Human males tend to become less fertile as they age, but this is not the case for many other male animals, according to a new study that analyzed data from 157 animal species. The study, published in the journal Nature Communications, suggests that male fertility aging is influenced by factors such as longevity, life history and evolutionary pressures.
Male Fertility Declines With Age Due to Multiple Factors
It is well-known that humans find it more difficult to conceive as they grow older. This is because sperm and eggs of older people are more deteriorated or fewer in number than those of young people. Reproducing at an older age not only affects one’s fertility, but can also reduce the fertility, survival rate and physical and cognitive performance of the offspring.
Human fertility declines with age because of several reasons, such as:
- Longevity: Humans live considerably longer than we did just a century ago. This recent, rapid extension in our longevity might be one reason why humans reproductively age at faster rates than other animals. Our reproductive aging rate hasn’t slowed down yet to match our longer lifespans.
- Life history: Humans rarely reproduce in their late life. Additionally, we have fewer offspring compared to our ancestors. This makes it harder for natural selection to select genes that improve human reproduction due to less variation in the population’s fecundity.
- Sperm production: Sperm are continuously produced in males, but eggs in many species, including humans, are produced early in the life of females. This might lead eggs to accumulate more damage due to being stored for longer durations inside older females than sperm are stored in old males.
- DNA repair: Sperm have poorer DNA repair machinery than eggs, causing males to pass on more mutations to the next generation than females with advancing age, a pattern observed across vertebrate animals.
Male Reproductive Aging Is Less Common in Other Animals Due to Evolutionary Pressures
The researchers of the new study collected data on reproductive success and lifespan from 157 animal species, including mammals, birds, reptiles, amphibians and fish. They found that male reproductive aging seems to be a lot less common in other male animals than in human males.
The study found that only 42% of the animal species showed evidence of male reproductive aging, compared to 100% of the human populations. Moreover, the rate of decline in male fertility was much slower in other animals than in humans.
The study also found that male reproductive aging was more likely to occur in species that had longer lifespans, shorter reproductive periods and lower fecundity. These factors might reduce the evolutionary pressure to maintain high reproductive performance at older ages.
The study suggests that animals might face greater evolutionary pressure to maximize their reproductive potential at all ages, because most animals reproduce throughout their lives. But this isn’t the case for humans.
Implications for Human Fertility and Health: What Can We Learn from Other Animals?
The study provides new insights into the causes and consequences of human reproductive aging. It also highlights the need for more research on how aging affects sperm quality and function in different animal species.
The study also has implications for human fertility and health. As men get older, the quality of their sperm can decline, leading to lower chances of conception and higher risks of genetic abnormalities, erectile dysfunction and changes in the reproductive organs and tissues.
Therefore, it is important for men who want to have children later in life to be aware of these potential challenges and seek medical advice if needed. It is also advisable for men to adopt healthy lifestyle habits, such as avoiding smoking, alcohol and stress, eating a balanced diet and exercising regularly, to improve their fertility and overall well-being.
Additionally, men can learn from other animals that have higher fertility at older ages. For example, some animals have mechanisms that protect their sperm from oxidative stress or DNA damage, such as antioxidants or telomerase enzymes. Others have adaptations that increase their mating success or sperm competition, such as larger testes or longer copulation duration. These strategies might inspire new ways to enhance human male fertility aging.
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