With the advent of genetics, the modern synthesis line of thought became concerned with functional studies that involved major evolutionary changes. This line of thought identified "major groups" and stated that in the early phase of a radiation of a major group there were many possibilities of form and function, but that in later phases only successful forms and functions survived. This line of thought also states that there is a natural genetic relationship between form and function, with a strong sense that form is dominated by function.
Knowledge of genes and crhomosomes produced the modern synthesis line of thought.