Scientists have been looking at bottlenose dolphins recently to try to figure out how menopause evolved. Even though dolphins don't go through menopause.
Killer Whales, Short-Fin Pilot Whales, False Killer Whales
But bottlenose dolphins' similarities to killer whales, short-fin pilot whales, and false killer whales--the only mammals apart from humans to undergo menopause--makes them a good study subject. After looking at data set of information about 229 female dolphins and their 562 calves over a period of 34 years, researchers found that calves born to older mothers are more likely to die by the age of 3 than calves born to younger mothers.
Researchers also found that older mothers nurse their later-in-life calves longer--5 years on average, and occasionally up to 8 years, as opposed to the 4 years typical for earlier calves--maybe to give them a better shot at surviving.
External Maternal Care
Especially since offspring born later in life have a lower chance of surviving, it makes sense for a mother to focus her energy on the offspring she already has rather than continuing to reproduce. It seems like a lot less work, too. Sounds like a good adaptation to me.
Sources And Further Readings:
- Karniski, Caitlin. Krzyszczyk, Ewa. Mann, Janet. "Senescence impacts reproduction and maternal investment in bottlenose dolphins." Proceedings of the Royal Society B Biological Sciences. July 18, 2018. DOI: 10.1098/rspb.2018.1123
- Morrell, Virginia. "Dolphins could unveil the origins of menopause." Science. July 17, 2018. Accessed October 23, 2018.