Note that in older men presence of a bushy beard is combined with baldness on the crown.Basics of beard growth James Hamilton and colleagues conducted pioneering studies of human beard growth in the 1950s/1960s, and notable research by Valerie Randall followed.Natural selection, whereby environmental features favour particular adaptations, is the keystone of the Darwin/Wallace theory of evolution.But Darwin soon recognized a second kind of selection.
He noticed that his beard grew less during spells on the island but began to increase the day before he left, reaching unusually high levels during his first few days on the mainland.
Darwin specifically cited the human beard as a response to sexual selection serving mate attraction. Wallace photograph by Sims, 1889; Wellcome Images; Creative Commons Attribution 4.0 International license.
Darwin photograph by Julia Margaret Cameron (1815-1879); work in the public domain.
Allowance was also made for differences between short-term and long-term relationships.
Computer graphic manipulation was used to generate male faces with five different degrees of masculinity and varying from clean-shaven through light or heavy stubble through to fully bearded.