Legacy of An Impact

Sixty-six million years ago we finally got the break we needed to push on to where we are today.

It was a quiet, sunny June day at the edge of the sea on what we now call the Yucatan Peninsula at the edge of the Gulf of Mexico, a place we would have considered beautiful had we been there to appreciate it. While there were massive volcanoes erupting on the other side of the Earth, here the reptiles, birds, amphibians, and small mammals were concerned only about their next morsel of food or taking precautions that they would not be another creature’s midday meal. Behind the serene landscape of gingkoes, ferns, palms, cycads and other Cretaceous era plants, the rule was hunt and be hunted. The large carnivorous dinosaurs took what they wanted; the mammals, most of them no bigger than today’s opossums, took a few bites of whatever edible they could find then scurried back into the safety of their dens.

The sky darkened. For a few moments something as big as Earth’s largest mountain blocked the sun and shot through the warm, humid atmosphere at 16 miles per second. Animals that looked up and saw it did not have time to take cover. Those hit directly were the lucky ones. The asteroid, estimated to be over 6 miles in diameter, made a crater 110 miles wide and about 12 miles deep.

Within seconds of impact millions of tons of vaporized sulfur and molten rock fragments – tektites– were blown miles into the sky. While the sulfur mixed with oxygen to make toxic sulfur dioxide, tektites falling back through the Earth’s atmosphere were hot enough to start immense forest fires that produced enough smoke and soot to darken the sky for months.

Meanwhile, on the other side of the Earth in the land mass that is now central India, a large volcano spewed its own blend of deadly gases and molten lava into the atmosphere. The combination of cosmic bomb from above and fiery magma and ash from below created a time of global darkness when a large percentage of Earth’s light-dependent photosynthesis ceased, severely disrupting Earth’s food chain and leading to the death of some 70 percent of all life from large animals to ocean plankton and fish. Within weeks the carnivorous tyrannosaurs, the vegetarian titanosaurs, and all of the gigantic reptiles alive at that time died. They would not return.

Along with some fern spores that within a few years began re-greening Earth, among the 30 percent of species that survived this global holocaust were a few birds that did not depend solely on trees for nesting, enough crocodiles and turtles to keep those species of reptiles going, some sharks and their kin, several insect species, and a few small burrowing mammals whose offspring in time would profoundly change the Earth.

These small mammals, now free from dinosaur predation, no longer had to live surreptitiously. They wandered out of their dens, and feasted on the dead and dying animals that had once feasted on them. As they satiated themselves and were able to hunt more easily, the next several years saw them begin to grow both in population and size to the point that after the dust cleared and Earth returned to the warm, humid, fertile place it had been before the asteroid impact, mammals replaced reptiles as Earth’s dominate vertebrates.

As the geologic ages passed, a variety of species of mammals came and went. Predation, food supplies, and climate variations took their toll on a large number of species which for one reason or another were not able to adapt to variations in their environment. But many persevered and through genetic mutation or epigenetic heritable changes, were able to pass their genes on to future generations. Then about 20 million years after the momentous meteor had removed their reptilian nemesis, a group of mammals that had survived their environmental challenges branched off to form catarrhines, a division of African primates that became our earliest direct ancestors. These were some of the first mammals that had flat fingernails and toenails rather than claws. Also, they did not have prehensile tails like other monkeys.

Perhaps one of the most important of the physical traits that tied them to later apes and chimpanzees, and eventually to humans, was that their nostrils were close together and faced downward instead of sideways. This anatomical feature that separated them from monkeys found in the western hemisphere, gave them the name catarrhine which comes from the Greek words katar and rhein meaning to flow down. Monkeys in South America were called platyrrhines because their nostrils were spread apart and pointed sideways. Another difference was that Catarrhines were more terrestrial, a trait which became important in the development of hominins, that line of primates who became the ancestors of modern humans. Proto humans, with their catarrhine noses and tailless bodies, were just around the corner, at least evolutionarily speaking.

Natural selection began haphazardly designing what would eventually become human beings through one morphological configuration after another. Brains grew bigger and bodies changed as we evolved from four-legged tree dwellers to into two-legged ground walkers. For thousands of years various hominin groups, as they split off from their primate ancestors, adapted to the opportunities and restrictions of their environment or they perished and made room for those whose powers of reasoning and tool-making skills kept their evolution progressing.

