Shadows of Forgotten Ancestors

By 3 billion years ago, life had changed the color of the inland seas; by 2 billion years ago, the gross composition of the atmosphere; by 1 billion years ago, the weather and the climate; by a third of a billion years ago, the geology of the soil; and in the past few hundred million years the close-up appearance of the planet. These profound changes, all brought about by forms of life we tend to consider “primitive,” and of course by processes we describe as natural, mock the concerns of those who hold that humans, through their technology, have now achieved “the end of Nature.” We are rendering many species extinct; we may even succeed in destroying ourselves. But this is nothing new for the Earth. Humans would then be just the latest in a long sequence of upstart species that arrive on-stage, make some alterations in the scenery, kill off some of the cast, and then themselves exit stage-left forever. New players appear in the next act. The Earth abides. It has seen all this before.

Life has penetrated only a thin surface layer, bounded by the heavens above and something very much like hell below. The planet itself—rotating once a day, revolving about the Sun once a year, circumnavigating the center of the Milky Way Galaxy once every quarter billion years, this world of rock and metal with its deep convection currents that make and destroy continents and generate the planet’s magnetic field—the planet knows nothing of life. The Earth would continue on its way as readily without life as with it. The Earth is indifferent, and all but that shallow clement zone at its very surface is impervious to anything life has been able to serve up.

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Our family tree was rooted when the Earth was just emerging from a time of massive, obliterating impacts, molten red-hot landscapes, and pitch-black skies; when the oceans and the stuff of life were still falling in from space; when our connection with the Universe around us was manifest. The orphan’s file began in epic style.

The family tree of a few rare individuals of our species, we’ve argued, can be traced back perhaps as much as two or three dozen generations. Most of us, in contrast, are able to penetrate only three or four generations into the past before the record fades and is lost. With a rare exception here and there, all earlier ancestors are the merest phantoms. But hundreds of generations link us to the time that civilization was invented, thousands of generations run to the origin of our species, and a hundred thousand generations lie between us and the first member of the genus Homo

. How many generations link us back through our non-human primate, mammal, reptile, amphibian, fish, and still earlier ancestors to the microbes of the primeval sea, and how many generations before that to the first organic molecules able to make crude copies of themselves is unfathomed—but it might approach 100 billion. The family tree of each of us is graced by all those great inventors: the beings who first tried out self-replication, the manufacture of protein machine tools, the cell, cooperation, predation, symbiosis, photosynthesis, breathing oxygen, sex, hormones, brains, and all the rest—inventions we use, some of them, minute-by-minute without ever wondering who devised them and how much we owe to these unknown benefactors, in a chain 100 billion links long.

Many have construed our clear kinship with the other animals as an affront to human dignity. But any one of us is much more closely related to Einstein and Stalin, to Gandhi and Hitler than to any member of another species. Shall we think more or less of ourselves in consequence? The discovery of a deep connection between human nature, all of human nature, and the other living things on Earth comes not a moment too soon. We are helped to know ourselves.

In acknowledging our ties of kinship, we are forced to reconsider the morality (as well as the prudence) of our conduct: wiping out another species every few minutes, night and day, all over the planet. Over the last few decades we have caused the extinction of something like a million species—some providing potential new foods, some desperately needed medicines, but all unique DNA sequences, tortuously evolved over 4 billion years of the evolution of life and all now lost forever. We have been faithless heirs, squandering the family inheritance with little thought for the generations to come.

We must stop pretending we’re something we are not. Somewhere between romantic, uncritical anthropomorphizing of the animals and an anxious, obdurate refusal to recognize our kinship with them—the latter made tellingly clear in the still-widespread notion of “special” creation—there is a broad middle ground on which we humans can take our stand.