Secrets of Evolution

Secrets of Evolution

The secrets of evolution are death and time.

The death 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. Part of the resistance to Darwin and Wallace derives from our difficulty in imagining the passage of the millennia, much less the aeons. What does seventy million years mean to beings who live only one-millionth as long& We are like butterflies who flutter for a day and think it is forever.

What happened here on Earth may be more or less typical of the evolution of life on many worlds; but in such details as the chemistry or proteins or the neurology of brains, the story of life on Earth may be unique in all the Milky Way Galaxy.

The Earth condensed out of interstellar gas and dust some 4.6 billion years ago. We know from the fossil record that the origin of life happened soon after, perhaps around 4.9 billion years ago, in the ponds and oceans of the primitive Earth.

I hope the extraterrestrials remember how frail humans are (quotations from Megan Jorgensen). Image Virtual Worlds Old Painting Style by © Megan Jorgensen

The first living things were not anything so complex as a one-celled organism, already a highly sophisticated form of life. The first stirrings were much more humble. In those early days, lightning and ultraviolet light from the Sun were breaking apart the simple hydrogen-rich molecules of the primitive atmosphere, the fragments spontaneously recombining into more and more complex molecules.

The products of this early chemistry were dissolved in the oceans, forming a kind of organic soup of gradually increasing complexity, until one day, quite by accident, a molecule arose that was able to make crude copies of itself, using as building blocks other molecules in the soup.

About two-thirds of the mass of the human brain is in the cerebral cortex, devoted to intuition and reason. Humans have evolved gregariously.

How would we explain the global arms race to a dispassionate extraterrestrial observer? How would we justify the most recent destabilizing developments of killer-satellites, particle beam weapons, lasers, neutron bombs, cruise missiles, and the proposed conversion of areas the size of modest countries to the enterprise of hiding each intercontinental ballistic missile among hundreds of decoys? Would we argue that ten thousand targeted nuclear warheads are likely to enhance the prospects for our survival? What account would we give to our stewardship of the planet Earth?

Four billion years ago, the Earth was a molecular Garden of Eden. There were as yet no predators. Some molecules reproduced themselves inefficiently, competed for building blocks and left crude copies of themselves.

Every lifeform on Earth has a different set of instructions, written out in essentially the same language. The reason organisms are different is the differences in a nucleotide, copied in the next generation, which breeds true.

Since mutations are random nucleotide changes, most of them are harmful or lethal, coding into existence non-functional enzymes. It is a long wait before a mutation makes an organism work better. An yet it is that improbable event, a small beneficial mutation in a nucleotide a ten-millionth of a centimeter across, that makes evolution go.

With reproduction, mutation and the selective elimination of the least efficient varieties, evolution was well under way, even at the molecular level. As time went on, the molecules got better in reproducing. Those with specialized functions eventually joined together, making a kind of molecular collective – the first cell. Plant cells today have tint molecular factories, called chroloplasts, which are in charge of photosynthesis – the conversion of sunlight, water and carbon dioxide into carbohydrates and oxygen. The cells in a drop of blood contain a different sort of molecular factory, the mitochondrion, which combines food with oxygen to extract useful energy. These factories exist in plant and animal cells today but may once themselves have been free-living cells.

By about three billion years ago, a number of one-celled plants had joint together, perhaps because a mutation prevented a single cell from separating after splitting in two. The first multicellular organisms had evolved. Every cell of your body is a kind of commune, with once free-living parts all banded together for the common good. And you are made of a hundred trillion cells. We are, each of us, a multitude.