There is no way out of the imagined order,’ writes Yuval Noah Harari in his book Sapiens. ‘When we break down our prison walls and run towards freedom,’ he goes on, ‘we are in fact running into the more spacious exercise yard of a bigger prison. Ore writes that when Homo sapiens colonized Africa 70,000 years ago, we were just another animal living in a distant part of Africa. Now that Sapiens have evolved to the point where they virtually act like gods, they are responsible for producing new life forms, searching for immortality, and dominating the planet. Sapiens, according to Harari, have done considerably more harm than good thus far. Although humans have constructed empires, he questions whether or not this has improved humanity’s lot. From human life 70,000 years ago to the current day, human cultures have not improved over time, as many experts believe, and humanity is prospering today because we are so numerous and advanced as a species. As our societies have become more complicated, he believes people have become continually unhappier. The more powerful we grow, the more unpleasant life becomes for other creatures.
He is not alone in reaching this conclusion. Most people who write history on a grand scale seem to have decided that, as a species, we are well and truly stuck, and there is really no escape from the institutional cages we’ve made for ourselves. Once again echoing Rousseau, Harari seems to have captured the prevailing mood.1
When Homo sapiens colonized Africa 70,000 years ago, we were just another animal living in a distant part of Africa. Now that Sapiens have evolved to the point where they virtually act like gods, they are responsible for producing new life forms, searching for immortality, and dominating the planet. Sapiens, according to Harari, have done considerably more harm than good thus far. Although humans have constructed empires, he questions whether or not this has improved humanity’s lot. From human life 70,000 years ago to the current day, human cultures have not improved over time, as many experts believe, and humankind is prospering today because we are so numerous and advanced as a species. As our societies have become more complicated, he believes people have become continually unhappier. The more powerful we grow, the more unpleasant life becomes for other creatures.
Little discussed is that during the Cretaceous Period, a comet six miles wide, taller than Mount Everest and traveling at a hundred times the speed of a jet plane, targeted the earth.2
The dominant land animals on earth before the comet’s arrival were dinosaurs.3 Right up until that day, the future of the dinosaurs looked pretty bright. They were at the top of the food chain, without equal, and there were no signs of that changing.
We accomplished the extinction of other animal species through a combination of hunting and turning half of the earth’s dry surface into farms.3 Of course, domesticated animals, are a different story. Today, just a handful of species – cattle, pigs, sheep, goats, and Homo sapiens – make up 97 percent of the land animal biomass on earth. Homo sapiens continues to exterminate other species, except for those destined for our table. The current extinction rate for all species is now more than 100 times higher than before. The global population of vertebrates has declined by 52 percent from 1970 to 2010.4One-quarter of all mammals and 10 percent of all plant species today are threatened with extinction.4 All these species, including the other humans, have vanished into the mists of history. The 99 percent of all species that once lived and are now dead are not around to contemplate the prospects for their survival. At one time, the future must have seemed bright for many of these now-extinct species. If given to contemplating their fate, the dinosaurs were probably looking forward to dominating the planet for many millions of years to come. Like us, they might have expected to survive because they had always done so in the past. But if a poll were taken of all species, the survivors and non-survivors, on the question of whether the earth is a hospitable place for life, about 99 percent would vote no. The only ones likely to vote yes – the 1 percent – are those that happened to survive.
We are fortunate that a small comet passed by us in 1736. We are equally lucky that a large one struck the earth 6 million years ago.
During the Cretaceous Period, a comet six miles wide, taller than Mount Everest and traveling at a hundred times the speed of a jet plane, targeted the earth.5 The comet (or asteroid; exactly which is still debated) entered the atmosphere, created a vacuum that sucked up hundreds of millions of tons of dirt into the clouds, and then smashed into the Yucatan Peninsula with the energy equivalent of a billion atom bombs, leaving a hole in the ground twenty-five miles deep and more than one hundred miles wide. The resulting fires circled most of the planet, burning forests and plant life, instantly roasting any animal in its path into charred ash. Within minutes, the “ejecta” – liquefied rocks sent into the atmosphere from what is now Mexico – rained down upon the planet, and a hail of lethal projectiles shredded animals not previously incinerated into little pieces of bone and flesh. The shock to the earth’s crust set off magnitude 12 earthquakes around the globe that shallowed up parts of whole continents, ignited massive volcanic eruptions that covered millions of square miles of land in molten lava, and triggered tsunamis that flushed sea life hundreds of miles inland. Ninety percent of the biomass of the earth was suddenly gone.6
And then it got cold
The ejecta and dirt in the clouds smoke from planetary-scale forest fires, and ash from volcanic eruptions blocked the sun’s rays. Global temperatures may have plummeted as much as fifty degrees over land and thirty-six degrees over the oceans. Less than 1 percent of sunlight reached the planet’s surface, halting photosynthesis. Many creatures still alive soon starved to death on frozen landscapes.7 The earth had gone from fireball to snowball.
