Modern bodies: Our 10,000-year makeover

[Albion]

Civilised living has transformed our bodies, from deep within our bones to the tips of our fingers

IN A basement storeroom at the University of Zurich in Switzerland, rows of cardboard boxes are stacked tidily on metal shelves. Although they are stamped with the logo of a banana import company, they contain, not fruit, but something more macabre.

Inside are the heads of two Egyptian mummies and bits of ancient bog bodies. More recent remains include bones from a medieval graveyard, and others from Swiss citizens who died in the early 20th century.
Some of the body parts bear marks of exotic or violent rituals: there are traces of gold leaf around one of the mummies' eyes, for example. Others show the ravages of diseases that have long since been eradicated. In this plain, windowless room lie the remains of 2000 individuals, all told.

The collection is overseen by anatomist Frank Rühli, who wants to reconstruct the people to whom they once belonged. He is discovering how the human body has changed over the last few thousand years, to chart how civilisation is resculpting our bodies. The modern western lifestyle continues to change not only our waistline but also our height, muscles, bones, blood vessels and hormones.

Some of those transformations could be genetic in origin, examples of recent microevolution in action. But there is reason to suspect that others are temporary changes wrought throughout our lives that would melt away if we returned to a Stone Age environment. The complex interplay of nature and nurture is hard to disentangle, but the sheer breadth and scale of the changes show the ease with which the human body can adapt to new habitats over short timescales.

Discovering how those adaptations are making us more vulnerable to certain diseases and less so to others is an important facet of evolutionary or Darwinian medicine, an emerging specialty that views health and disease through the lens of evolutionary theory. Last October, the university opened a Centre for Evolutionary Medicine with Rühli at its head. This approach sheds light on many common ailments that have arisen because our modern western lifestyle is so different from the one we evolved to suit, says Rühli.

Anatomically modern humans are thought to have arrived on the scene around 200,000 years ago. They lived as hunter-gatherers in small nomadic groups until around 10,000 years ago, when the advent of farming led to permanent settlements and, in fits and starts, the long slog to civilisation.

Ancient remains

The idea that evolution could have been taking place in the past few thousand years goes against all received wisdom. Weren't we taught that natural selection operates over millions of years?

Yet recent evidence indicates that we have got this wrong. A gene that gives people the ability to digest milk after infancy, for example, was recently shown to have arisen and spread with the invention of dairy herding several thousand years ago.

The genetic evidence stems from samples taken from people alive today. By looking at how a gene's sequence varies among populations, we can work out how long ago it arose and chart its spread round the globe.
Arguably, information about the past can be obtained more directly from ancient human remains that have been preserved by accident or design. By comparing them with modern-day humans, we can work out just what civilisation has been doing to our bodies.

Perhaps the best-known difference is that westerners have got fatter, thanks to our calorie-rich diet and less active lifestyle. Obviously, that change would be reversed if we returned to hunting and gathering to find our food. A less well-known trend is that we have been becoming less muscular, almost certainly because we have been using our muscles less and less. Bones that no longer support large muscles can themselves become punier, so our shrinking musculature can be tracked in the fossil record. Our bones have become more spindly or "gracile", with the overall diameter shrinking as well as the dense outer cortex of the bone becoming thinner in cross-section.

Christopher Ruff of the Johns Hopkins University School of Medicine in Baltimore, Maryland, has travelled the world to X-ray about 100 fossil leg bones going back over 3 million years. He also studied bones from three populations from the near-present: Native Americans from the American Southwest who lived about 900 years ago, and east Africans and US whites from the early to mid-20th century.

Between 2 million and 5000 years ago, Ruff's team documented an average fall in bone strength of 15 per cent. At that point, however, the trend accelerated, as there was another 15 per cent reduction over a mere 4000 years (Journal of Musculoskeletal and Neuronal Interactions, vol 5, p 202).

