Cambrian Explosion and Our Ancestors

Cambrian Explosion and Our Ancestors

Before the Cambrian explosion species seem to have succeeded one another rather slowly. In part this may be because the richness of our information declines rapidly the farther into the past we peer; in the early history of our planet, few organisms had hard parts and soft beings leave few fossil remains. But in part the sluggish rate of appearance of dramatically new forms before the Cambrian explosion is real; the painstaking evolution of cell structure and biochemistry is not immediately reflected on the external forms revealed by the fossil record.

Soon after the Cambrian explosion, the oceans teemed with many different forms of life. By 500 million years ago there were vast herds of trilobites, beautifully constructed animals, a little like large insects. Some hunted in packs on the ocean floor. They stored crystals in their eyes to detect polarizes light. But there are no trilobites today; there have been none for 200 million years. The Earth used to be inhabited by plants and animals of which there is today no living trace. And of course every species now on the planet once did not exist. There is no hint it the old rocks of animals like us. Species appear, abide more or less briefly and the flicker out.

There is always hope. Illustration by Elena

After the Cambrian explosion, exquisite new adaptations followed one another with comparatively breathtaking speed. In rapid succession, the first fish and the first vertebrates appeared; plants, previously restricted to the oceans, began the colonisation of the land; the first insect evolved, and its descendants became the pioneers in the colonisation of the land by animals; winged insects arose together with the amphibians, creatures something like the lungfish, able to survive both on land and in the water; the first trees and the first reptiles appeared; the dinosaurs evolved; the mammals emerged, and then the first birds; the first flowers appeared; the dinosaurs became extinct; the earliest cetaceans, ancestors to the dolphins and whales, arose and in the same period the primates – the ancestors of the monkeys, the apes and the humans.

Less than ten million years ago, the first creatures who closely resembled human beings, evolved, accompanied by a spectacular increase in brain size. And then, only a few million years ago, the first true humans emerged.