Bad News for Dinosaurs: Good News for Us
The dominant land animals on earth before the comet’s arrival were dinosaurs.8 Right up until that day, the future of the dinosaurs looked pretty bright. They were at the top of the food chain, without equal, and there were no signs of that changing. Nothing indicated that the planet was anything other than a habitat particularly well suited to a dinosaur’s way of life.
If Homo sapiens had been alive when the comet struck, we would not have made it.9 But some animals did survive. A few tiny dinosaurs with wings were not killed. Maybe they were nesting in caves on that fateful day, or flight allowed them to scour the earth for food, such as seeds or the roasted animal carcasses that littered the earth. In any case, these small, winged dinosaurs managed to find food and evolved to become today’s birds. Many species of fish, protected by the vast, deep oceans, also survived. And a few small mammals, about the size of rodents, somehow lived through this global holocaust. The descendants of these rat-like creatures would evolve to write books about dinosaurs and survivor bias.10
The king of the dinosaurs was Tyrannosaurus rex or T. rex for short. Some forty feet long, weighing seven or eight tons, T. rex was one of the largest meat-eating animals ever to walk the face of the earth.11 Its skull was five feet in length with eyes the size of grapefruits and a jawbone lined with fifty or so knife-sharp teeth.12 Unlike us, T. rex could regrow broken teeth, which was helpful given its table manners.13 The king of the dinosaurs benefited from exceptional senses: binocular vision thirteen times better than modern humans, and the ability to hear and smell other animals at great distances.14 Above all, T. rex was thought to have been among the smartest animals around at that time.15
When a large comet struck the earth, this was bad news for dinosaurs but good news for us. Most believe that Homo sapiens could not have coexisted with such carnivorous beasts. We probably would have been a tasty appetizer: a tall, moderately sized, fleshy mammal who ran upright (easily spotted) and could not run that fast (easily caught). We can be thankful our ancestors were small, ground-hugging, sub-snack-sized rodents, not worth pursuing. Probably our ancestors’ main concern was not to get accidentally stepped on. We have not discovered any preserved T. rex or other dinosaur brains, so the best evidence of intelligence is the encephalization quotient (EQ), the ratio of brain mass to body size. As an indication of intelligence, EQ has drawbacks because the size of the individual components of the brain is important. For example, the size of the neocortex matters more than that of the limbic system as an indicator of intelligence. Nevertheless, EQ is roughly correlated with IQ. T. rex had an EQ of 2.0 to 2.4.. That is about twice that of a dog, more than a chimpanzee, and about one-third of a modern adult human.16
If T. rex had survived, we can only speculate how far another 65 million years of brain evolution would have taken their species. When humans first evolved, our intelligence was about the same as that of T. rex. During six million years of human evolution, our brain size has almost tripled: Our EQ started at 2.5 and eventually rose to 5.8.1719 But T. rex would have had a 65-million-year head start on brain evolution. Even if Homo sapiens somehow could have found a way to coexist with T. rex, it is unclear which would have become the more intelligent and dominant species.
A Planet Better at Preserving Fossils than Life
Sixty-five million years ago was not the first time most living organisms on earth were exterminated. In fact, the space rock that killed the large dinosaurs was the most recent of five mass extinctions, defined as events in which most species on earth perished.
The “big five” mass extinctions and the percentage of species lost were:
• Ordovician: 444 million years ago (mya), 86 percent
• Devonian: 375 mya, 75 percent
• Permian: 251 mya, 96 percent
• Triassic: 200 mya, 80 percent
• Cretaceous: 65 mya, 75 percent
If we had been around during any of those five mass extinction events, we could not have survived. We are fortunate not to have been alive during the first 95 percent of the earth’s 4.5-billion-year history.