Ruff thinks gracilisation kicked in when we began to use tools that reduced physical exertion, starting with hand axes, through to ploughs and eventually cars. Our increasingly sedentary lifestyle means our survival has come to depend less and less on our strength.

How much of this process is due to genetic changes, and how much would be reversed if we returned to a Stone Age lifestyle? It's impossible to say, admits Ruff. "We don't know what genes control bone mass and there's no way we can go and sample these fossils and figure that out."

What we do know is that the body has an impressive capacity to respond to exertion over a single lifetime. Take professional tennis players: by looking at X-rays, Ruff's team has worked out that the humerus in their playing arm is more than 40 per cent stronger than the corresponding bone in the opposite arm. For comparison, non-athletes have only a 5 to 10 per cent difference. "That would suggest that if you were in the Stone Age and you were forced to travel longer distances and lift heavier things, you would probably develop stronger bones," he says.

It's an important finding, because it suggests that we retain our ancient capacity for strength - if only we work our bodies hard enough - and stronger bones mean fewer fractures. Broken hips were less common in the past, and are vanishingly rare in archaeological specimens, even accounting for the fact that lives were shorter then.

Civilisation is changing not only our physical features but also the size of our families, which alters women's hormone levels. Female hunter-gatherers would typically have had six or seven children and spent much of their adult lives pregnant or breastfeeding, both of which cut oestrogen exposure. In the west we have smaller families and it is now rare to breastfeed for more than a few months. Obesity, lack of exercise, the contraceptive pill and hormone replacement therapy also raise oestrogen levels. "For many reasons modern women are exposed to enormous amounts of oestrogen," says Israel Hershkovitz of Tel Aviv University in Israel. That is thought to be the main reason women today have a 1 in 8 chance of developing breast cancer over their lifetime.

Breast tissue does not fossilise, but there is a way that hormone levels can be tracked through history. Prolonged oestrogen exposure is thought to cause thickening of the skull on the inside, just above the eyes.
Using medical school collections, Hershkovitz's group has measured nearly 1000 skulls of women who were alive 100 years ago. The team also ran CAT scans on 400 living women. In a paper soon to be published in the American Journal of Human Biology, Hershkovitz and colleagues report this thickening to be 50 per cent more common than it was a century ago. Among women in their 30s, the prevalence has nearly quadrupled from 11 to 40 per cent.
There are other physical changes that are more mysterious in origin. We seem to have acquired a new blood vessel in our arms, called the median artery. In fact, this blood vessel is present in the embryo but according to textbooks it normally dwindles and vanishes around the eighth week of pregnancy, to be replaced by the ulnar and radial arteries. An increasing number of adults now have this artery, up from 10 per cent at the beginning of the 20th century to 30 per cent at the end.

Over the same period, a section of the aorta lost a branch that is one of several supplying the thyroid gland. One of those who has helped to document these changes is Rühli's former teacher Maciej Henneberg, now an anatomist at the University of Adelaide in South Australia. They could be due to differences in the diet and lifestyle of pregnant mothers, he speculates, or perhaps a relaxing of the forces of natural selection, thanks to modern medicine and welfare systems.

Disease origins

It is these kinds of uncertainties that leave some practising doctors less than impressed with the buzz around evolutionary medicine. We cannot know if evolutionary explanations are true, since we rarely have a complete picture of the past, points out retired American family physician Harriet Hall, who blogs as The SkepDoc. "Conventional medicine has a long record of successes," she says. "Evolutionary medicine hasn't proven that it has any real value."

That's not to say that documenting trends over time isn't useful, even if it only corrects the textbooks. If the arteries of a 20-year-old differ from those of a 90-year-old, it could affect how they should be treated medically. At the very least, surgeons need to know in order to operate safely.

