From flying robot insects to running robot dog to humanoids such as the world’s first robot citizen Sophia, artificial life forms are populating the planet Earth; and some people are bound to find artificial life forms more attractive than natural life forms.

Intelligent life on a planet comes of age when it first works out the reason for its own existence.

I must mend the ways of my mind. This is a very big place, and I do not know how it works. I am a member of a fragile species, still new to the earth, the youngest creatures of any scale, here only a few moments as evolutionary time is measured, a juvenile species, a child of a species. We are only tentatively set in place, error prone, at risk of fumbling, in real danger at the moment of leaving behind only a thin layer of our fossils, radioactive at that.

<nowiki>[</nowiki>Martin Rees] may be right. If we were to go back 5 million years, as intelligent apes, and ask ourselves "What is postbiological life?" I think the answer is it's not a concept that would possibly mean anything. So we've had... 4 billion years of life on earth, and it's come up with an enormous wealth and variation, but it's all organic and... the chances of it coming up with humans? I can't put a number on that. ...I don't think there's an inevitability that life, once it's started will give rise to a human-like intelligence or beyond that. I think there's nothing inevitable about it, and if we just go back a few million years on earth, there was nothing inevitable about it. So I, personally would still look for organic life, but... I'm not sure that would be the easiest thing to find. It may be that it's easier to find, yes, nano aliens or something.

Over the years, as I listened to the engineering give-and-take over the question of artificial life-forms, I kept coming up against something obdurate inside myself, some stubborn resistance to the definition of “life” that was being promulgated. It seemed to me too reductive of what we are, too mechanistic. Even if I could not quite get myself to believe in God or the soul or the Tao or some other metaphor for the ineffable spark of life, still, as I sat there high in the balcony of the Stanford lecture hall, listening to the cyberneticists’ claims to be on the path toward the creation of a sentient being, I found myself muttering, No, that’s not right, we’re not just mechanisms, you’re missing something, there’s something else, something more. But then I had to ask myself: What else could there be?

If the Earth were as old as a person, a typical organism would be born, live and die in a sliver of a second. We are fleeting, transitional creatures, snowflakes fallen on the hearth fire.

But if you are going to claim, as humans do, to be superior to all life forms, past and present, then you must gain an understanding of the oldest living organisms on earth who were here long before you arrived and will still be here after you have gone.

There might be very primitive life in our solar system — single-cell animals, that sort of thing. We may know the answer to that in five or ten years. There is very likely to be life in other solar systems, in planets around other stars. But we won't know about that for a long time.

The animate environment has been the most formidable factor in the evolution of mundane life. The inanimate has been indifferent. The animate has not been so. It has been relentless. While the ages were yet tender, life began to riot upon life, and it has continued to do so to this moment. Where the inanimate has slain and selected one, the animate has slain multitudes. It is estimated that the life process is now about twenty millions of years old. Its existence has been one unbroken bacchanal of blood. Aggregate has preyed upon aggregate and species has decimated species. Tides of irresponsibles have swept over the continents and thru the deeps, collided, grappled, and exterminated each other. What is hidden in the horrible chasm between monera and man, no fancy will ever illume. It is the mighty charnal of creation. The skeletons of two millions of exterminated species of living beings are there with all their unimaginable accompaniments—wars, blacknesses, frightful manglings, eclipses, horrible concussions, inextinguishable malignities, hell.

From the paramecium to the human race, all life forms are meticulously organized, sophisticated aggregates of evolving microbial life. Far from leaving microorganisms behind on an evolutionary "ladder," we are both surrounded by them and composed of them. Having survived in an unbroken line from the beginnings of life, all organisms today are equally evolved.

Was there to be any end to the gradual improvement in the techniques and artifices used by the replicators to ensure their own continuation in the world? There would be plenty of time for improvement. What weird engines of self-preservation would the millennia bring forth? Four thousand million years on, what was to be the fate of the ancient replicators?

They did not die out, for they are past masters of the survival arts. But do not look for them floating loose in the sea; they gave up that cavalier freedom long ago. Now they swarm in huge colonies, safe inside gigantic lumbering robots, sealed off from the outside world, communicating with it by tortuous indirect routes, manipulating it by remote control.

They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.

For the hundreds of thousands of years of human existence when technologies were simple or non-existent, this may have had little impact on human life and the earth that sustains it. Each generation of hunters and gatherers, then plowmen and pioneers, passed on tools to the next generation to help them survive. Change from one generation to the next was slow and hardly noticeable. In those days there was little understanding of science and how things worked, and explanations were not scientific.

Artificial Life [AL] is the study of man-made systems that exhibit behaviors characteristic of natural living systems. It complements the traditional biological sciences concerned with the analysis of living organisms by attempting to synthesize life-like behaviors within computers and other artificial media. By extending the empirical foundation upon which biology is based beyond the carbon-chain life that has evolved on Earth, Artificial Life can contribute to theoretical biology by locating life-as-we-know-it within the larger picture of life-as-it-could-be.

Without the legions of minuscule organisms that have preceded us over the ages and whose descendants surround us and support us still, life as we know it could not exist.