Middle Age

A Natural History

David Bainbridge

• Publisher: Portobello Books
• Year: 2020
• Print ISBN: 9781846272684
• eBook ISBN: 9781846274367
• Topic: Psychology
• Subtopic: Developmental Psychology
• Index: Psychology

"There's lots of good news for the middle aged…A very jolly book with clear scientific explanations."— The Telegraph
 
David Bainbridge is a vet with a particular interest in evolutionary zoology—and he has just turned forty. As well as the usual concerns about greying hair, failing eyesight, and goldfish levels of forgetfulness, he finds himself pondering some bigger questions: have I come to the end of my productive life as a human being? And what I am now for?
 
By looking afresh at the latest research from the fields of anthropology, neuroscience, psychology, and reproductive biology, it seems that the answers are surprisingly, reassuringly encouraging. In clear, engaging and amiable prose, Bainbridge explains the science behind the physical, mental and emotional changes men and women experience between the ages of 40 and 60, and reveals the evolutionary—and personal—benefits of middle age, which is unique to human beings and helps to explain the extraordinary success of our species. Middle Age will change the way you think about midlife, and help turn the crisis into a cause for celebration.
 
"Bainbridge's zoological examination of the human animal results in a study that is full of surprises...Heartening."— Sunday Times
"Thought-provoking. [It] should certainly shed some new light on one's own potbellied or menopausal mid-life crisis...Fascinating."— Evening Standard

PART I

FROM SAVANNA TO SUBURBIA:

Why Middle Age Has Never Been About Growing Old

I believe that our Heavenly Father invented man
because he was disappointed in the monkey.

Mark Twain, autobiography, 1924

1. What makes middle-aged people?

To understand middle age, we must start with some basic questions. So many aspects of life converge to create the phenomenon we call middle age, that at first sight it may seem an insuperably large topic. In the fifth and sixth decades of our lives we change physically, intellectually, sexually, emotionally and socially in ways which are interwoven, complex and profound. Also, middle age differs dramatically between individuals, sexes and cultures. How are we ever to comprehend this bubbling ferment of change and variability?

We have to start somewhere, so I will start with a deceptively simple question: what processes lead to the creation of a middle-aged human? And as we will see in this first chapter, to answer this question we must understand three things: genes, development and evolution.

I

Genes come first.

Forming any sort of animal requires three things: energy, chemicals and information. In fact, making something as wonderful as a middle-aged person requires a very great deal of energy, chemicals and information. However, we are not going to worry about the energy and the chemicals – we acquire those by eating and breathing just like any other animal, so it is not they which make middle-aged humans special. Instead we are going to concentrate on the information, because that is the interesting bit. Only humans have the necessary information to make middle-aged people.

A surprisingly large amount of the information needed to make a middle-aged person is stored in our genes – not all the information, but most of it. In the central nucleus of almost every cell in your body are forty-six stringy chromosomes, each containing extremely long chain-like molecules called deoxyribonucleic acid, or DNA. DNA has several properties which make it very good for storing the information required to make an animal. First of all, it is inherently stable and resilient, and we also have mechanisms to repair it so that it lasts even longer. Second, its famous ‘double-helix’ structure means that one DNA molecule can untwine and reform into two DNA molecules pretty much identical to the original – and this is what happens when cells divide. Third, DNA can be deliberately cut and spliced back together, and this is what happens when two individuals are manufacturing eggs and sperm with a view to making babies.

The fourth and final useful property of DNA is that it can be used to make things. In each human cell there are roughly 23,000 stretches of DNA which can be put to creative use, and we call these stretches ‘genes’. The DNA chains which constitute these genes are not uniform along their length; instead they are formed by the joining together of four different elements (called A, C, G and T) and those blocks may be threaded together in any order like red, green, blue and yellow beads on a string. For example, a gene which is used to make type I collagen (a protein which makes up much of the mass of the human body, helps stop middle-aged people sagging too much, and is often mentioned in adverts for anti-ageing cream), starts with its building blocks in the order: ATG TTC AGC TTT GTG GAC CTC CGG CTC CTG …

This may not look like a very promising start, but bear with me. This DNA ‘genetic’ sequence is only useful because there exists a complex machinery in every cell which knows that the sequence is a code. Special molecules continually decrypt this gene code to make molecules (usually proteins) which do everything to make the cell work. Genes can make all sorts of proteins – proteins that chop chemicals up or join them together, proteins that allow things to flow in and out of cells, proteins that cause movement, or proteins like collagen which provide structural support. In fact, almost everything that goes on inside your body is the result of the activity of the molecules produced by those 23,000 genes.

All these codes and products may sound arcane, but it is important to realize that these genetic codes are all the information that most animals ever get. If you hatch from an egg and wriggle away with no parental care at all, the only thing you have to steer you through life is the information contained in the genes you inherited from your parents. Those genes are the sum total of the guidance you are given to form yourself, grow, behave and breed. Without genes, we would be nothing.

