How Much Does Genetics Dictate a Person's Life Expectancy?

 

There are many factors that come into play when it comes to how long they will live for. According to a study done by Nicholette Zeliadt, "A person's life span is thought to be largely determined by the combined effects of genetic and environmental effects. Twin studies suggests genetics only accounts for approximately 20 to 30 of an individual's chance of surviving to age 85." Poor habits like a bad diet, drinking, or smoking make someone's fitness worse. The theory of exceptional longevity (EL) being common in family tree's makes it seem that life expectancy can be inherited amongst genetics. EL is when someone lives a decade past the average life expectancy of their generation, that tends to be common in families rather than sporadic. Where as genetics can become beneficial to a person's longevity, they can also lower someone's chance of a long life. Inheriting an unfavorable disease is just as possible as a favorable one is. 

Link: https://www.scientificamerican.com/article/genetic-factors-associated-with-increased-longevity-identified/#:~:text=A%20person's%20life%20span%20is,of%20surviving%20to%20age%2085.

Link: https://www.frontiersin.org/articles/10.3389/fgene.2012.00277/full

Life Expectancy Runs In Families, But Not By Genes

Calico Life Sciences is a development company that continues to research to learn much more about the biology of aging as their goal.  For this particular research, they used an open pedigree data from Ancestry.com, the website for Ancestry, the online genealogy resource.  Ancestry has the largest data set that they can use for their studies of longevity.  It is used to measure life span heritability.  Heritability gives us a quantitative value of a trait variation, such as life span, that are due to differences in genes.

It was thought that the estimated life span heritability was between 15 to 30 percent.  The Calico research team studied life span similarities from numerous pedigrees that involved a total of over 400 million people, connected by a parent-child or spouse-spouse relationship.  Initially, siblings and first cousins had heritability estimates no different from what was previously predicted.  However, spouses’ life spans were even more strongly correlated, likely not due to genetic factors but more so having a shared environment.  Even more unexpected was that remote relationship types, as far as a spouse’s sibling’s spouse, still had a similar life span, without being blood relatives or a shared environment.  What the researchers concluded was that assortative mating took place, meaning people tend to select partners with traits like their own.  For instance, wealthy people tend to marry other wealthy people, or tall people choose tall spouses.  This leads to the belief that life span is mainly controlled by genetics, when in actuality, life span heritability was calculated to not even surpass seven percent.

I previously hoped that scientists can discover so much more about the biology of aging through studying genetics.  But if genetics barely has anything to influence an individual’s life span, then alternative directions and paths need to be taken in order to find out the true answers on aging.

For additional information, refer to the original article.

For additional information, click the link of the journal of heritability estimates of human longevity.

What's the Longest Humans Can Live?

Jeanne Calment set the record for the longest living person after she died on August 4, 1997 at 122 years old. Humans have been progressively living for longer over the last few centuries, but it is likely that we have reached our limit, at about 115 years, according to Dr. Jan Vijg from Albert Einstein College of Medicine. Other experts agree with him, but some disagree strongly, basing their arguments on the fact that life expectancies have been increasing rapidly since the early 1900s. However, studies have been done which look at the growth of the population of a given age from year to year. For example, in France in the 1920s, 85 year olds were the fastest growing group of people. This trend shifted to even older people as the average life expectancy grew but about a decade ago, the peak stopped shifting. This is likely due to the stall in life expectancy. The International Database on Longevity also points to the same conclusion- people are not living as long as they used to decades ago, and besides the rare case like Jeanne Calment's, no one is living longer than about 115 years.

It is predicted that 115 will be the highest age that anyone reaches in the foreseeable future. It has been an ongoing argument for years whether or not there is a limit to lifespans, and because people have been steadily reaching the same age for decades now, it seems that there are only so many years that a body can live and work and continue repairing itself before it collapses.
I agree that there is a certain ceiling for age that humans can reach. The body is simply not able to continue repairing itself after a certain point. Because of the advancements in medicine and quality of life that have been improving over the past few centuries, life span has been increasing steadily, but at this point in time we have most likely reached the limit to how old we can get. 

DNA Strands at the End of Chromosomes Hints When We're Going to Die

A few days ago, an article was published explaining that biologist, Jason Alder, is starting to realize that the length of telomeres (DNA at the end of chromosomes) is correlated to each person's life span.   Besides hinting at the length of a life, telomeres also have the ability to hint if a specific individual has a higher chance of having bone marrow or liver failure.

When cells replicate, the DNA from the telomeres gets shorter and shorter.   When a chromosome runs out of DNA, the cell dies or becomes inactive.  Inactive cells typically develop into cancer.  However, by looking at the length of different individuals telomeres, a scientist would be able to estimate how long they have to live based off of how many more cell divisions exist.

Alder also found that the length of telomeres can be caused by a mutation of the TINF2 gene in an article that he co-authored.  The mutations from this same gene can also trigger different diseases.  Interestingly enough, the mutated genes can be passed from generation to generation.  This would cause future generations to have a lower life expectancy.  I think that finding out what could be the cause for shorter life spans is interesting.  I also think that it's dangerous because there could easily be a to extend life.  If extending telomeres becomes a popular trend; the life span of the population will be so much longer and the population will get much, much larger.