Even our fingerprints have been changing over time. Henneberg's team took prints from 115 bodies donated to the University of Cape Town in South Africa (Perspectives in Human Biology, vol 4, p 229). They divided them into two groups: those who were born before 1920 and those born later. There were significant differences in their patterns: simple arches, tented arches and whorls were more common in the later group, and ulnar loops less so.
Fingerprints may seem like a trivial sort of change but one of Rühli's next projects may shed light on the origin of a serious disease. In the world's malarial zones a number of mutations have arisen that persist in the gene pool despite causing serious diseases, because they protect their carriers from malaria. One of these affects an enzyme in red blood cells called glucose-6-phosphate dehydrogenase (G6PD), and those who carry two copies of the mutation have a serious form of anaemia.

By studying ancient miners, Rühli's team hopes to narrow the window in time when the G6PD mutation could have arisen. On two occasions - once in 500 BC and once in AD 500 - a salt mine collapsed in what is now Iran, burying those working there and preserving their flesh. That has given us two samples from the same place preserved in the same way, 1000 years apart. Rühli's team is trying to get usable DNA from the salt mummies.

Sometimes these looks into the past shed light on our future risk of disease. One such case involves spina bifida, the birth defect that causes paralysis of varying severity depending on how high up the spine is affected. It happens when the embryo's neural tube, which develops into the spine and brain, fails to close up properly, leaving gaps in one or more vertebrae.

The incidence of spina bifida has been falling over the past couple of decades in most western countries, thanks to campaigns persuading pregnant women to increase their folic acid intake. But this could be obscuring a longer-term trend in the opposite direction.

There is a much milder and commoner form, known as spina bifida occulta, where the only affected vertebrae are in the sacral region at the bottom of the back, which stretches down from S1 to S5. Most affected people have no outward sign and don't even know they have it, although there is some evidence linking the condition with back pain and some rarer health problems.

There is now an array of evidence that spina bifida occulta has become more common. Some comes from work on human remains found by Henneberg at Pompeii, the Roman city buried when mount Vesuvius erupted in AD 79, in a project led by his wife, Renata Henneberg. Pompeii has provided a wealth of information since excavations began in the 18th century. "You find families trapped together with the mother trying to protect the children," says Maciej Henneberg. "These were the last moments of real people, frozen in time."
The Hennebergs looked at the rate of spina bifida occulta among the Pompeians. About 10 per cent had an unclosed S1 vertebra, compared with an estimated 20 per cent of people today. Vertebrae lower down the spine are now even more likely to be open. The bottom-most one, S5, was open in about 90 per cent of Pompeians, compared with nearly 100 per cent in people alive today.

True spina bifida is so rare it is impossible to gauge its past prevalence with any accuracy. When we look at spina bifida occulta, however, the spine as a whole seems to be taking on a more open structure - although folic acid may be able to counter this trend. What's behind the change? Henneberg thinks one possible explanation is the long-term gracilisation of the skeleton. Changes to genes controlling the long bones in the legs and arms could have knock-on effects on the spine. "There's less bone everywhere in the body," he says.

A different explanation is, again, that selection pressures on humans are easing. "There's no question that it's relaxing," says Henneberg. One hundred years ago, one-third of children died before the age of 5. Now practically everyone who's born survives."

This kind of talk often comes with dire warnings about weakening the human race, and in the past has triggered the eugenics movement. But today's evolutionists seem sanguine about the future. Rühli believes less selection pressure is not necessarily bad for a species' survival. "The more a [population] is under environmental pressure, the more it narrows the variability," he says. With humans today: "We see a higher degree of variability within the body. An increase in variability may be good."
Even if that means a rise in conditions like spina bifida occulta? If food or minerals become scarce in future, it might be better to have spindly bones, says Henneberg. "Who knows what the future might hold for the human race."

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So it appears we're getting weaker and just inventing our way into doing ever less work. Some gracialisation was bound to happen when people stopped hunting, but now people don't even farm any more so it may become even greater.
I don't regard gracialisation as a particularly good thing (accept in women) because less strength leaves us at a disadvantage and our psychology when it comes to breeding is still very primitive - women don't want skinny men, men don't want anorexic women.