As we will soon see, humans get additional information to that which is encoded in their genes, but not much. It is remarkable that only 23,000 coded instructions constitute most of what is required to generate, operate and maintain a middle-aged person. In fact, when the human genes were first totted up, biologists were shocked to discover that this number was so small. Many cars have more components than that, and they cannot do a fraction of the things a person can do. When you consider that roughly thirty of those genes are required to make all the different types of collagen, and over a thousand are set aside for detecting smells, you can see that there will be surprisingly few genes left to coordinate complex things like making babies and orchestrating a midlife crisis.

II

So much for genes. Now for development.

Every so often I am asked to give talks about biology to engineers and architects at my university. There are many justifications I use to claim to them that ‘my machines’ of flesh and blood are much cleverer than ‘their machines’ of steel and glass, but usually the most convincing is that my biological machines have to develop and grow autonomously, all the while still functioning as a living organism. For example, there is no stage in human development when our constituent parts can lie scattered and idle on a workbench, waiting for some benevolent constructor to put them together. Instead, humans and animals must self-assemble, and they must remain functional throughout this self-assembly.

In fact, this self-assembly is the most bewilderingly wonderful thing that our 23,000 genetic instructions coordinate. It seems such a demanding feat that we suspect it is the primary function of many of those 23,000. As a result, developmental biology is a big part of modern biological science, with thousands of scientists around the world labouring to identify the processes involved as a single-celled fertilized egg converts itself into a large, fully functioning, complex adult animal. Once again, it turns out that the vast majority of the information – the instructions – required to make a mature human being is contained in the simple A-C-G-T code of the genes. Developing animals are awash with cascades of genetic activity, as individual gene products switch on other genes, which in turn fire up yet more genes. This array of gene products then produces hands, ears, kidneys and hearts by inducing cells to proliferate, migrate, cooperate, specialize or die in very complex configurations.

Modern developmental biology has shown us amazing things. For example, some genes are so useful in forming bodies that they have been used repeatedly throughout evolution. Because of this, many genes are common to the development of humans, mice, fish, flies and worms. It is as if we all share a common genetic toolbox with molecular spanners and protein screwdrivers which can be turned to almost any purpose. Indeed, many of these genes are so useful that they can be reused many times during the creation of a single body – for example, a single gene may be used to create things as diverse as brain, liver, bone and testicle. This reuse of the same genes for different purposes is probably how we can get away with having as few as 23,000 genes, but it also means that these multi-purpose genes must be used very carefully. Otherwise you might end up with testicles in your skull.

All these developmental discoveries have changed the way we think about ourselves, but there are two important points I would like to make about how genes control the construction of a human body. These points are irrelevant for most of developmental biology, but they are crucial for us because we are interested in middle age, and middle age is special.

First, we must not be misled by the fact that most developmental biology has focused on what happens before we are born. This focus is entirely understandable, because the science was driven by an urge to find out how something as spectacular as a baby can be forged from something as insignificant as a fertilized egg. However, development is certainly not only about embryos and fetuses: after we are born there is still a great deal of developing left to be done. This post-natal development is just as crucial and gene-driven as the pre-natal kind, even though it occurs at a more leisurely pace. For example, for the first two years of life the brain keeps growing at the same rate that it grew before birth. And, after a pause, the reproductive organs suddenly start a rapid process of development in the early teens. The limb bones also keep growing in fits and starts throughout the first two decades of life. Yet even that is not the end of development. One of the central ideas of this book is that the developmental programme does not stop at birth, or puberty, or skeletal maturity. The genetic ‘clock of life’ just keeps on ticking and people keep on changing far into adulthood. We will see that there is a positive, active series of genetic events which continues long enough to cause things like the menopause and middle-aged spread. A striking example of this is the distribution of male body hair, which changes and develops continuously throughout the first sixty years of life. Changes as specific and distinctive as this simply cannot be explained any other way, and certainly not as part of a process of uncontrolled deterioration and ageing. A middle-aged human must continue to develop in much the same way that a human fetus develops – otherwise middle-aged people would just look like tatty twenty-year-olds. You may be grown up by forty, but you have not finished developing.

The second point I want to emphasize about the development of middle-aged people is an unusual feature of the human brain. The brain plays a critical role because we are a very intelligent and very social species. However, it has one strange feature – it responds to change in other parts of the body in a manner quite unlike any other organ. Let us take social and sexual behaviour in middle-aged women as an example. Obviously middle-aged women think and behave differently from younger women, and we can expect this to be caused partly by genetic and cellular changes in the brain. However, there is another force affecting how such women behave: their brain is all too aware of the changes going on in their own body. Unlike other organs, the brain reacts and responds to its subjective perception of the body which it inhabits – it is self-aware. Whether you look young and beautiful or old and haggard will have a big effect on your self-image, attitudes and thought processes. People are all too aware of the importance of their place in the human social world, and because of this, their perceptions of themselves continually mould the way they think. Of course, whether you actually are old and haggard is itself largely controlled by age and genes, but in this context age and genes are not affecting your brain directly. Instead they are affecting the brain indirectly by changing the body in which that brain finds itself imprisoned.

III

There is one more thing we need to consider if we are to understand the origins of middle age: evolution.

