For a long time archaeologists, biologists and historians believed that the origins of agriculture more than 10,000 years ago marked the end of human evolution.
The beginnings of civilization – and eventually of industrialization – were seen as simply reinforcing this notion.
Humans had altered the environment to such a great extent that the forces acting on hunter-gatherers through natural selection were simply no longer important. Culture came to dominate entirely, biology being now largely irrelevant to the chronicling of the human story.
That by shaping our environment – today even on a planetary scale – we had taken hold of our own biological destiny as a species.
It turns out that this view is largely wrong. Farming and subsequent developments in human history have dramatically altered, sometimes intensified, our evolution, rather than halting it.
Human evolution didn’t finish at the end of the Stone Age, it continues even today, but in many ways the drivers of natural selection have changed and have been influenced greatly by culture.
This is in part – a major part – why the quest to find some kind of palaeolithic ideal lifestyle or diet is ultimately futile; just a fad not founded in science.
Farming marked a major shift in our evolutionary history resulting in physiological changes associated with our ability to digest certain kinds of foods, dramatically altered our immune system, and changed our relationships with plants and animal in profound ways.
It may even have changed the colour of our hair and skin, according to new research by Iñigo Olalde and co-workers in Nature and by Sandra Wilde and her team in the Proceedings of the National Academy of Sciences USA (PNAS).
End of paradise
Archaeologists believe that agriculture began around 11,000 or 12,000 years ago in two regions, and independently: West Asia (Middle East) with the domestication of wheat, and animals like goats, and in China, with the domestication of millet, rice and pigs.
Dogs may have been domesticated at the same time. While various claims have been made about dogs being bred by hunters and gatherers, perhaps tens of thousands of years ahead of farming, they remain controversial.
Agriculture was also invented at a later time in the highlands of New Guinea and in the Americas, probably also independently of events in West and East Asia.
The beginnings of farming – what archaeologists call the Neolithic (“New Stone Age”) – were at a time when the world’s climate began to change at the end of the last Ice Age.
Warming occurred quite quickly following a relatively short cooling event known as the Younger Dryas (or “Big Freeze”), which lasted from around 12,800 to 11,500 years ago.
The period of warming that followed the Younger Drays marked the beginning of what geologists call the Holocene (or recent) epoch, the geological time we live in today, and it seems to have been one of the major catalysts for farming.
In fact, even where farming was introduced to other places (e.g. Southeast Asia and Europe) at later times (4,000 or 5,000 years ago), there seems to have been, at least in some instances, a clear association with changes in the climate.
Climate change on its own is not enough to explain such a major shift in human ecology and economy though. People had been hunting and gathering for close to 200,000 years, and some people still do today.
So, there was no inevitability to its development, nor was it part of an unbreakable historical and social continuum, despite what some 19th and 20th Century scholars had thought.
Archaeological evidence suggests that certain human populations had become more sedentary at this time, probably due to climate related environmental change, and so both thought about and used their environment in a different way to their ancestors.
We know, for example, that pottery was being made in China from about 20,000 years ago, probably for cooking, but maybe also for storing food during lean times. It’s use become more common during the Holocene, especially with farmers.
And people were also using the wild precursors and relatives of various plants like wheat, millet and rice, and rather than just gathering them, began experimenting with them, including cultivating and then breeding them, before farming eventually emerged.
Many hunter-gatherers today and in the recent past cultivated economically important plants without farming or domesticating them, and some farmers even returned to hunting and gathering.
Farming’s real impacts
Farming has been a profound changer of the planet. Everywhere that it was introduced, farmers cleared the land to make way for agriculture: wet or dryland forms.
There are long sediment cores from lakes in many areas like China, for example, that show powerfully the devastating effects early farmers had on the landscape.
The effects of farming were also profound for the people who adopted it, in both positive and negative ways.
It led to a population explosion – sowing the seeds (excuse the pun) – for the vast numbers of people alive on Earth today. Estimates suggest a worldwide population of just a few million people 10,000 years ago grew to today’s 7 billion, and within only a few hundred generations.
While the precise reasons why the population exploded are not yet clear, it seems that the food security enjoyed by these early famers – many hunter-gatherers are plagued by seasonal shortage and starvation – and apparent improvements to childhood survival from improved food availability were enough to cause a population boom.
At the same time, though, early farmers were exposed to a stack of new infectious diseases acquired from the animals they were now domesticating and handling through animal husbandry.
The vast majority of diseases suffered by people today around the world are zoonoses – acquired from animal sources or vectors – and most of them became an issue for humans with the domestication of animals and the clearing of land for farming.
The flu, common cold, measles, leprosy, cholera, smallpox, TB, schistosomiasis and many other infectious diseases prevalent today or recent past result from contact with animals in the form of animal husbandry, exposure to animal and human excrement, and contact with pest species like rodents that occurred more frequently with farming and a much more sedentary, and ultimately, urbanised lifestyle.
It’s likely even that malaria only became a major problem for humans with land clearing and changes to waterways by early farmers, but the scientific jury is still out on this one.
So, farming shaped our immune system, following the onslaught of these many new diseases, and even changed our red blood cells conferring resistance to malaria in some individuals.
In the face of major shifts in diet and behavior, natural selection also resulted in many genetic mutations arising; or in some instances already present mutations increasing greatly in frequency within human groups.
Such genes included those associated with lactose tolerance in adults, the metabolism of alcohol, detoxification of plant food compounds and the metabolism of protein and carbohydrates. There must be many more that are yet to be discovered, and some that may even underpin the many intolerances and allergies suffered by people today.
At the same time, major demographic shifts saw changes in the genetic variability and the composition of population gene pools.
Recent large-scale studies have found that more than 70% of protein coding gene variants and almost 90% of variants found to be deleterious in living people – whose ancestors were agriculturalists – arose in the last 5,000-10,000 years.
The rise to such large numbers in these disease causing gene variants is the result of the population explosion associated with early agriculture and gives a very real sense of how our diseases and lifestyle have been dramatically shaped by this practice.
Farming also changed our anatomy and physiology in sometimes quite surprising ways.
Sandra Wilde and her team sequenced the DNA of human remains from early farming and Bronze Age skeletons from Eastern Europe. Their study showed that changes to pigment producing genes occurred after farming arrived in the region around 5,000 years ago.
They suggested that the combination of light hair, eye and skin colour seen in Europeans may have resulted from a diet poor in vitamin-D and the need to produce more of it through increased UV light exposure and absorption.
Yet, anthropologists had thought that depigmentation was probably around much earlier, in hunter-gatherers, owing to limited UV exposure in Northern Europe. It may even have characterised the Neanderthals.
So, this new view is a major challenge to prevailing wisdom and suggests that pale eyes, hair and skin may be a very recent adaptation, or at least, only arose to high frequency very late in our evolution.
The other study, by Olalde and co-workers, actually fits with this idea rather well and quite independently. They sequenced the genome of an approximately 8,000-year old male skeleton from Northern Spain and found that his genes indicated he probably had pigmented skin but with blue eyes; a combination not found today in people of European ancestry.
The work shows that the spread of light skin pigmentation genes through natural selection was not complete in some European populations by the end of hunting and gathering. Moreover, it suggests that the genes responsible for light/blue eye colour may have evolved well ahead of changes in skin pigmentation.
This would suggest that these late hunter-gatherers were actually physically rather different to people in Europe today and that depigmentation occurred rather late, perhaps several times, and in association with farming.
There are many other fascinating aspects of this crucial event in recent human evolution, but I’m afraid, they’ll have to wait for a future post!
Originally published in March 2014.
Posted in: Incredible human journey