The analysis of genomic and behavioral data from the UK Biobank finally shows that the genes that enhance reproductive behaviors come at a cost.
Aging and the Impact of Genetic Generations
Aging is a problem. You get signs on your skin, you move slower, you forget things, and you feel pain in everything. Your joints crack and explode. Evolution has achieved many amazing things; how can we continue to withstand aging?
The antagonistic pleiotropy hypothesis posits that your body breaks down when you’re old to pay the price for reproductive success when you’re young. If the same gene has different effects (called pleiotropy) at different times in life – if it enhances your chances of reproduction when you’re young but is harmful in some way when you grow old – then this gene will be subject to positive selection and remain in the population because reproduction is incredibly important.
It’s an appealing idea, and there’s some anecdotal evidence for it, but it’s very difficult to prove conclusively genetically – especially since reproductive traits and lifespan are heavily influenced by environmental factors and life choices, in addition to genetics. But the UK Biobank provided this proof. “An unprecedented opportunity”
The UK Biobank and Genetic Study
The UK Biobank contains full generations of half a million British volunteers aged 40 to 70. These generations are compiled with blood pressure, heart rate, grip strength, bone density, arterial stiffness, vision, height, weight, hip and waist measurements, location, educational level, employment, medical records, dietary habits, exercise, and smoking and drinking status, etc. Volunteers were recruited between 2006 and 2010, and information was collected until 2016. All this information is accessible to approved researchers around the world.
One of these researchers is Jianzi Zhang, whose lab homepage states that “Zhang Lab is greatly 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 the genetic generations influencing reproduction more likely to impact lifespan than expected by chance? If so, is this correlation adverse? And do these generations that enhance reproduction but also cause aging favorably act through natural selection? The answers are yes, yes, and yes.
Genetic Generations and Environment
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 (strangely, this was only recorded for women), your age when you first had sex, and the age of menstruation and menopause. Since most people in the UK Biobank are still alive, researchers examined the genetic correlation of these things with the age of their parents. Since they know the number of siblings for each participant, they could also look for correlations between parental reproduction and lifespan.
Most of the genetic sites mediating the link between high reproduction and shorter lifespan occurred in non-coding regions of the genes. This means they do not change the proteins produced by genes; rather, they change when and in what types of cells those proteins are produced. For example, one genetic strain is associated with a younger age at first sexual intercourse and also with an 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 lifespan since the mid-20th century. The authors note that these extended time frames are part of what allowed them to find evidence of antagonistic pleiotropy in genomic data.
So,
The more offspring you have, the shorter your hypothetical lifespan. Not because your children 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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