User:Hgthacker/sandbox

Older females play a key role in the rearing of calves in some odontocete species, namely in Killer whales, Short-finned Pilot whales, Narwhals, and Beluga whales. These species exhibit an unusual life history characteristic known as post-reproductive lifespans, which entails a significant portion of female life-years in a population lived post-reproduction. It is thought that the unique social structures of these odontocete species favors post-reproductive life-spans due to an increased relative fitness of older females who care for and help rear young calves.