In particular, the Permian mass extinction, known as the Great Dying, was a close call for all life on earth. A dramatic global rise in temperatures due to volcanic eruptions dumping massive amounts of CO2 into the skies baked to death almost every land species. Oceans turned acidic, burning through the gills and shells of most sea life. If all life had ended, we don’t know how long it would have taken for it to restart, if ever. Even if it had, we don’t know how much time would have passed before life once again reached the Permian stage of evolution. The evolutionary climb to the heights of Permian life took over four billion years after the earth formed. Hence, life might not have restarted, or evolution could have followed a different path. It is doubtful that any other path would have taken the same millions of twists and turns that yielded. Homo sapiens. We are lucky descendants of the fortunate small percentage of all species that have survived these mass extinctions.
Homo sapiens has existed as a distinct species for more than 200,000 years. Despite that, modern-day humans, as demonstrated by DNA evidence, evolved from a group of common ancestors who lived just seventy thousand years ago.17 After numbering perhaps hundreds of thousands of individuals at one time, the number of Homo sapiens fell to as low as several thousand individuals during this period.18 Such a substantial fall in numbers risked the extinction of our species: A population of merely thousands provides insufficient genetic variation for natural selection to adapt to environmental change and can lead to life-threatening genetic deformities from inbreeding.
The causes of this “bottleneck” in the Homo sapiens population are still debated. The most likely explanation is that during this time, a volcano, whose caldera today is Lake Toba in Sumatra, Indonesia, erupted in the largest explosion on earth in the past two million years.19 The Toba eruption spit ash into the skies that blocked out the sun’s rays, cooling the planet for more than a thousand years. However, some have argued the impact on the climate of equatorial Africa, where most Homo sapiens lived, was not significant.20 Other reasons for the population bottleneck could be that Homo sapiens were outnumbered by other humans, such as the Neanderthals, and may have suffered devastating attacks from these competing human species. Diseases could have also played a role, but determining the presence of pathogens from ancient skeletal remains is challenging. Or maybe it was some combination of all the above. Regardless, Homo sapiens barely survived, passing through a tight population bottleneck that could have easily led to our extinction.
As survivors, we tend to believe that the survival of our species was likely, even inevitable. This is natural. We survived the journey, so we are inclined to conclude that the journey must not have been perilous. But that fails to account for survivor bias. The path we took might have been one of the few that did not literally dead-end.
What we do know is that most species don’t make it. Ninety-nine percent of all species that once lived on the earth is gone.21 The vast majority of species on our planet have lasted from one to ten million years.22 Mammals like us are particularly vulnerable, surviving only about a million years on average.23 Compared with many other species, humans have a larger mass, which requires more energy when we hunt for food – and offers more food when hunted. Our warmblood demands reliable nutrients to maintain a constant internal body temperature. Our reproductive cycle has a high infant mortality rate (and maternal mortality rate), and we birth helpless infants completely dependent on adults for survival. These vulnerabilities are exacerbated by extended adolescence and, therefore a greater risk of death from predators. In addition, lower birth rates constrain our ability to adapt to a changing world through natural selection. Homo sapiens can procreate about once a year, but cockroaches give birth monthly. Some bacteria divide into new cells every twenty minutes.
The primary reason species don’t last is because the earth’s physical environment constantly changes. For all but a few species, the speed of that change eventually outruns the pace of adaptation. Charles Darwin called this series of adaptations “evolution,” which he defined as “descent with modification.” But the earth’s physical environment changes faster than just about any organism can adapt.24 Sometimes the change in the environment is gradual, such as an ice age, and other times sudden and violent, like a comet strike, a massive earthquake, or a volcanic eruption.
In any case, the earth is better at preserving fossils than life. Despite all this, Homo sapiens has survived and flourished. We dominate the landmasses of the earth from soaring mountains freezing in the clouds to tropical islands baking in the sun. We are the most intelligent species that has ever lived, as complex, symbolic language gives us the amazing ability to share knowledge with billions of fellow humans and pass on what we have learned to subsequent generations. In the next hundred years, we may even extend that domination to the planets whirling around our sun.
But our journey to today’s world was actually quite perilous. Some fifty thousand years ago at least five human species – Homo Denisova, Homo Floresiensis, Homo Naledi, Homo Neanderthalensis, and Homo Sapiens – coexisted on earth.25 Our species is the only survivor, the last humans.
Two Enter, One Leaves
Homo sapiens first appeared in northern Africa around 200,000 BC, the descendants of an early human species, Homo erectus. Sometime around 120,000 BC, Homo sapiens started trickling up into Europe, and then a large wave migrated north about 50,000 BC. There, we encountered Homo neanderthalensis, more commonly known as the Neanderthals.
