Final answer:
A phylogenetic tree is a diagram used by scientists to show evolutionary relationships and divergence times among organisms, based on genetic and physical similarities and differences. The length of branches is proportional to the time elapsed since species diverged from a common ancestor, making it a visual representation of the hypothesized evolutionary pathway.
Step-by-step explanation:
A scientist constructing an evolutionary tree indicating relatedness and divergence times among taxonomic groups is making a phylogenetic tree. This diagram represents the evolutionary relationships among various biological species based on both genetic and physical traits. They are considered hypotheses of evolutionary connections, often reflecting the hierarchical classification of organisms by illustrating how taxa are related to one another through common ancestry. Phylogenetic trees also show divergence times from a common ancestor, with branch lengths being proportional to time elapsed.
Scientists collect accurate morphologic and molecular data to build these trees and use concepts like cladistics and maximum parsimony to organize evolutionary events. The internal nodes represent ancestral points of divergence leading to the formation of new species. Although traditionally resembling a tree, new scientific information about horizontal gene transfer and genome fusion has prompted some scientists to propose web or ring structures instead.