Determining Evolutionary Relationships Summary

Summary

To build phylogenetic trees, scientists must collect accurate information that allows them to make evolutionary connections between organisms. Using morphologic and molecular data, scientists work to identify homologous characteristics and genes. Similarities between organisms can stem either from shared evolutionary history (homologies) or from separate evolutionary paths (analogies). Newer technologies can be used to help distinguish homologies from analogies.

After homologous information is identified, scientists use cladistics to organize these events as a means to determine an evolutionary timeline. Scientists apply the concept of maximum parsimony, which states that the order of events probably occurred in the most obvious and simple way with the least amount of steps. For evolutionary events, this would be the path with the least number of major divergences that correlate with the evidence.

Glossary

analogy

(also, homoplasy) characteristic that is similar between organisms by convergent evolution, not due to the same evolutionary path

cladistics

system used to organize homologous traits to describe phylogenies

maximum parsimony

applying the simplest, most obvious way with the least number of steps

molecular systematics

technique using molecular evidence to identify phylogenetic relationships

monophyletic group

(also, clade) organisms that share a single ancestor

shared ancestral character

describes a characteristic on a phylogenetic tree that is shared by all organisms on the tree

shared derived character

describes a characteristic on a phylogenetic tree that is shared only by a certain clade of organisms