We know larger animals tend to have longer lifespans. But why do big cats(like leopards, etc)have such a short life(about 15 years) compared to humans(about 80 years)?

Question

p.s.Big cats and humans have similar body weights, if not higher.

In: Biology

Answer 1

Animals need to die to let newer generations take over, and how long their lifespan is depends on the pressures the species face (predation, toxins, cumulative damage, etc.)

Animals like mice that face a lot of predators don’t evolve longer lifespans because it’s not beneficial, they’ll still get eaten early on and evolution won’t have a chance to weed out the short life genes and favor the longevity genes.

Animals like lions don’t evolve human-like lifespans because their harsh life means they get a lot of injuries and illnesses that wear them down over time. Longevity genes can’t protect you against being gored by a water buffalo, or having your bones broken by a giraffe trampling.

Along with this, animals with faster metabolisms have shorter lifespans because they create more metabolic waste and therefore they accumulate more damage to their bodies in the same amount of time. This also applies to carnivores: animals who eat meat have much higher rates of cancer than their herbivorous counterparts. (Source: https://www.nature.com/articles/s41586-021-04224-5)

The only reason why larger animals generally have longer lifespans is because small prey animals can get away with short life’s and still successfully reproduce, while larger species take more time to grow up and reach maturity. Humans cannot have the two-year lifespan of a mouse because we’d still be toddlers by the time.

Primates in general have a lot of the characteristics that both allow and require longer lifespans: they’re larger than the average mammal, have slower metabolisms, eat mainly plants, and have long growing-up periods (primates are smart and need to do lots of learning to do things other species do by instinct) before maturity. A 100-pound chimp can live to its late 40s and early 50s with modern medical care.

However, humans are outliers and break the trend in a few of these aspects. Yes, we are the second largest primate after gorillas so that helps, but we have a faster metabolism than other apes (a 120-pound adult human will burn around 20% more calories than a 120-pound chimp, and 40% more than a similarly-sized gorilla), and are highly omnivorous with a significant portion of our diet being animal products, yet our lifespan is often double that of the other great apes. Even people living in the wild like hunter-gatherers regularly live to their late 60s and 70s, which is unheard of in any other primate, or really any mammal our size.

There are a lot of theories as to why this happened, but many people who study this agree that humans evolved such long lifespans because unlike other animals, grandparents are helpful to keep in a tribe in a survival and welfare sense: elders have deep knowledge of their environment which helps in times of crisis like droughts or natural catastrophes, they can help take some of the workload of raising kids so that the younger parents are more efficient at doing the more physically-demanding tasks, etc.