One thing we have in common with elephants is our long lifespan, specifically past their reproductive prime. African elephants can live for as long as 16 years after producing most of their offspring. But why did this trait evolve and what purpose does it serve?
In order to answer this question, researchers¹ analyzed data collected over a 40 year period from 834 wild female African elephants living in Amboseli National park in southern Kenya. The elephants were tracked over the course of their lives, many from birth until death, and from this rigorous research a picture began to emerge.
Amboseli elephants start giving birth, on average, at around 14 years of age and produce 95% of their offspring by the time they reach 50, yet they can live for as long as 16 additional years! As they age, they reproduce at a slower rate but overall, their long survival allows them to produce more young than shorter lived species¹. And there seems to be no trade-off to reproduction; that is, the age at first reproduction and the rate of reproduction do not decrease the overall survival of female elephants¹.
The rate of reproduction of female elephants decreased as they aged but elephants who lived the longest had a reproductive advantage, producing more young throughout their lives. In addition, daughters of mothers who were longer lived themselves had a longer lifespan.
Elephants who reproduced while their mothers were alive had higher rates of reproduction. Grandmothers provided care and attention to their grandchildren even when they had their own offspring. It was found that older females only rarely stopped reproducing entirely nor did they decrease the quality of care given to their own offspring in their old age, even while they were giving care to their grandchildren. In addition, other studies² have suggested that older females serve as “repositories of knowledge”, help protect calves and keep family units together².
So, why live long? The authors of the study suggested “that longevity has reproductive advantages, which are shared with family members through grandmothering, and thus an extended lifespan with prolonged fertility has been under positive selection”¹, and has thus evolved.
¹ Lee, Phyllis C., Victoria Fishlock, C. Elizabeth Webber, and Cynthia J. Moss. “The reproductive advantages of a long life: longevity and senescence in wild female African elephants.” Behavioral ecology and sociobiology 70, no. 3 (2016): 337–345.
² Moss, C. J., and P. C. Lee. “Female reproductive strategies: individual life histories. In ‘The Amboseli Elephants: A Long-Term Perspective on a Long-Lived Mammal’.(Eds CJ Moss, H. Croze and LPC Lee) pp. 187–204.” (2011).
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