Neanderthals were the most dominant human species at that time, outnumbering all others combined.26 Neanderthals had left Africa much earlier, about 800,000 BC, and moved up into Europe. By 400,000 BC, Neanderthals were spread throughout Europe and Asia.
Named after the first specimen found in 1856 by miners in the Neander Valley of Germany, Neanderthals shared many anatomical and cultural characteristics of Homo sapiens. Neanderthals were comparable in height, although much heavier in the body, with stronger and thicker arms and legs, a protruding jaw, and a thick-walled skull that rode on top of broad shoulders. Homo sapiens and Neanderthals were equally advanced. Neanderthal brains were as large as those of Homo sapiens,27 and like Homo sapiens, Neanderthals had language skills.3035 Both species shaped stone tools, crafted jewelry, painted cave walls, buried their dead, and lived on comparable diets.3136 Although physically imposing, Neanderthals in other respects were not that different from modern Homo sapiens. It has been said that a Neanderthal on a New York City subway would go unnoticed “provided that he was bathed, shaved, and dressed in modern clothing.”28
Within thousands of years of Homo sapiens arriving in Europe, Neanderthals died out, followed by the extinction of the other human species around the globe.29 The cause of such a rapid extinction of all humans on earth except for Homo sapiens is unknown. However, archaeologists have put forward several explanations. The most commonly accepted theory is that we slaughtered them, or what has become quaintly known as the Replacement Theory.30
As Homo sapiens moved into the Neanderthal territory, the frequency of violent interactions likely increased. There are indications that Homo sapiens had better language abilities than other human species, although our language skills at that time would still have been primitive and limited.31Consistent with an ability to better coordinate and communicate, Homo sapiens might have been more cunning warriors. It appears many Neanderthal men met an unnatural demise. This theory is supported by Neanderthal male skeletal remains that evidence skulls pierced by arrowheads or foreheads caved in by rocks. One survey of male Neanderthal skeletons showed that 40 percent suffered traumatic head injuries.32 There is also evidence of widespread cannibalism. Neanderthal skulls were often broken in places that would facilitate the extraction of juicy brain matter, and long bones were shattered in ways to ease the scooping of moist bone marrow.35
Homo sapiens also bred with Neanderthals. DNA evidence confirms that Homo sapiens carry genomes from Neanderthals that range from 1.5 percent in Europeans to 2.1 percent in Asians.36 Homo sapiens men may have killed Neanderthal men to access Neanderthal women.37 Given the small bands of hunter-gatherers in which humans traveled at that time, interbreeding within a group of forty or fifty individuals could produce genetic anomalies. Homo sapiens men who reproduced with Neanderthal women gave their offspring an evolutionary advantage.
An alternative explanation is that Homo sapiens were better hunters, and eventually the Neanderthals starved to death. It is not clear why that would be the case: Neanderthals were physically stronger and had established themselves in Europe and Asia long before us. Another theory is we drove Neanderthals to extinction because we domesticated wolves (today’s dogs) for hunting and the Neanderthals didn’t.3840 It is difficult to know just how important dogs were to food gathering or keeping watch for predators. Still, it seems unlikely that pets – even working pets – are mainly responsible for the extinction of the Neanderthals. Yet another theory is that Homo sapiens infected Neanderthals with lethal diseases we carried within us from Africa. Because the Neanderthals left Africa hundreds of thousands of years before us, they may have lost immunity to African pathogens.3941 This would be consistent with other mass human genocides, such as when Europeans arrived in the New World. However, particular diseases are difficult to detect in fossils, so there is no direct evidence of the “disease out of Africa” theory.
Based on what is known recently, the extinction of the Neanderthals was most likely due to Homo sapiens slaughtering Neanderthal men and capturing Neanderthal women. With the Neanderthals out of the way, we could have readily vanquished the remaining less-numerous human species employing a similar strategy. However, the Neanderthals could have just as easily won this interspecies battle for survival. In fact, given their vastly greater numbers and far superior physical strength, Neanderthals probably were the odds-on favorite. And then Neanderthals would have been the ones writing books about those primitive, now-extinct Homo sapiens.
