The evolution of life requires a more or less precise balance between mutation and selection. If it is too low, new varieties will not be available to adapt to some future change in the environment. If the mutation rate is too high, we lose the inheritance of four billion years of painstaking evolution. Mutations might occur during replication if the enzyme DNA polymerase makes a mistake.

→ Evolution works through mutation and selection. → The secrets of evolution are death and time-the deaths of enormous numbers of lifeforms that were imperfectly adapted to the environment and time for a long succession of small mutations that were by accident adaptive, time for the slow accumulation of patterns of favorable mutations. Species appear, abide more or less briefly and then flicker out. The Earth used to be inhabited by plants and animals of which there is today no living trace. → Far more species have become extinct in the history of the Earth than exist today they are the terminated experiments of evolution. Perhaps there are many other planets that today have abundant microbes but no big beasts and vegetables. → Large lifeforms with specialized organs are hard to evolve. Some species arise and die out, some never evolve beyond its simplest forms. → Perhaps the origin and evolution of life is, given enough time, a cosmic inevitability. It implies the deep interconnectedness of all things. → Cosmos is a Greek word for the order of the universe. Understanding is a joy, knowledge is prerequisite to survival. Hopefully, will invest our energies in an enterprise devoted not to death but to life: the expansion of our understanding of the Earth and its inhabitants and the search for life elsewhere. Our explorations can be carried out only on behalf of all the people of the planet Earth. We are fortunate: we are alive we are powerful the welfare of our civilization and our species is in our hands. In rapid succession fishes, vertebrates, winged insects, amphibians, reptiles, dinosaurs, mammals, birds, cetaceans, primates, apes and humans appeared.

Since then exquisite new adaptations followed one another with comparatively breathtaking speed. Around 600 million years ago an enormous proliferation of new life forms emerged,called the Cambrian explosion. However, it’s important to keep in mind that far more species have become extinct in the history of the Earth than exist today. There might be abundant microbes on other planets, but no big beasts and vegetables. As far as we know, complex lifeforms with specialized organs are hard to evolve.

Cosmos carl sagan book