mutation.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

d. planting trees

the trees take in carbon to make oxygen.