Furthermore, we did not just kill off other humans. After vanquishing our nearest genetic kin, we proceeded to exterminate many of our animal predators. We hunted to extinction those whose meat we fancied.40
Originally, when Homo sapiens spread throughout the globe, large animals, known as megafauna, roamed every continent. There is not enough space in this book to list the animals we hunted to extinction, but some examples are straight-tusked elephants, woolly mammoths, woolly rhinoceroses, giant deer, cave bears, and cave lions in Eurasia; marsupial lions, giant kangaroos, a giant python, two species of crocodiles, and all large flightless birds in Australia; mammoths, giant elephants, giant sloths, giant armadillos, stag moose, mastodons, and the American lion, which was larger than its African cousin in the New World. Before Homo sapiens arrived, camels and zebras roamed the plains of North America. Horses thrived for hundreds of thousands of years before we drove them to extinction on the North American continent around 12,000 BC. (Today’s horses were later reintroduced into the Americas by Spanish settlers in the fifteenth century.)
By 10,000 BC, Homo sapiens had killed off 80 percent of big animal species in the Americas, basically those large enough to be worth the meat.42 Some animals we didn’t hunt to extinction but dramatically reduced their number, and then we put them in-game parks or zoos. Lions have declined from 450,000 to fewer than twenty thousand today, and there were once over one million chimpanzees in Africa compared with an estimated 200,000 currently.44 The total mass of wild animals is now one-sixth of pre-human levels.43
We accomplished the extinction of other animal species through a combination of hunting and turning half of the earth’s dry surface into farms. Of course, domesticated animals are a different story. Today, just a handful of species – cattle, pigs, sheep, goats, and Homo sapiens – make up 97 percent of the land animal biomass on earth.44Homo sapiens continues to exterminate other species, except for those destined for our table. The current extinction rate for all species is now more than 100 times higher than before.45 The global population of vertebrates has declined by 52 percent from 1970 to 2010. One-quarter of all mammals and 10 percent of all plant species today are threatened with extinction.46 All these species, including the other humans, have vanished into the mists of history. The 99 percent of all species that once lived and are now dead are not around to contemplate the prospects for their survival. At one time the future must have seemed bright for many of these now-extinct species. If given to contemplating their fate, the dinosaurs were probably looking forward to dominating the planet for many millions of years to come. Like us, they might have expected to survive because they had always done so in the past. But if a poll were taken of all species, the survivors and non-survivors, on the question of whether the earth is a hospitable place for life, about 99 percent would vote no. The only ones likely to vote yes – the 1 percent – are those that happened to survive.
Our future survival may not be as favorable as they seem
Our journey as a species to reach the present day has been fraught with many dangers. We have come close to extinction numerous times, like most species borne on this planet. If Homo sapiens had evolved before the last 65 million years of the earth’s 4.5-billion-year history, we would not have survived any of the mass extinctions. Since then, threats to our survival have come in the form of periodic ice ages and global warmings, as our planet has tried to freeze or boil us to death alternately. About seventy thousand years ago we barely squeezed through a population bottleneck. Some fifty thousand years ago we battled with the dominant human species on the planet and somehow lived to tell the tale.
Therefore, we should be cautious about becoming overly optimistic about our future. If the past is prologue, then the odds of future survival may not be as favorable as they seem. The journey ahead may present just as many, or even more, opportunities to take a wrong turn, leading to joining the other 99 percent of species that are now extinct.
But that is not the perspective most of us have about our evolutionary history. We somehow survived all these threats to our survival in the past and therefore believe we will somehow continue to do so in the future.47 But this is just an example of survivor bias. Our perspective on our evolutionary history is distorted because we are one of the few species that made it. The species that didn’t would have a different view. We can be easily fooled when we are one of the few winners. Even though our evolutionary journey to the present day was perilous, many argue that the road ahead presents significantly fewer dangers. After all, Homo sapiens currently rule the planet. We have wiped out or put in zoos any species that threatened us. We have developed powerful technologies to bend the physical world to our will and enjoy a standard of living hundreds of times greater than our hunter-gatherer ancestors. To mention two nuclear war and global warming, the risks of extinction for Homo sapiens are greater than ever.
About seventy-five years ago, we placed in the hands of a few the ability to exterminate billions with atom bombs. Around the same time, we started to spew large amounts of CO2 into the atmosphere, which could someday trigger a runaway greenhouse effect that fries all life on earth to a crisp. I will argue these new existential threats put us at greater risk of extinction than at any time since we battled for survival with the Neanderthals fifty thousand years ago.
Remarkably, the above two mentioned dangers were predicted sixty-five years ago by a Hungarian immigrant to the United States. The man who saw this clearly during the 1950s, both the upsides and downsides of technology, worked at the Institute for Advanced Studies at Princeton and was a friend of Abraham Wald. This professor cautioned that new technologies have unforeseen consequences. In 1955, as he lay dying of cancer near the end of his life, this professor wrote an essay in Fortune that laid out his concerns. He foresaw much of what would happen in the years to come, including the proliferation of nuclear weapons and global warming. His essay was entitled “Can We Survive Technology?”
