Earth has a long and rich history that dates back to at least 4.5 billion years ago. Currently, there are well over one-and-a-half million known species in existence. Scientists believe there may be as many as another 80 million or so to discover. Yet this number pales compared to the total number thought to have existed — 40 billion — which are now extinct. The story of humankind is truly wondrous and amazingly recent in geologic times.

In 1758 the Swedish botanist Carl Linnaeus named humans Homo sapiens or “knowledgeable man.” We are social animals that enjoy music, humor, literature and affection. We are also supreme game players and actually cherish the art of finesse.

Humans are 98.8 percent genetically similar to chimpanzees and bonobos. Deep down, however, we do not like the idea that we are related to the apes, monkey or Neanderthals and at times we’ll go to extreme lengths to distance ourselves. Sometimes humans are too full of hubris or ignorance, or worse, a combination of both.

In fact, the earliest primates are thought to have evolved from Purgatorius, a small insectivore-like, forest-dwelling mammal, in the late Cretaceous period, over 70 million years ago. The oldest known human-related fossil — Sahel Man from Chad — dates back 7 million years. The next oldest fossil is 4.4 million years old, and it was found 1,553 miles away from Chad in Middle Awash, Ethiopia.

The most intact fossil dating back 3.5 million years, found in 1974 by Don Johanson, was named Lucy. She walked upright or bipedal rather than knuckle-walking, a strange quadrupedal gait seen in chimps and gorillas. Upright walking was significant for it freed hands and enabled another crucial step in hominid evolution — tool making. Other known tool-makers in the animal kingdom include ants, crows, elephants, dolphins and ravens.

Pollen grains and fossil animal teeth from Africa clearly show that during the mid to late Pliocene (3 to 4 million years ago) the climate changed significantly from moist and warm to arid and cool. Forests and clumps of trees or woodlands retreated or died off and Savannah grasses and drought and cold tolerant species predominated.

Climate change had a profound effect on human-related ancestry. It forced many of them to leave the forest and challenged them to make a living on grasslands.

Stone tools enabled the development of nut-cracking technology and it provided bipedal hominids with a highly nutritious supply, in excess of 5,000 calories a day, of proteins. Increased intake of proteins paved the way for the development of larger brains greater than 600 cubic centimeters. The earliest stone tools date back to 2.6 million years ago.

About 2.2 million years ago Earth entered into the Pleistocene Epoch, which is renowned for long periods of glaciation interspersed by much shorter, 12,000- to 26,000-year, warm periods. Incidentally, we are currently in a short warm period called the Holocene. The onset of glaciation a couple million years ago is believed to have increased the hunting skills of early hominids. Diets were much higher in protein from the copious amounts of mega Ice Age mammals and this subsequently helped the size of brains to double and in some cases almost triple. 

Roughly 1.8 million years ago human ancestors started leaving Africa. It was a remarkable feat, but it is, of course, no more remarkable than similar migrations by successful species since the days of the dinosaurs. Even at a rate of 6,000 miles per generation, of say, 20 years — a species could easily cover 31,000 miles in 10,000 years. North American caribou migrate some 3,100 miles every year. 

Five-hundred-thousand years ago the hominid brain size jumped to 900 cubic centimeters. And this coincided with the rise of the Neanderthals in Eurasia. They were excellent hunters and tool-makers who lead strenuous and dangerous lives. Eighty-thousand years ago they invented strong bonding glue from birch tree pitch. Mysteriously, Neanderthals went extinct 28,000 years ago. 

Fossils from coastal Blombos Cave, South Africa 80,000 years ago revealed a diverse array of bone tools including projectiles, awls and crayons. Awls were important because they enabled furry skins to be sewn thus providing warmth during cold periods. Seven centimeter-long, intentionally scored rocks with a series of lines making diamond patterns were covered in iron-rich ochre and used as crayons in cave art.

The greatest collection of cave art is found in Chauvet in southern France which 32,000 years ago was an Ice Age game park of Europe. Equally magnificent Australian rock art dating back to 24,600 years ago depicts a number of techniques including carving, pecking and spray painting.

The emergence of language probably from manual gesticulation some 200,000 years ago was a major step in human evolution. The human larynx descends into the vocal tract enabling an astounding range of vowels and consonants that can be strung together without conscious effort to form complex communications. Fossil evidence from 60,000 years ago shows that Neanderthals were also capable of advanced vocalization including speech. Today there are over 6,000 spoken languages.

Cro-Magnon, the direct descendants of modern man, appeared about 130,000 years ago. Ninety-thousand years ago they reached Mount Carmel (in today’s Israel). Cro-Magnon arrived in Australia 56,000 years ago and 4,000 years later they reached Europe. Paleo-humans crossed the Bering land bridge about 20,000 years ago and reached South America roughly 5,000 years later. By 1500 A.D. the population was 47 million. Today there are over 6.8 billion people on Earth.

Out of the long march of Africa, all living humans, whether Asian, African or European extraction share 99.9 percent of the 26,000 genes or so in our genome. Our molecular make-up has about double that of the fruit-fly (13,600 genes) and yet half that of a poplar tree (45,000 genes).

At least six species of humans have existed over the past 2 million years or more; we are the sole survivors.


Dr. Reese Halter is a conservation biologist at Cal Lutheran University, public speaker and founder of the international conservation institute Global Forest Science. His most recent children’s book is “Mysteries of the Redwood Forest with Bruni the Bear.” Follow him: