Men become less fertile with age, but the same isn’t true for all animals: Study

We understand it as humans find it. Getting pregnant is more difficult As they grow up. But Our recent studywho analyzed data from 157 animal species, found that male reproductive age appears to be much less common in other male animals.

With fertility in men Worldwide declineUnderstanding aging Sperm Other animals may provide new insights into our own fertility.

Human fertility declines with age because older people have fewer sperm and eggs. Worse or less than the number of young people. Reproducing at an older age not only affects your fertility, it can also Reduce fertilitysurvival rates and the physical and cognitive performance of your unborn babies.

Humans compared to other animals

Humans Live long enough As we did just a century ago. This Recent, rapid expansion One reason for our longevity may be that humans reproduce at a faster rate than other animals. Our reproductive aging rates have not yet slowed to match our longevity.

Animals may also face greater evolutionary pressure to maximize their reproductive potential at each age, since most animals reproduce throughout their lives. But this is not the case with humans. We rarely Present again In our last life.

In addition, we have Few children Compared to our ancestors. It makes it harder for him. Natural selection To select genes that improve human reproduction due to low variation in population fecundity.

Women vs Men

In many species males and females reach reproductive age at different rates.

For example, in red wolves, male reproductive success declines with age but this does not For females, however, female kelp show a strong decline in fertility with age. Compared to men. Despite the fact that human females live longer than males, they become infertile. Before menand go through menopause.

In some species, including humans, where females help raise their offspring (such as humans and whales), females remain Far ahead of age of reproduction. one Evolutionary explanation This is because older women can better pass on their genes by helping their relatives to survive and grow younger than by reproducing themselves.

There are some hypotheses that try to explain them. Gender differences in reproductive age.

Sperm are produced continuously in males, but eggs in many species, Including humans, are born early in women’s lives. It can lead to egg Accumulate more damage Because sperm are stored longer in older women than in older men.

Another hypothesis suggests that sperm DNA may make men live longer. More collection Mutations compared to egg DNA. Sperm have a weaker DNA repair machinery than eggs, causing males to have this condition. Transfer more mutations. compared to females with increasing age for the next generation, a pattern seen in vertebrates.

The sexes also face different environmental stressors. For example, in many mammals, males, but not females, withdraw from the family group as adults. This type of environmental pressure leads to differences in the strategies that males and females use to pass on their genes, which can differentiate them. The rate of reproductive aging between the sexes.

Patterns of reproductive aging in animals.

In our study, we showed that reproductive aging rates in men Widely different In the animal kingdom. We found that invertebrates such as crustaceans and insects have some of the lowest rates of reproductive lifespan, compared to laboratory mice which have somewhat faster rates. In general, however, male animals showed few signs of age-related decline in their ejaculatory characteristics (such as sperm quality and quantity).

We also found that different ejaculate characteristics, such as sperm viability, number, motility or speed, age at different rates.

In species that grow throughout their lives, such as some fishes and crustaceans, older animals are less likely to die and have larger gonads than young males. It can cause old men. In such species Older men ejaculate more than younger men

In animals such as the lab rat, which have some genetic lines selected for rapid aging, reproductive aging was universal across ejaculatory traits. Lab rats are typically kept in highly controlled environments where aging is easier to detect—due to fewer confounding effects that can mask aging. This suggests that the great variation in male reproductive age between different species may be due to their environment.

We also discovered that closely related species showed similar rates of ejaculate decline with age, suggesting that aging is also shaped by the animals’ evolutionary history.

Some of the patterns we mention above also reflect methodological differences between studies. For example, when the study treated male animals as virgins, older males could. High sperm count Compared to younger men, older men produce larger ejaculates.

Additionally, studies that sampled only young to middle-aged men showed an increase in sperm quality and quantity with age, compared to studies that sampled middle-aged to older men. , suggesting that fertility typically peaks around middle age in male animals.

Increasing reproductive age

Reproductive age is because as people get older, they have more sperm and eggs. Accumulate damage. Organisms have evolved to reproduce earlier in life rather than older, leading to a Weakness of natural selection Eliminating defective genes that are expressed in older but younger organisms, in turn promotes aging.

However, there are opposing forces that determine whether older individuals will pass on more copies of their genes to successive generations than younger animals, and reproductive aging is only one process that determines this.

An alternative hypothesis That is, parents who conceive at an older age have more gene variants for longevity that can benefit their offspring. This can lead to long-lived offspring from older pregnant parents. However, evidence for this hypothesis is still limited.

Although most scientists agree that at least some reproductive traits decline with age, biologists are still unraveling the exact mechanisms and evolutionary causes of these declines. But by looking to other species to research the drivers of reproductive aging, we can understand and perhaps even try to reverse our own reproductive decline with age.

This article has been republished. Conversation Under Creative Commons License. read Original article.