The ones who eventually became the ancestors of everyone living on Earth today persevered through trial and error, successes and failures, adopting those behaviors which enhanced their chances for survival and eliminated those that did not. For example, as climate change in Africa a few million years ago caused the decline of forests and an increase of grassy savannas, proto humans became aware of the benefits of coming down from the trees and standing upright on the ground. In open spaces it was obviously better to stand up straight and walk on two legs since they could see farther than their bent over quadrupedal cousins. This behavior also freed their front feet to evolve into very useful tool-making and weapon-carrying hands. At this time, our ancestors were also learning to rely more on vision and less on smell to comprehend what was around them.

The fossil record suggests that possibly one of our first ancestors to become at least partially bipedal was a hominin called Orrorin tugenensis who came in and out of evolution as far back as 6 million years ago in Kenya. Then around 4.4 million years ago we had Ardipithecus ramidus whose bones were found in Ethiopia. Ardi, like Orrorin, could both climb trees and walk upright on the ground, making them nimble hominins indeed. Then, Lucy, an Australopithecus afarensis hominin, came along some 3.2 million years ago in Ethiopia. Her bone structure indicates that she usually walked upright but she still had long arms for climbing and a small cranial cavity like her ape ancestors. Taung Child, a 3-million-year- old girl discovered in South Africa also had a bone structure that gave evidence of bipedalism. Yes, we were still primates, but we were coming down out of the trees and learning to run around the countryside.

While we were learning to walk upright, we were also learning to think. But it was not until Homo habilis (handy man) who bipedaled around the Olduvai Gorge in northern Tanzania 2.5 to 1.8 million years ago, that the fossil record shows evidence of a slightly larger cranial cavity than in the older Australopithecus fossils. Habilis, who some anthropologists consider to be a transition hominin between Australopithecus and Homo, was probably the first to make rudimentary stone tools and was certainly a ground dweller who did not spend as much time in trees as many of his primate ancestors had done. And with a cranial capacity of around 600 cubic centimeters, habilis was nearer modern humans than his chimpanzee ancestors with their 400 cubic centimeter brains. Like chimpanzees, however, this early hominin still lived primarily in extended family groups and would occasionally participate in group hunting excursions or join with others to defend his kin against intruders.

There were tradeoffs as we evolved more human-like characteristics. One was that as we lost our ability to climb trees, we evolved the ability to run and chase our prey or escape from it when necessary. Also, since we no longer had large, sharp canine teeth for biting our enemies, we had to devise other ways to defend ourselves. Thus, it became necessary to make tools and weapons out of the sticks, rocks and bones around us.

As our brains grew, our ability to more precisely design and fashion stone and bone tools from sewing needles to spear points and hammers became more sophisticated. We became better at envisioning the shape of the tool we wanted for a specific purpose. And very importantly, our manual dexterity was aided by the development of our unique ulnar opposition. Our thumb evolved to became more agile than the thumbs of early primates and we became able to touch all of our fingers together. This physical trait strengthened our grip and greatly enhanced our ability to make and use tools.

Around two million years ago Homo erectus (upright man) showed up and introduced the world to the use of fire and more complex tools. These hominins were more social than their ancestors and probably were the first to live in semi-permanent hunter-gatherer societies. They marked another great transition in human evolution in that living with others in groups larger than family and kin is believed to have brought about the concepts of symbiotic cooperation, empathy, and caring for the old and injured.

Homo erectus was a successful hominin who spread from the valley of Lake Turkana in Kenya out across Eurasia as far west as Spain as far east as Indonesia. It is believed that they lasted from over 1 million years ago to around 100,000 years ago. Some scientists consider Homo erectus to be a direct predecessor of other lineages whose fossils show greater brain size and manual dexterity such as Homo heidelbergensis and Homo ergaster.

One of the first homo erectus fossils was found in the 1890s in Java. Now known as Java Man, this hominin is thought to have lived between 700,00 and 1 million years ago. These early humans had traveled many miles from Africa in just a few thousand years, probably following herds of migrating animals. With a brain that was now around 900 cubic centimeters in size, we were becoming thinking and reasoning proto humans who were learning to live together and care for each other, and possibly even communicating by a rudimentary language. And, incidentally, their faces were becoming more like modern humans in that Homo erectus was the first hominin to develop a protrusion below the mouth that became our modern chin.

A number of hominin lineages continued to diverge and separate, until around 300,000 years ago our closest human ancestor, Homo sapiens (intelligent man) evolved in North Africa. As the species migrated to various parts of the Earth, offshoot groups such as Cro-Magnon, first found in France, Skhul, first found in Israel, Neanderthal, first found in Germany, and others added their skills and wisdom to the growing genetic evolution of humanity.

