According to a news release yesterday; “TOKYO — Japanese people are living longer than ever, with the average life expectancy now 86.05 years for women and 79.29 years for men, the health ministry said Thursday. Japanese women extended their life expectancy by almost 22 days in 2008 from the previous year, while men added another 37 days, the ministry said.”
It seems like an immense increase in lifespan to happen in just one year. It is interesting to ask how could this happen. The usual theories are related to improvements in public health and nutrition: changes that happened 70-90 years ago that affected the survival rate of infants, public sanitation systems, less air and water pollution, better balanced diets, improvements in the Japanese health care system and more public awareness about health. I speculate here that something else more profound could also be involved – physical evolution of our species.
First I want to comment that the trend to longer life expectancy has been going on for many centuries now and has been happening in all developed countries. This table provides government statistics for “Life expectancy at birth, at 65 years of age, and at 75 years of age, by race and sex: United States, selected years 1900–2005.” All the numbers have been going up every year. A woman born in 1900 could expect to live 48.3 years; a woman born in 2005 can expect to live 80.4 years – a 66% increase. In Germany life expectancy at birth increased from 78.42 years in 2003 to 79.1 years in 2008(ref). The trend of increasing expectancy has been a very long one. This Table suggest that average life expectancy at birth in Medieval Britain was 20-30 years, in the early 20th century 30-40 years. This Table from the CIA World Factbook lists 2008 life expectancy at birth for 191 countries. At the top of the list is Macau with 84.38 combined male-female life expectancy at birth and at the bottom is Swaziland with 39.6 years combined life expectancy. The US ranks 45th on the list with 78.06 years. At the same time as life expectancy has increased there have been other shifts in average human body characteristics, such a towards greater height, particularly in advanced countries(ref).
My speculation is that human cultural evolution is leading to species evolution via epigenomic modifications in inheritable DNA that makes for longer longevity, and that this process is ongoing right now.. Specifically:
· As human industrial and post-industrial societies become more and more complex it takes longer and longer for young people to achieve the education and skills for them to become fully-functioning members of society. In Neolithic societies, at the age of about 15 children could start taking full adult responsibilities for hunting and gathering, bearing children and taking on the roles required for society to work. Nowadays, if a young person is pursuing a professional path, about twice as many years are required before that person is a fully-functioning doctor, lawyer, or other skilled professional. Instead of starting to have children at 15-16, the tendency in advanced countries now is for childbearing to be postponed until women are in their 30s or 40s(ref).
· While there are clearly class differences, the individual and societal investment required to bring young people up to speed has been growing and in the US may be nearing a half-million dollars for advanced professionals like doctors, lawyers, scientists and diplomats. While few finished high school a century ago, yesterday President Obama advocated that everyone should be provided at least a 2-year college education. Everything connected with full social maturation takes longer, is more complex and is more expensive
· From a viewpoint of simple cultural economics, it makes sense that this greatly expanded investment in initial maturation of individuals be accompanied by a much longer productive lifespan over which that investment is amortized.
In other words, arguing purely from an evolutionary viewpoint, it would make excellent sense for cultural evolution to induce species evolution so that people live longer. That is exactly what has been happening, but the exact mechanisms involved are unclear. There are probably several mechanisms at work including advances in public health knowledge and developments such as decline in cigarette smoking. Another mechanism may be greater dissemination of knowledge as to what makes for health and longevity, this blog playing a tiny part.
My speculation is that, in addition, inheritable epigenomic changes are happening in our DNA that are leading to greater longevity. That is, our genes themselves are not being changed but that there are modifications in our histone acetylation and DNA methylation patterns and other chromatin changes that on the whole help us live longer.
The general process of epigenomic modification is described in my February blog entry Epigenetics, Epigenomics and Aging. My speculation is feasible, given what we know about epigenomics. In fact, as I have speculated before, aging itself may largely be an epigenomic phenomenon. However, my speculation remains a speculation for now because I cannot say how and when longevity-promoting epigenomic reprogramming is taking place. For a possible hint, see also my previous blog post Longevity Genes and Two Fantasies. See also this reference for how hormonal mechanisms may affect longevity genes via epigenomic modifications.
