Most females in the wild do live longer than their male counterparts, although there are many exceptions. There are several theories and explanations for this trend.
It is somewhat common knowledge that women tend to live longer than men. Some say this is because females have better lifestyles; there are fewer female smokers and drinkers, and they have healthier eating and exercise habits, as well as an overall more conscientious lifestyle. There are many other social and scientific reasons for this.
Does this trend also extend into the animal kingdom?
As it turns out, it usually does! Most wild species do demonstrate longer female lifespans, as compared to their male counterparts. Just as for humans, many theories have been put forth to explain this pattern among animal species, but like everything else, there are plenty of exceptions to the rule.
Which animal groups show differences in lifespans?
Most mammals show longer female lifespans, such as whales, African lions, apes, some monkeys, and many more.
A few species show almost no longevity difference between the sexes, such as Japanese macaques, kangaroo rats and savannah baboons. Surprisingly though, despite our closeness to dogs and cats, not much is known about this aspect of their lives.
The humble fruit fly, the legendary Drosophila (arguably the most studied insect in history), shows conflicting results and is generally accepted as having equal longevity in both the sexes.
Some other well-known examples of longer female lifespans can be found in angler fish—a deep-sea fish with a bioluminescent glowing bulb—as well as grasshoppers. Famously, female grasshoppers are known to bite off the head of the male once they’ve finished mating; there’s no surviving that!
Why do females have longer lifespans?
Saying that females live longer implies that males have shorter lives. One plausible hypothesis is that males (rather than females) tend to compete for mates and food, meaning that they engage in fights and conflict far more than their female counterparts. The more you fight, the higher the likelihood of you dying early!
One way to prove this theory is through female kukri snakes. They are seen to be the defenders of their territory and their eggs, and are also required to fight over food. The females, in this case, showed decreased lifespans in comparison to males. After a natural disaster occurred that removed the turtle populations threatening their territories, the female snakes had no reason to be territorial and aggressive. These very same female kukri snakes then showed roughly the same survival rates as their male counterparts (Source).
Ultimately, based on this theory, the reason for the trend of females living longer than males is simple—males are more frequently aggressive in the wild because they must fight for mates more often than females must defend their eggs and territories.
This theory covers most birds, mammals and reptiles, including others with multiple mating partners (polygamous). Therefore, monogamous pairs (usually in birds) show reduced differences in longevity because the male also helps equally in raising the young, finding food and defending the nest with his partner.
Other popular theories
From an evolutionary standpoint, genetic information is more valuable than the actual body. As in most species in the animal world, the female is seen as the producer of offspring—the “propagator”, so to speak. Studies have found that the cell repair mechanism of females in most mammalian species functioned better and longer than in males (Source).
Evolution favors reproduction over an increased lifespan. The primary goal of life is simple—keep the species going. Everything else is secondary. In most cases, the female is responsible for this task, so she needs to be kept healthy. Her body will spend more energy on healing and preserving itself, as compared to her male counterpart. As a result, females live longer (Source).
Another major theory relates to higher testosterone, the male sex hormone, being the driving force for earlier mortality in males. The hormone has been linked to decreased immunity levels (Source).
On a genetic level, another possibility is that most mammalian males have just one X chromosome. This increases their susceptibility to sex-linked diseases against which females are generally protected since they have a second X chromosome to mask the deleterious effects of the first (Source).
There are too many theories… which one fits?
The exact reason for these differences cannot be pinpointed, because biology is not an exact science. Most likely, it is a combination of all these factors and more, including environmental and ecological conditions. The species of animal, its mating and feeding habits, and its relationship with other animals all play a role in determining its lifespan.
As with all things, there are exceptions to this female longevity trend, including some geese, babblers, woodpeckers and bats that show longer male lifespans. In any case, studies of sexual differences in lifespan for different species are said to be “incomplete at best”. More work must be done across all taxa of the animal kingdom in this regard if we want to fully understand this phenomenon of powerful and long-lived female creatures across the world.
- National Institutes Of Health (NIH) (Link 1)
- National Institutes Of Health (NIH) (Link 2)
- Our World In Data
- Stanford University