Some people believe that, unlike us, “cavemen” were in sync with their environment. Why? Because “We’re fat and unfi t, we have high blood pressure, and we suff er from ailments that we suspect our ancestors never worried about…” But is this because we are stuck in a modern environment with ancient bodies and genes? In her book Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live, Marlene Zuk questions this dogma. She shows that evolutionary changes have enabled us to eat and digest a wider range of foods than our ancestors could, but our overindulgence of energy-dense and easily available foods and sloth are contributing to the so-called diseases of civilisation.
Zuk states that evolution is continuous, “can be fast, slow, or in-between”, does not have a purpose, and does not necessarily mean progress. It can occur with or without natural selection, which can be classically thought of as the “winnowing out of genetic variants”: organisms and genes that are most suited to their environment survive and reproduce. She provides many examples of evolution and claims that there has never been a “seamless match” between any species and the environment. The belief that human beings stopped evolving, or are doing so incrementally over 100 000s of years, is just a fallacy.
An example of the many evolutionary changes in human beings is the appearance of blue eyes through a random genetic change about 6000–10 000 years ago. The ability to consume diverse foods, including dairy products and starchy foods, is another example. Lactase persistence after weaning is an evolutionary change that arose through natural selection, enabling about 35% of the human population, clustered in northern Europe and parts of Africa and the Middle East, to remain lactose tolerant in adulthood. Zuk explains that this change occurred about the time Homo sapiens started domesticating cattle—at least 7000 years ago. Milk consumption has benefi ts: it is a source of nutrition (calcium, protein, and sugar), and, for people living in deserts, can be a vital, uncontaminated source of liquid.
Another example of a food-related evolutionary change in human beings is the adaptation to eat starchy foods. Amylase, an enzyme released from the salivary glands and the pancreas, enables the digestion of starch. The amylase gene is “prone to duplication”, but this duplication does not happen during our lifetimes—instead, we inherit the number of copies of the gene from our parents. As a result of natural selection, individuals whose diets contain high amounts of starchy foods have “multiple copies” of the amylase gene compared with those whose diets are rich in meat and fish. Zuk states that domestication of cereal crops (eg, barley and rice) probably happened after natural selection for the ability to digest starch.
All of this is bad news for people who want to counter the various eff ects of the modern lifestyles on their health, and have opted to follow the paleo diet. Unfortunately for them, through evolution, neither we nor the foods that we eat have remained the same since “caveman” times. We are behaviourally and physiologically very diff erent from our ancestors: “The caveman wouldn’t just fi nd our modern cuisine foreign; the microbes inside of us…would be at least as strange”. And Zuk explains that there is no such thing as a natural diet for human beings because we “ate too many diff erent foods in the past, and have adapted to too many new ones”. The belief that we should adjust our diets to conform to a “caveman” ideal, therefore, seems somewhat misguided.
Zuk also issues a warning for modern human beings “that a life of sloth with a diet of junk food isn’t doing us any favors”. She explains that we evolved under conditions of a feast–famine cycle. Hence, a sedentary state sends signals (Zuk does not say what these are) to the genes that there is about to be a famine, so the body makes the best use of resources for the short term. A sedentary lifestyle alters metabolism to favour weight gain and can cause adverse changes—eg, in concentrations of triglycerides, one of the risk factors for heart disease. And because short periods of intense exercise will not be enough to stave off these problems, Zuk stresses the need to move around more to avoid increases in waistlines and blood pressure, and problems with blood sugar concentrations. Other harmful eff ects of being “couch potatoes” include increased rates of anxiety, depression, and mortality.
Although diabetes type 2 can afflict individuals irrespective of ethnic origin, Zuk notes that the fastest increase in prevalence has been in people of non-European descent. She proposes that these individuals have “thrifty genes” that allow the effi cient use of sugar and storage of fat, enabling survival during famine. But when food is always abundant, these genes “promote hyperglycemia and problems with insulin regulation”.
Zuk provides nice metaphorical food for thought about evolution. After reading her book, I wonder whether our ancestors actually felt in sync with their environment. Perhaps they too pined for a past era in which they assumed their forebears had been content with their lives. Or maybe “cavemen” were too preoccupied about their future and were contemplating ways to domesticate ungulates (mammals with hooves) when they were not busy pursuing their food. With scant evidence, who can really say?
Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live Marlene Zuk, W W Norton and Company, 2013. Pp 328. ISBN 978-0-393-08137-4