The genes that make today’s middle-aged humans are the genes we have inherited from our ancestors – generation after generation of humans, proto-humans and even pre-humans trying to make their way in the world, sometimes failing and sometimes succeeding. By the early eighteenth century many zoologists had concluded that animal species change over time, and sometimes even split into multiple descendant species. Because some species look so similar to others, it was hard to believe that each was formed in a separate act of divine creation. Instead, some animals just appeared to be subtly modified versions of others. This process of gradual change and multiplication of animal types over time was given a name – ‘evolution’, a term stolen from eighteenth-century linguisticians who had used it to explain how human languages have changed over time.

It was two British naturalists, Alfred Russel Wallace and Charles Darwin, who first proposed a convincing mechanism by which evolution might take place, and we now call their ingenious theory ‘natural selection’. For centuries it had been noticed that animal populations vary – any species of animal contains large individuals, small individuals, fast individuals, slow individuals. And any decent stockbreeder knew that if individual animals were selectively bred, there would be a good chance that their offspring would inherit their parents’ characteristics. In other words, animal populations could be seen as seething masses of variations which can by some physical (that is, not spiritual) means be passed down the generations. At the time, no one fully understood what these physical means were, but we now know them as genes.

Wallace and Darwin realized that heritable traits provide a means by which animal species can change over time and gathered a great deal of evidence to support their theory. The exact process of natural selection is very important for understanding how humans evolved middle age. According to natural selection, if certain traits are beneficial to an animal and help it to produce many successful offspring, then the genes which produce those traits will survive and be propagated in future. Over the generations this process happens again and again, with genes which promote successful reproduction accumulating while genes which do not promote it are lost for ever. As a species’ environment changes, so the traits required to help it breed in that environment change too, with the miraculous result that the animals themselves slowly alter over the millennia. Thus, animals adapt to their changing environment, and this goes a long way towards explaining how evolution occurs.

This book is entirely based on the premise that human middle age results from millions of years of evolution of genes. Because of this, there are some issues which I should address straight away.

The first is the question of evidence: how much proof do we have that evolution by natural selection actually takes place? One line of evidence is copious, and this is the observation that the animals alive today and the fossils we dig out of the ground certainly look like products of extremely long periods of evolution. However, some would say that this after-the-event evidence is not good enough, so biologists have tried to observe evolution actually taking place. Because evolution happens quite slowly this is not an easy thing to do, but it is possible. Scientists have watched rapidly evolving organisms such as microbes change over the generations, and they have also observed evolutionary change in larger animals when they are placed under strong natural selection pressures – such as lizards being introduced to new islands. It has even been possible to observe evolution in stressed human populations, as in the rapid development of community-wide genetic resistance to the devastating spongiform brain disease kuru (‘laughing death’) in cannibalistic New Guinea tribes. All in all, the evidence for the theory of evolution by natural selection is pretty good, and human evolution is not an exception.

The second issue is an element of evolutionary science which has caused a great deal of controversy: the evolution of our psychology and behaviour. The way we think is such an important part of our lives that some scientists proposed that our psychology has evolved to its present state in exactly the same way that our physical attributes have evolved. Thus was an entire new field of science born: evolutionary psychology. Evolutionary psychology has its critics but I should come clean and say that I am not one of them: I consider it to be a reasonable approach to the origins of human behaviour – and certainly not just a way of confabulating ‘just-so’ stories of why humans ended up behaving the way they do. After all, why should genes which make us think in ways which promote our success not also be bred into us by natural selection?

The third and final thing to mention about the genetic evolution of middle age is a paradox relating to the central importance of breeding in the theory of natural selection. Put simply, if natural selection involves the propagation of genes which help us breed, then where does this leave people who are no longer breeding? For example, does Darwinism mean that only children and young adults are naturally selected? Are post-reproductive, middle-aged people evolutionarily irrelevant? As we will see, this is an extremely important issue for us to confront in this book. If people over forty are not subject to natural selection, then this would mean they did not really evolve at all. And this would be extremely awkward because evolution of middle-aged people is the whole point of this book.

I hope this brief tour of the basic genetic processes which created middle-aged humans, and which still create them today, has given you some hints as to why they are so exceptional. But this glimpse into our evolutionary origins leaves us with yet more big questions to answer. When in human history did middle age – and the panoply of quirky wonders it bestows on us – actually appear? Why does human middle age evolve if it takes place after most of us ha...

Table of contents

• Cover
• Title Page
• Table of Contents
• Epigraph
• Introduction : A New Story of Middle Age
• PART I : FROM SAVANNA TO SUBURBIA: Why Middle Age Has Never Been About Growing Old
• PART II : STILL CRAZY AFTER ALL THESE YEARS: The Triumph of the Middle-Aged Mind
• PART III : OLDER AND BOLDER:Romance, Love, Sex, Babies and Life After Forty
• ABOUT THE AUTHOR
• ACKNOWLEDGEMENTS
• SELECTED BIBLIOGRAPHY
• Index
• A, B, C
• D, E, F
• G, H, I
• J, K, L
• M, N, O
• P, Q, R
• S, T, U
• V, W, X
• Also by this author
• Copyright