To remove tannins from acorns they need to be ground up and soaked. Online instructions for making acorn flour on websites providing hunter-gatherer recipe suggestions involve grinding the acorns before soaking them for up to a week, changing the water daily. The acorns are best dried with the shell and skin taken off before being ground up. The tannin removal process can be sped up by boiling. The resulting flour is tasty as well as nutritious and was consumed by hunter-gatherer groups whenever oaks were abundant. Humans have been making flour from acorns and other nuts and seeds for over 30,000 years, although the earliest bread so far found dates back only 10,000 years.
Making flour not only removed tannins, it also protected our teeth. The human bite is not particularly strong, and trying to chew on hard food can damage teeth. In the absence of a dentist, tooth decay and loss can be a serious issue, reducing the amount and types of food that can be consumed. Grinding seeds, nuts and animal bones was consequently an important innovation, and once it was invented those groups that used it would have had a survival advantage over those that did not. The technology consequently spread, and as it did so, local populations that adopted it would leave more descendants.
Any population has a replacement rate, which is the average number of offspring each individual must produce for the population to remain the same size from one year to the next. If you and your partner have two children, and both survive until adulthood, you will have replaced yourselves. If those two children each find partners and themselves have two children that survive to adulthood, they too will have replaced themselves, and you and your partner will have four grown-up grandchildren. When this happens to everyone, a population will remain the same size into the future. Yet not all individuals survive from birth to adulthood, and this means that the replacement rate in human populations with good healthcare provision is a little over two children. In cases where mortality between birth and sexual maturity is higher, the replacement rate is also higher, and the hunter-gatherer replacement rate may have required each woman to produce between four and six children. However, they did better than this as hunter-gatherer populations spread to conquer the globe, and this means their reproductive rate was higher than the replacement rate.
A population that does not continually increase or decline in size has some process that keeps its size within bounds, and the process that does this is described as ‘limiting’. Populations of wild animals are often limited by predation, food availability, disease, suitable breeding sites, or even the ability to find a mate. Early in our history, Homo sapiens may have spent a 70,000-year period soon after they evolved from Homo erectus being restricted to a small patch of green, lush land in Botswana in an area that is now Lake Makgadikgadi. The population would have been stable for millennia and expanded only following climate change. Not all scientists accept this interpretation of the data, but it would not be surprising if our ancestors’ population was limited by predation, food availability or disease at some point in its past.
Technological advances freed our ancestors to reproduce at a rate faster than the replacement rate. An increase in the ability to acquire resources, and to reduce the rate of mortality from predators, meant that local populations would have increased. As the local population increased, the amount of food available on the landscape would have declined. As life became harder, individuals began to disperse, and it was this process that led to humans covering most of the globe. Each technological advance allowed our ancestors to acquire more food and to produce more young. But more mouths require more food, and this would have driven down available resources. Without the advent of newer technology, some people would have upped sticks and moved to pastures new.
Humans are heterotrophs, which means they get their energy from feeding on other lifeforms. The success of an individual heterotroph comes at a cost to something else. Grazers thrive by eating grass, browsers by eating trees and shrubs, and carnivores by eating other animals. Humans are no different, and it is why we are negatively impacting our planet’s natural environments. You might think that this is a recent innovation, but it is not. We have impacted nature since our earliest days, and we will continue to do so into the future.
Humans are bad at sharing their lands with other large animals unless they have domesticated them. Across the globe, people persecute wolves, lions and bears, and we are in the throes of driving rhinos and elephants extinct. Even large marine organisms, such as whales, seals, and large sharks that pose very little risk to us, are not spared. Sometimes we persecute them because we fear them, other times it is to eat them, to turn them into trinkets, or to satisfy the misguided belief that some attribute of an animal’s organ will manifest in you. Our modern-day dislike of large animals is not a new phenomenon. As humans colonized new parts of the globe, they routinely drove large species extinct. Some scholars shy away from blaming our ancestors for the carnage because changing climate also often correlates with the demise of some large animals and this means it can be argued to play a role. The issue with blaming the weather is, first, that climate change allowed humans to conquer new lands, and second, many of the disappearing species had survived earlier periods of climate change without dying out. We have never been good at living with large animals, and quite probably never will.
A second line of evidence for our negative impact on nature comes by looking at the distribution of animal body sizes on continents in the presence and absence of our ancestors. An examination of the body sizes of animals on each continent 125,000 years ago suggests that early Homo sapiens rid landscapes of large animals from very early in our history.
The distribution of body sizes found on a land mass is related to its area, such that larger bits of land tend to have higher average body weights of animals. Africa is one of the world’s largest continents so we would have expected it to have many large animals, but 125,000 years ago, by the time Homo sapiens had evolved, that was no longer the case. It contained fewer large animals than predicted by its size. The big beasts were already largely gone. As humans moved across the world, they continued the killing. Species such as the elephant bird of Madagascar, the giant ground sloth of South America, the marsupial lion of Australia, the giant cave bears of Northern Eurasia, and woolly mammoths were all driven extinct. Their demise was our ancestors’ success, but eventually there was nowhere new to disperse to, and new technology was required for our populations to grow.
As local hunter-gatherer populations increased in size, neighbouring groups would encounter one another more frequently, opening the opportunity for trade, and war. In some parts of the world, different hunter-gatherer groups from different environments began to seasonally meet up to trade goods and perhaps find partners. Structures began to appear, such as Earth mounds and early buildings, in places like Lepenski Vir in Serbia, which hunter-gatherers used as a seasonal meeting place. The next step was towards living year-round in one place, and the development of living in the same house year-round came hot on the heels of another key innovative technology: agriculture.
The oldest evidence of agriculture comes from the shores of Lake Galilee, 23,000 years ago, where edible grasses were cultivated on a small scale by the Ohalo II people. Despite the obvious ability to farm crops, widespread adoption of agriculture in the region took a further 11,500 years, by which time pulses such as lentils, peas and chickpeas, and grasses including wheat, rye and barley, were cultivated. Climate change may have contributed to the declines in animal abundances, along with hunting, and such change could likely have also altered the distribution of nut and fruit trees in the region, leading to agriculture becoming a necessity.