[Albion]

Now something about the effects of farming on human psychology, a theory about how we became domesticated in behaviour.

Did the dawn of agriculture lead to a form of human artificial selection resulting in more passive, less suspicious individuals? Isn’t this a bit like domesticating animals?

When I first read of the influential archaeologist Ian Hodder’s ideas about the ‘domestication of the mind’, I couldn’t help thinking “eh?”

What Prof. Hodder was trying to do was to explain an apparent paradox at the dawn of farming. This is that for the average Palaeolithic individual, the disadvantages of hard work and lowered nutrition resulting from farming seem to outweigh its advantages. So why would they ever have taken up farming at all?

Ian Hodder essentially argued that farming was only possible because humans had been ‘trained’ to accept it. This was not the training of a Machiavelli-figure but a kind of group training. Once people were on-side about the concept of “that is wild and dangerous” and “this is tame and homely” it was easy to make them take up farming. This seemed like so much mumbo jumbo to me.

So I forgot about Prof. Hodder and his ideas. I wanted a better reason than that for why people took up farming. I came up, for better or worse, with trade. Of course, this turns out to be as unproveable as domestication of the mind.

Yet something recently has caused me to go back to Ian Hodder’s idea and look at it again. I have a feeling that ‘domestication of the mind’ and trade are not incompatible.

Meet the ancestors

It’s difficult to know what the normal habits of a Palaeolithic forager were. The clues – paintings and carvings of animals, as well as rather odd shaped, generally faceless women – don’t help much.

Some of these foragers were clearly great artists. Whatever, I still don’t think that I would have enjoyed an encounter with most of them. Generally they were probably distrustful of strangers to the point of extreme violence and killing. I suspect that our first meeting might have been nasty, brutish and short, at least for me.

Of course, at the time there may have been evolutionary advantages to this suspicious and agressive behaviour. A new foraging group in your territory would be competitors for the animals and plants that you saw as your own. Killing or scaring them away would seem the best option.

Our modern tendency to cooperate with most strangers, both at work and on the street, would have been incomprehensible to our Palaeolithic ancestors. Books such as ‘The Company of Strangers’ have long made the case that what humans have become in the twenty first century is a long way from where we started.

Love thine enemy

Yet this cannot have been the whole story. Genetic health requires that Palaeolithic clan groups must have brought in women (or men) from other groups to produce healthy and viable offspring.

Also the style of art known as Gravettian managed to spread across a large area of Europe about 25,000 years ago. If there had been excessive hostility between groups then it would have been impossible to generate and spread this pan-European art style. In fact, it would have been impossible to spread any of the innovations made by humans during the Palaeolithic.

So I’d guess that, yes, humans were more suspicious than they are now. However, there must have been groups or individuals that were less suspicious and, conversely, groups or individuals that were more so.

Neolithic trade and gambling

As Matt Ridley would no doubt tell you, the growth in trade over the last ten or so millennia has been pretty much exponential. Yes, there have been downturns, but overall the pattern is one way.

Trade has always been a gamble, but it’s much less risky than it used to be. For example, shipping crates of bananas from Surinam to Holland, you can be fairly sure that nothing’s going to sink your ship and that the bananas won’t go rotten during the journey.

Compare this with the gamble for any Palaeolithic individual wishing to make contact with another group just to swap stones. Her thoughts would probably be “What are the odds that I’m going to get through this with my life?” I could imagine it would’ve made her a bit jumpy.

The growth of Earth’s population, like trade, has also grown exponentially. But the population that has enjoyed this growth probably didn’t include the suspicious, highly violent end of the Palaeolithic human spectrum.

For when people first started to trade with others there would be an understandable desire to lower the risk and trade with the less dangerous groups or individuals. The suspicious and aggressive groups would have been shunned as just too risky to trade with.

Additionally, the advent of farming meant that it was possible to have more than one clan group living in the same area. This meant that there was no evolutionary advantage in being that suspicious.

Domesticating animals and humans

It seems reasonable to compare the situation above with the domestication of animals.

