Before commencing an account of how our worldviews evolved over the course of human history, I want to orient us in terms of an evolutionary timeline and summarise what we know of our ancestral forbears.
We are members of the species homo sapiens,
of the genus homo,
in the family of hominids (or hominidae)
in the order of primates,
in the class of mammals.
67 million years ago, the first family of primates emerged from mammals and, over millions of years, evolved into many different species throughout the Eurasian continent. Distinguished by their opposing thumbs and big toes, they were forest dwellers who lived extensively in trees. One of these was Ida – about the size of a cat and looking somewhat like a modern lemur – who lived c. 47 million years ago and whose fossilized remains were discovered in 1983 in Germany
43 million years ago, these early primates diversified into anthropoids (leading eventually to monkeys, apes, and humans) and prosimians (leading to lemurs, lorises, and tarsiers).
37 million years ago, the anthropoids diversified into New World and Old World monkeys, with the latter marking the first arrival of primates in Africa. One of these, known as “the Dawn Ape”, who lived in Egypt 35-33 million years ago, was a fox-sized anthropoid with an anatomy and teeth that would later characterise fully developed apes.
25 million years ago, apes diversified from Old World monkeys. One of the earliest of these, named Proconsul, appeared in the fossil record in Kenya. With no tail, a weight of 84 lbs, and a brain capacity of 150 cc, he was the predecessor of all the later great apes.
20 million years ago, the great apes began to disperse around the world. Those that went east into Asia evolved into the gibbon and later the orang-utan. Those that stayed in Africa evolved still later (9 million years ago) into gorillas, and then (5-6 million years ago) into hominids, chimpanzees and bonobos. Given our relatively recent common ancestry, it is not surprising that humans are 98.4% genetically the same as chimps. In fact, there is more difference between a zebra and a horse, or between a dolphin and a porpoise, than there is between you and a modern chimpanzee.
A particularly dry spell in Africa at that time appears to have driven some tree-dwelling apes out of the forest and into the grasslands, to which they adapted by standing upright on two legs, learning to hunt other mammals, and gradually developing bigger brains. These were the hominids, among whom the dominant species (from 4.1 to 1.9 million years ago) were the australopithecines. They consisted of half a dozen species that lived in Kenya, Tanzania, and Ethiopia, with enough brainpower to live in groups of up to 70.
One of these was the now-famous Lucy – a 3.18 million year old australopithecine whose remains were found in Ethiopia in 1974. A three-year-old girl, 3 ½ feet tall, she was bipedal and a good climber, but her brain size was only slightly larger than that of a chimpanzee. Her shoulder blades resembled a young gorilla’s, as did the hyoid bone in the throat, suggesting that speech had not yet begun to evolve. Two years later, in Tanzania, Mary Leakey found footprints from two individuals from the same family of hominids, dated to 3.6 million years ago
The African Rift Valley stretches for 2000 miles from Ethiopia in the north to Malawi in the south. It was here that the first species of the homo genus – homo habilis – made its appearance some 2.5 million years ago, probably evolving from a smaller-brained australopithecine. The still larger-brained homo erectus emerged some 500,000 years later, and our own species, homo sapiens, with a brain 50% larger again, emerged 200,000 years ago.
We do well, I think, to remember our origins – and, with an appropriate measure of humility, recognise that this big-brain experiment in self-awareness has been in operation for not much more than the twinkling of an eye. If we shrink the evolution of life on this planet to a time-span of just one year, homo sapiens has been here since only 26 minutes before midnight on New Year’s Eve. Even our australopithecine forbears survived 10 times longer than that before they became extinct, and our chimpanzee cousins have been around for 30 times as long. We should only be so lucky!
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