Telomere

Telomere shortening is associated with aging, mortality and aging-related diseases. Normal aging is associated with telomere shortening in both humans and mice, and studies on genetically modified animal models suggest causal links between telomere erosion and aging.^[26] However, it is not known whether short telomeres are just a symptom of senescence or if they themselves contribute to the progression of the aging process.^[27]

The age of a father plays a role in the length of a child’s telomeres, which has evolutionary implications. Although leukocyte telomeres shorten with age, sperm telomeres lengthen with age. Shorter telomeres are theorized to impose lower energy costs (due to less replication) but also have immune system-related and other aging- and disease-related costs, so the effect of paternal age on telomere length might be an adaptation to increase the chances that the child will be fit for the environment they’re born into.^[28][29]

The phenomenon of limited cellular division was first observed by Leonard Hayflick, and is now referred to as the Hayflick limit.^[32][33] Significant discoveries were subsequently made by a group of scientists organized at Geron Corporation by Geron's founder Michael D. West, that tied telomere shortening with the Hayflick limit.^[34] The cloning of the catalytic component of telomerase enabled experiments to test whether the expression of telomerase at levels sufficient to prevent telomere shortening was capable of immortalizing human cells. Telomerase was demonstrated in a 1998 publication in Science to be capable of extending cell lifespan, and now is well-recognized as capable of immortalizing human somatic cells.^[35]

Source: https://en.wikipedia.org/wiki/Telomere#Lengthening