1. David Graeber and David WengrowThe Dawn of Everything: A New History of Humanity.2021, p. 504.
2. Brusatte, Steve. (2018). The Rise and Fall of the Dinosaurs. HarperCollins. New York, p. 204.
3. Brannen, Peter. (2017). The Ends of the World. HarperCollins. New York.. p. 238.
4. Walsh, Bryan. (2019). End Times. Hachette Books. New York, p. 149.
5. Christian, David. (2011). Maps of Time. University of California Press. Berkeley, California, p. 142.
6. Descriptions of the effects of the comet or asteroid are a combination of Brusatte (2018), p. 314–315 and Brannen.
7. Walsh, Bryan (2019), p. 17.
8.The descriptions of dinosaurs come from Brusatte (2018).
9. Brusatte (2018), p. 336.
10. Brusatte (2018), p. 338.
11. Brusatte (2018), p. 198.
12. Brusatte (2018), p. 200.
13. Brusatte (2018), p. 204.
14. Brusatte (2018), p. 220.
15. Brusatte (2018), p. 219.
16. Everett, Daniel. (2017). How Language Began: The Story of Humanity’s Greatest Invention. Liveright Books. New York,p. 126.
17. Finlayson, Clive. (2010). The Humans Who Went Extinct. Oxford University Press. Oxford, UK, p. 99.
18. Hawks, John et al. (2000). “Population Bottlenecks and Pleistocene Human Evolution.” Molecular Biology and Evolution. January 1, 2000. Vol. 17. No. 1,p. 9.
19. Finlayson (2010), p. 99.
20. Yost, Chad et al. (2018). “Subdecadal Phytolith and Charcoal Records from ~74ka Toba Supereruption.” Journal of Human Evolution. March 2018. Vol. 116. p. 75–94.
21. Pinker, Steven. (2019). Enlightenment Now. Penguin Books. New York, p. 294.
22. Sterns, Beverly et al. (2000). Watching from the Edge of Extinction. Yale University Press. New Haven, CT, p. x.
23. Pinker (2019), p. 294.
24. Bertram (2016) provides a model to quantify this qualitative statement.
25. Scanes, Colin. (2018). Animals and Human Society. Academic Press, Elsevier. London, p. 84.
26. Papagianni, Dimitra. (2015). The Neanderthals Rediscovered. Thames & Hudson. London, p. 21.
27. Lee, Sang-Hee. (2015). Close Encounters with Humankind. W.W. Norton. New York, p. 176.
28. Lee (2015), p. 184.
29. Papagianni (2015), p. 13.
30. Reich, David. (2018). Who We Are and How We Got Here. Pantheon Books. New York, p. 26.
31. Diamond, Jared. (1999). Guns, Germs, and Steel. W.W. Norton. New York, p. 28, and Reich (2018), p. 28.
32. Harari, Yuval. (2015). Sapiens. HarperCollins. New York, p. 145, p. 145.
33. Christian (2011), p. 175.
34. Keeley, Lawrence. (1996). War before Civilization. Oxford University Press. Oxford, UK, p. 37.
35. LeBlanc, Steven. (2003). Constant Battles: Why We Fight. St. Martin’s Press. New York, p. 97.
36. Reich (2018), p. 40.
37. Stringer, Chris. (2012). Lone Survivors. Times Books. New York.
38. Shipman, Pat. (2015). The Invaders: How Humans and Their Dogs Drove Neanderthals to Extinction. Belknap Press. Cambridge, MA.
39. Stringer (2012), p. 204, Money, Nicholas. (2019). The Selfish Ape. Reaktion Books. London, p. 70.
40. Brannen (2017), p. 226–233 for the species humans have driven to extinction.
41. Diamond (1999), p. 204.
42. Brannen (2017), p. 240.
43. Money (2019), p. 97.
44. Brannen (2017), p. 238.
45. Walsh, Bryan. (2019). End Times. Hachette Books. New York, p. 149.
46. Christian (2011), p. 142.
47. Like a cat perched on the windowsill of a high-rise apartment building, we believe our survival is not at risk. “After all,” the cat may say to itself, “I have rested outside this open window for many years, peering down at the street fifty stories below, and nothing bad has happened.” Unfortunately, cats who fell to their death are not around to reconsider whether a narrow ledge 600 feet above ground level is the best place to nap.