For every living being, from a bacteria, to a Blue whale, life begins at birth, grows with food, reproduces at maturity, and dies to become nutrients for the whole from which it came. This is called The Circle of Life. Elton John sang about it in Disney’s The Lion King, as many remember. It’s actually a very lovely song. Despite the sentimental mucking about with something of such vital importance to Biology, the lyrics are correct: "...the sun rolling high, through the sapphire sky, keeps great and small on the endless round." The sun is Earth's source for all photosynthesis, and thereby too, the nutrients for all herbivores, carnivores and fuel users.
The central theme of that movie is that all living things must contribute to the greater good for life to continue in “the great Circle.” And also not lost on most viewers is the message that all beauty, grace, grandeur and wonder is found in belonging to the great circle.
Before the advent of monotheism, most culture’s recognized the cycles of seasons and the circular movements of orbiting bodies. They surmised, correctly, that life moves in repeating circles, as do seasons. Circles, and calendars marking them, became sacred in many ancient religions and calling a circle nearly always refers to addressing the four winds and directions, and acknowledging four elements that are central to life: Earth, Air, Water and Fire. At Stonehenge, and even far more ancient sites, circles were erected to honor not just the advent of the seasons, but the vital movements of sun, moon and stars that affect what lives, grows and dies, such as migratory animals and crops. Most monuments are oriented in precise ways to do astronomical charting, and catch light of each year's solstice in mid winter and mid summer.
In human lives, people speak of the reproduction urge, called Eros, and the death wish, called Thanatos. Both of these mark the beginnings of each circle of life, and of course, each life’s demise. In between are the central drives of every life to find food and to reproduce. Of course, not all humans do reproduce, but the urge to do so, sex appeal, is fundamental to what each genetic code instructs each organism to do.
In modern times, people have alienated nature to the point where they do not always honor the vital contribution of all living beings that sustain life on Earth. The hectic, crowded, modern world is often quite disconnected to the human animals ancient, powerful and necessary belonging to the rest of the circle of life.
The environmental movement, really quite young in industrial times, (but in ancient times quite the norm) suggests and celebrates that human beings are truly part of the great circle of life. Each being takes from Earth what is needed to live, and each being (supposedly) gives back by being food for the grass, micro and macro organisms that in turn create more life to continue the cycle. In human terms, often humans unfortunately fill their corpses with toxins and preservatives, so many centuries pass before they can return fully to the whole that gave birth to them.
Despite what singing lions may say, the circle of life is every bit as dependent upon hyenas as it is upon grass, lions, wildebeest and more. Like lions, (anthropomorphized in the Lion King), humans are hung up on hierarchy in unhealthy ways that leads them to dominate and exploit other organisms even to their own peril. Sustainability is simply a summarizing word that means humans must seek to find ways to preserve living systems by providing all the resources that are needed to keep the circle of life turning. As Earth is finite, people are now innovating ways to make quality of life sustainable.
In their temporary middle teen epoch rebellion against nature, people tried to find ways to take more than they could give back. But this is necessarily short lived, as systems will collapse, combust, or be burned out in resulting droughts, famines and plagues as people are now experiencing worldwide.
By borrowing from the future in converting stored carbon to fuels, humans inadvertently began to warm the planet. In over breeding, hunting, harvesting, mining and deforestation, people have sought to dominate and found themselves imperiled due to over stepping natural boundaries. In a basic way, human beings devised ways of exploiting other living resources and systems which now people must find a way to reverse. Sadly, for example there are millions of humans to every lion. The knowledge that there is no such thing as a free lunch has finally come full circle to the curious race known as humans.
Thankfully, however, the human race seems to have gotten an inkling about their transgressions early enough that they can learn better ways to protect, preserve and live with living systems. Alternative energy sources, improved farming and controlling reproduction are just some of the ways that people can rejoin and thus regain their rightful place in the circle of life.