DURING the summer of 1940, I was an 11-year-old living with my family in a low-income apartment in Washington, D.C. We were within easy walking distance of the National Zoo and an adjacent strip of woodland in Rock Creek Park. I lived most of my days there, visiting exotic animals and collecting butterflies and other insects with a net that I had fashioned from a broom handle, coat hanger and cheesecloth. I read nature books, field guides and past volumes of National Geographic. I had already conceived then of a world of life awaiting me, bottomless in variety.

Seventy-six years later, I have kept that dream. As a teacher and scientist I have tried to share it. The metaphor I offer for biological diversity is the magic well: The more you draw, the more there is to draw.

But today the dream is at risk. Civilization is at last turning green, albeit only pale green. Our attention remains focused on the physical environment — on pollution, the shortage of fresh water, the shrinkage of arable land and, of course, the great, wrathful demon that threatens all our lives, human-forced climate change. But Earth’s living environment, including all its species and all the ecosystems they compose, has continued to receive relatively little attention. This is a huge strategic mistake. If we save the living environment of Earth, we will also save the physical, nonliving environment, because each depends on the other. But if we work to save only the physical environment, as we seem bent on doing, we will lose them both.

So, what exactly is the current condition of the living environment, in particular its biological diversity and stability? How are we handling this critical element of Earth’s sustainability?