This hypothesis proposes that this crossing-over event occurred in a heterozygous catarrhine female sometime after the platyrrhine/catarrhine divergence.
He began to make significant contributions to the understanding of the relationship of genetic crossing-over and the microscopically observed events that the chromosome passed through during meiosis.
Hair texture alleles might be adjacent to highly selected loci on the chromosomes, which would lead to them coming along in crossing-over events in meiosis.