It is interesting that today there is some debate as to whether these various pre-human lineages as far back as Australopithecus were different species or just variations of the one hominin species that we today call Homo sapiens. It could be argued that as we evolved from primates, each lineage tended to build upon the older ones as far as dexterity, brain size, and sociability, which would indicate a continuation of one species. On the other hand, some anthropologists feel that the fossil record shows that each lineage was different enough from others to be considered a separate species. Perhaps before long, precise DNA testing will shed some light on the ‘one species’ or ‘many species’ question.

Whether we are the offspring of one species or many, the meteor impact which ended the reign of the dinosaurs that had ruled Earth for over 165 million years gave us the freedom to evolve. Today, our stalwart species, spawned in the highlands of central Africa, inhabits every corner of the Earth. Although the morphology of our bodies has not changed much in the last 40,000 years or so, our understanding of who we are and our social obligations to each other continue to evolve.

Yet, even as our human consciousness matures, we still seem to be strongly influenced by the kill or be killed instincts of the animals we evolved from. It should be obvious that symbiotic cooperation will sustain us, whereas animosity and belligerency will not. So why do we not put the old animal instincts behind us? We seem to be caught in a kind of psychosis stifling our maturation process that, so far, we have not been able to rise above.

Yet, let us hope that finally, after all these years of religions, philosophies, political factions, wars, cycles of sanity and insanity we are coming to the point in our human journey where we are beginning to realize that as we become more able to control our own evolution, we can reach the next level in our ability to live harmoniously with each other. We can become Homo ethicus, the next stage of our evolution beyond Homo sapien, a more socially and emotionally developed human who is better able to use the intelligence we have accumulated over millions of years of trial-and-error learning and surviving to lead us toward a world free of greed, free of political conflict, religious conflict, racial conflict, and free of the fear that drives us to make weapons and start wars with no other purpose than to destroy ourselves.

The Anthropocene is our time in Earth’s history. Unlike our primate ancestors, we are shaping the world to suit our needs. We are curious, industrious, and creative. We have built great cities to live in and powerful rockets to take us to places our ancestors stared at in wonder but could not comprehend. But will we last as long as our reptilian predecessors? We have been evolving for millions of years, yet we’ve been Homo sapiens only a few thousand of those years. Evolutionarily speaking, we’re still the young kid in the neighborhood. Squirrels and butterflies, for example, have been around much longer than we have.

We have learned to learn, and that ability is our greatest asset, our greatest achievement. We have learned to live in nearly every environment on Earth. If we survive as a species, we will eventually learn how to live on other planets. The question confronting us, however, is have we learned enough to keep ourselves alive going into an unknown future? Have we acquired the brain power to stop being the victims of our weaknesses? In spite of our refined ability to plan ahead, we still find it too easy to act impulsively before thinking about the long-term repercussions of our actions. It is too easy to get caught up in polarizing politics, religious dogmas, and hateful biases that divide us into antagonistic factions.

Would it not be the height of irony that if we humans, who as far as we know, are the only Earthly creatures who have ever had the ability to control their own destiny, killed ourselves off because we lost control of the things that make us human, such our empathy, our caring for each other, and our ability to symbiotically cooperate for the betterment of everyone?

Yet, there have been many in our human history, as there are many now, who put their greed, and their personal ambitions ahead of the well-being of others. They are holding us back. And there are even some who are so obsessed with their lust for power they are willing to destroy much of the world to get their way. We will never be wholly human until that selfish attitude disappears from our thinking.

In the early 1950s when the cold war between the United States and Russia was prompting these nations and others to build nuclear arsenals, Albert Einstein wrote: “I do not know how WWIII will be fought, but WWIV will be fought with sticks and stones.” It was a frightening assessment of the political chaos spreading through the world at that time. And, unfortunately, after many decades of negotiation between nations, our world is still not any safer, and many would argue that due to such things as economic instability and nuclear proliferation, it is even less safe now than a few years ago.

While we are justified in celebrating our successes in technology, medicine and other important fields, we need to look with caution at our political, religious, and cultural differences that if not tightly controlled could set our human successes back thousands of years. We are a very young species still learning how to live peacefully with each other. We still have a lot to learn.

We have produced profound philosophies, worshiped a plethora of imagined gods to assuage our fear of the unknown, and experimented with various political systems. We have tried to rise above the chaos brought on by our greed and lust for power. So far none of our noble attempts have convinced strong leaders not to invade their weaker neighbors, or stopped robberies, or murders. It is a sad accounting that much of our history is a record of one cruel behavior after another. Will we ever get human life right? Will our deadly asteroid turn out to be ourselves? Is the sky already darkening?