The analysis of genetic and behavioral data from the vast UK Biobank database finally reveals that the genes that enhance reproductive behaviors come at a cost.
Age Progression and the Impact of Genetic Generations
Aging is bothersome. You get wrinkles on your skin, slow down, forget things, and feel pain everywhere. Your joints creak and make noises. Evolution has achieved many amazing things; so how can we continue to age?
The antagonistic pleiotropy hypothesis suggests that your body breaks down when you are elderly to pay the price for reproductive success when you were young. If the same gene has different effects (called pleiotropy) at different times in life – if it enhances your chances of reproduction when you are young but is harmful in some way when you get older – then this gene will undergo positive selection and remain in the population because reproduction is so important.
It’s an appealing idea, and there is some anecdotal evidence for it, but it’s very difficult to prove it definitively and genetically – especially since reproductive traits and longevity are heavily influenced by environmental factors and life choices, in addition to genes. But the UK Biobank has made this proof possible. “An unprecedented opportunity”
UK Biobank Database
The UK Biobank contains complete generations of half a million British volunteers aged between 40 and 70 years. These generations were compiled with blood pressure, heart rate, grip strength, bone density, arterial stiffness, eyesight, height, weight, hip and waist measurements, location, education level, employment, medical records, dietary habits, exercise, smoking and drinking status, etc. Volunteers were recruited between 2006 and 2010, and information was collected until 2016. All of this information is accessible to accredited researchers worldwide.
The Genetic Influence on Longevity
One of those researchers is Jianzi Zhang, whose lab website states that “Zhang Lab is very interested in the relative roles of chance and necessity in evolution.” He used data from the UK Biobank to try to answer the following question: Are genetic generations affecting reproduction more likely to influence longevity than expected by chance? If so, is this correlation antagonistic? And do these generations that enhance reproduction also cause aging due to natural selection? The answers are yes, yes, and yes.
Reproductive fitness doesn’t just mean the number of children you have. To assess it, researchers also looked at genes associated with reproductive activities such as your age when you had your first child (curiously, this was only recorded for women), your age when you first had sex, and age at puberty and menopause. Because most people in the UK Biobank are still alive, researchers examined the genetic correlation of these factors with the age of their parents. Since they know the number of siblings each participant has, they can also search for correlations between parental reproduction and their age.
Genes vs. Environment
Most genetic sites that mediated the correlation between high reproduction and longevity were found in non-coding regions of genes. This means they do not change the proteins produced by the genes; rather, they change when and in what types of cells those proteins are produced. For example, one genetic variant is associated with younger age at first sexual intercourse and also with increased risk of melanoma and lung cancer later in life.
These genetic factors conflict with environmental influences, which have led to declining birth rates alongside increasing life expectancy since the mid-20th century. The authors note that these extended timeframes are part of what allowed them to find evidence of antagonistic pleiotropy in the genetic data.
So,
The more children you have, the shorter your life span will be. Not because your kids will drive you crazy and spend all your money, although they probably will. It’s just the price you pay for them.
Source: Science Advances, 2023. DOI: 10.1126/sciadv.adh4990
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