Archaeologists have long wanted to understand the way in which animals were first domesticated. However, twentieth century Soviet experiments with wild silver foxes showed how it is possible to get rapid results with artificial selection.

Animals in these experiments were selected or rejected according to their aggression levels. Aggressive animals would be culled when young. The small percentage of passive animals would live to reproduce. After 30 or so generations the experiments had managed to produce tame silver foxes.

When people were first domesticatng animals there was an evolutionary advantage to having herds with genetic diversity, but that also didn’t fight each other. Therefore the same selection methods as for silver foxes were probably used.

For humans, it is possible that the first traders and farmers followed a similar, though not identical strategy. By avoiding contact with suspicious and agressive groups they would control their own breeding patterns. By expanding their populations through farming they could outcompete the rest. As time went on, the farming population, relatively passive and accommodating, would outgrow the non-farming population.

Discussion

There are many factors that haven’t been taken into account above. I have not discussed the physical factors driving continued evolution, such as the role of disease in densely packed populations. Also, I would never dream of arguing for an entirely passive and money grabbing population created by trade and farming. There’s plenty of evidence to contradict that.

But I think that ignoring the role of artificial selection on the thinking of early farming communities is to miss something important. I think it also opens up the possibility that early farming populations were ripe for exploitation by cunning and aggressive nomad or forager populations once the technological conditions were right.

Either way, I think that Ian Hodder was on to something. Humans have been domesticated. However, this is probably not by training, as Hodder suggested, but by the only method that’s been shown to work, artificial selection.

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[Albion]

The short version of human history might go something like this: First we were prey, then we were hunter-gatherers, then farmers — and from that came civilization.

Not quite, said James Scott, a celebrated Yale political scientist who delivered the first of the season’s Tanner Lectures on Human Values Wednesday (May 4) in Lowell Lecture Hall. In fact, he said, humankind — attached to foraging — embraced the growing of fixed crops only reluctantly, following millennia of halting and hesitation. After all, making the transition from nature to civilization required trading a complex system of diverse nutrition and robust health (foraging) for a more regimented style of living that shortened lives and replaced leisure with drudgery (farming). Borrowing a phrase from an earlier scholar, Scott called early hunter-gatherers “the original affluent society.” But embrace agriculture we did, eventually. It was a step that also made nation-states possible, which in Scott’s view triggered large-scale, authoritarian styles of governance that have — and still do — misguidedly control human enterprise from a central core of power. As a result, history is littered with the utopian failures of states that use central planning to manage activities like farming, said Scott — often with murderous results. (Think of China’s disastrous Great Leap Forward, for instance, or the Soviet Union’s clumsy collectivist farms.) Scott, invited to deliver the Tanner Lectures in their 33rd year, directs the Agrarian Studies Program at Yale and is a student of peasant politics, revolution, class relations, and anarchy. The prestigious Tanner Lectures are delivered by different scholars annually at nine universities in the United States and abroad, the legacy of the late Utah industrialist Obert Tanner. At Harvard, they are sponsored by the Office of the President and by the Mahindra Humanities Center. Scott has devoted decades of scholarship to investigating authoritarian governance and the coercive state projects that result, including those that are merely irritating (taxes and conscription) to those state projects that are tragic (slavery and warfare). Just the titles of his books speak volumes: “The Art of Not Being Governed” (2009), for instance, or “Seeing Like a State: How Certain Schemes to Improve the Human Condition Have Failed” (1997).

