Evolution takes place because we successfully adapt to changes in our environments over vast amounts of time, leading to the false belief that evolution occurs only when the environmental change is stable over time so that the adaptive changes can take hold and the species can flourish. After all, if the adaptative pressure goes in one direction and then reverses course, the adaptive changes might never happen or become maladaptive and cause extinction. But the climatic record during human evolution has been extremely variable, especially in the recent past, so it does not support the idea that environmental stability produced our adaptation. This post will discuss the accepted definition of ice ages, glaciations, interglacials, and their effect on human evolution. 

Ice Ages

An ice age is millions to tens of millions of years when temperatures are cold, and ice sheets like the north and south poles cover large areas of the earth. As you can see in the diagram above, the normal state of the earth is long periods of warm climate with shorter punctuations of cold weather when polar ice caps form. Again, the presence of polar ice caps is delineated as an ice age. The earth has no polar ice caps between the ice ages, and the sea level is much higher. By this definition, we are currently in an ice age and have been in one for millions of years. The periods between ice ages are many times longer than the ice ages that punctuate them.

There have been five ice ages over the last 2 billion years, and the most recent one began approximately 3 million years ago and continues today, so we are, shockingly, in an ice age right now. I understand the disbelief; after all, we have been told about the perils of global warming, so most people have mistakenly thought that it is warmer than normally seen on earth. But as I have stated, the earth is usually much warmer than it is now. The important takeaway is that it started warming about 14,000 years ago. We have the good fortune of being in an interglacial, so it is less cold than it could be. As much as the experts want colder weather, we could not readily support global agriculture in times of glaciation. As in Greenland, the Vikings settled there when it was warmer during the Medieval Warm Period but could not sustain themselves in the more recent cold. But humans live there; the Inuit survive in smaller numbers and don't rely on agricultural settlements.

Glaciation and Interglacials

Most people today mistakenly use the term ice age for glaciation. We had a glaciation melt about ten thousand years ago, and most people refer to it as the last ice age, but this notion is completely incorrect. Within an ice age, temperature fluctuations cause the ice sheets to grow and shrink. Glaciations are when the ice sheets grow; when they retreat, the periods are known as interglacials. The diagram above shows five glaciations and interglacials in the last half-million years.

The Genetic Bottleneck Theory

Some scientists have espoused the idea that in sudden environmental changes, small, isolated populations can find themselves in a unique situation to evolve mechanisms to better cope with the environment while the vast majority of other, less fortunate populations perish. The newly-adapted population then spreads, causing their new features to dominate. Such was the thinking around the gigantic eruption of Mount Toba 74 thousand years ago. It was believed that it resulted in a volcanic winter that caused a bottleneck in human evolution where most humans perished, but a small African population survived and interbred to become better survivors who, with their new genetically superior survival skills, subsequently populated the rest of the earth shortly after that. Recent research has concluded that bigger volcanic eruptions do not always cause more climate cooling. Supporting this concept, the eruption's environmental effects were negligible in Africa, and populations of humans elsewhere appear to be stable. 1 So, what else caused a sudden worldwide migration of humans?

The Pleistocene Epoch

The Pleistocene epoch is the time period from about 2.6 million to 11,700 years ago. It was characterized by lower temperatures with more fluctuation than usual, resulting in frequent glaciations and interglacials. The last glaciation ended about ten thousand years ago, and we are again in an interglacial. The current epoch is called the Holocene and is not climatically different from the Pleistocene; however, the Holocene is differentiated from the Pleistocene due to the domination of humans on the earth, which is why it is also called the Anthropocene, the Age of Man. 

The First Humans

The first human species, Homo Habilis, appeared during the Pleistocene 2.3 million years ago. 2 Their use of flaked stone tools marked them as the first humans. Homo Habilis tool use broadened their diet and that of subsequent hominins. Meat, in particular, is a food that was obtainable in equivalent ways, with similar nutritional value, in virtually any habitat that early humans encountered. The environments subsequent members of the human evolutionary lineage occupied varied greatly from grassland to forest to tundra and more. Using stone implements and our acute brains helped us exploit multiple differing environments, which helped our human ancestors to increase their ability to cope with changing habitats rather than specializing in a single environment, and, as I have stated, the variability in environmental conditions was greater in the later stages of human evolution than in the earlier stages. 3

How Human Populations Spread to Different Global Environments

The ability to tolerate different environments due to tool use helped the dispersal of early Homo beyond Africa into Asian environments. Other things happened. Around this time, 2 to 1.5 million years ago, our legs elongated, further helping our dispersal. After 1.9 million years ago, the genus Homo is found in various locations in Asia, including some areas relatively far north. From 1 million to 200,000 years ago, our brains underwent a rapid increase in size that correlates to much better behavioral adaptations to novel environments. Shortly after that, we began controlling fire and building shelters. Finally, when fully modern humans arrived, large resource exchange networks began. These adaptations helped us generalize our survival to numerous, sometimes novel, environments.

Dr. Rick Potts and the Variability Selection Theory

Since environmental instability is the norm for humans throughout our evolution, Dr. Potts formulated the variability selection theory in 1998, which upholds the concept that humans increased their ability to cope with changing habitats rather than specialize in a single environment. Potts examined the hominin fossil record and the records of environmental change during human evolution to test the variability selection hypothesis and compare it with habitat-specific hypotheses. Dr. Potts used the difference between modern humans and Neanderthals to highlight aspects of his theory. Neanderthals had different ways than us of dealing with environmental challenges. For instance, modern humans had much more specialized tools enabling us to eat many more animals. We are the only species to have eaten everything from whales to insects to other high-level predators like cave bears. Additionally, Neanderthals did not have wide networks of exchange which limited their survival compared to us. Lastly, we domesticated dogs to help us hunt; Neanderthals did not, one of the many reasons we may have out-competed them for prey, causing their extinction.

The Metaverse?

Our evolution has made us the most versatile animal on the planet. Our big brains, dexterous hands, and ingenuity allowed us to survive in a wider range of habitats than any other animal. However, a spokesman for the World Economic Forum, Yuval Harari, stated recently that we will live in the metaverse. The metaverse is a yet-to-be-defined virtual reality experience. Oddly, people buy real estate there! Whatever it may become, I can't imagine it as a viable habitat. We may be able to imagine we live there, but we won't be able to procure food there.

We Need Each Other No Matter Where We Go

 I don't disagree that a large part of our survival is based on technology. First, we used primitive stone tools. Eventually, more complex tools like spears and bows and arrows. Finally, industrialization has us living in a constant state of year-round comfort and satiation. The idea that the metaverse will be another habitat we can thrive is ridiculous. We should be mindful that being human is cooperating to survive and nurture relationships, which is the most crucial element of our health, happiness, and survival. Other things go into health and happiness, like sunshine, activity, etc. Even if we colonize another planet, we must do it together as we have always moved into new landscapes with our shared humanity. Using our ever-expanding technology will help, but not if we surrender the other things that make us human, like activity and interaction.

The movie Wall-e came out in 2008 and was probably not far off the mark. In the movie, robots take care of everything, leaving humans to live a life of ease. As a result, they are morbidly obese, float around in hoverchairs, and appear to be completely oblivious to their surroundings. They drink "Food In A Cup," and are very lazy. Most of them have never even turned their heads from the holographic displays in front of them, with a video chat screen surrounded by ads. As I mentioned in last week’s post, Francis Pottinger stated that “cats that are prevented from hunting, subjected to a life of ease, and fed prepared, cooked foods show tendencies toward maldevelopment." Humans will not flourish either by doing so.