You’ve heard of the TV series Arrested Development, but did you know that arrested development is also an evolved reproductive strategy for some male orangutans? Adult males of this red-haired Indonesian ape species typically develop a massive size accompanied by beards, throat sacs, and protruding cheek flanges. A mature male orangutan is the primary mating partner of several females in his home range and is aggressive toward intruder males. This polygynous mating pattern leaves many males without ranges. Natural selection has hit on a unique adaptation for less fortunate male orangutans: arrested development. Some adult males do not develop secondary sexual characteristics. With low levels of growth hormone and testosterone, they can remain in a developmentally “arrested” state for up to 20 years, allowing them to pass as adolescents in the eyes of dominant flanged males even though they are sexually mature and frequently sire offspring.
Dr. Sylvia Amsler is a lecturer in anthropology at the University of Arkansas at Little Rock.