A counterpoint to these coercive states, Scott says in his scholarship, are the various “nonstate peoples” that resist dominance — outsiders of every kind, be they Berbers, bedouins or simply the homeless. Scott began his first of two Tanner Lectures with a confession: that his books so far have failed to completely explore the oldest state project of them all — “sedentarization,” the attempt by governments of every stripe, in every age, “to assemble rural people on fixed agricultural fields,” corralling them into political bodies that never seem to quite work. Being corralled this way is an unlikely fate for a species that spent the first 97 percent of its time on Earth as hunter-gatherers, said Scott, a lifestyle in which large-scale governance was impossible. The puzzle is “how we as a species ended up assembled in great clumps,” he said, “growing grain, tending livestock, and governed by the political units we call states and empires.” But the Tanner Lectures were an inspiration to unravel that puzzle, said Scott, though at “breakneck speed” and without the trappings of scholarship. Today’s (May 5) lecture will be more about those states and empires, he said, but the first — on May 4 — laid out the factors that led humankind reluctantly from free, roaming lives to lives of civilization, stasis, and encirclement around the domus — the ever more important home. That transition, over millennia, required three “world-shaping” forms of domestication, said Scott — of fire, plants, and animals. And once those three were tamed and contained, so was the fourth; humankind itself, he said, was the last of “Four Domestications,” the title of the first lecture. Domesticating fire came first and made all the others possible, said Scott. It transformed humans from the object of prey into an emerging dominant species with a source of warmth, light, safety, and cooked food. Cooking was a revolution that allowed Homo sapiens to reduce its gut, grow its brain, and expand its range of food sources. Around 500,000 years ago, fire also became humankind’s “greatest tool for reshaping the natural world,” said Scott — a means of transforming land into a diverse, renewed, and fertilized landscape of berry bushes and other sources of food. Fire-blackened fields were still a long way from the grain fields and the livestock pens of a much later era, he added, but they enabled humankind to “surround itself with its needs close at hand” for the first time. “Fire was our trump card as a species,” said Scott, and made once weak humans into “the world’s most successful invasive.” That domesticating plants was a strategy for species success is a harder argument to make, he said. For millennia, in fact, farming was overshadowed by foraging. But population pressures helped establish the idea of deliberate crops. In the end, farms became the locus of “fully domesticated plants,” favorite grains and fruits that were dependent on human attention, said Scott. Once humankind took “that fatal step” into farming full time, the routines required set the tempo of life itself, reshaped gender roles, and became “the very center of the civilizing process.” Farming also brought into a tighter sphere all of the natural things humans needed to live: fire, plants, and eventually domesticated animals, which became a sort of penned game as well as renewable sources of calories like milk, cheese, and eggs. In all, farms drew “denser and denser rings around the domus itself,” said Scott, and became a means to “relocate the natural environment” at the very door of a person’s house. The domestication of animals — in place at first about 8,000 years ago in the case of sheep, goats, and pigs — was in part made possible by grain farming. Farm animals also became “servant foragers” of a sort, said Scott, docile beings capable of eating all kinds of inedible plant matter and turning it into calories humans could use. The same animals could “mimic the effects of fire,” he said, by clearing land, after a fashion, and fertilizing fields. But the “Neolithic revolution” of farming came with consequences, said Scott. He outlined a grim narrative that contradicts the one we learn in school, in which the superiority of farming is “underwritten by a powerful mythology.” Part of that pro-agriculture myth was that “no one chose to remain nomadic,” said Scott, but in fact farming for millennia just supplemented foraging, and did not replace it. A permanent move to farming also brought increased mortality rates, smaller bodies, bone and teeth deformities, and iron deficiencies that hit women hardest. Cultivated plants were more reliable, but they were less nutritious too. Gone also were the complex sources of calories obtained by foraging, replaced by a diminished variety of grains. In addition, farms meant greater population density, closer contact with animals, and the attendant “heaps of pests and pathogens,” said Scott — a “perfect epidemiological storm” for humans already weakened by their increasing domestication. In all, he said, civilization’s embrace of farming meant a “slow-motion plunge” from health to disease. But there is a paradox too, said Scott; a rise in birthrates came with the rise of agriculture.

http://phys.org/news/2011-05-nature.html

That last sentence about agriculture is interesting - some argue aid in Africa artificially keeps their population high (by feeding them) which in turn leads to famine because they don't grow enough food.