Scientists believe life appeared on Earth almost four-billion years ago, about half a billion years after our relatively young planet formed. It would be fascinating to see how life arose and managed to hang on.
If scientists were to invent time travel to take us back through Earth's history, we'd see little life for most of the four-billion years. Plenty was happening but at a microscopic level as organisms worked out all the intricacies of survival: finding food and energy, evading predators, fighting off disease (even bacteria get virus infections), reproducing and eliminating waste.
Subscribe to Science Matters
Once those fundamental details were worked out, more complex cells arose by incorporating other cells within themselves to perform specialized functions like capturing energy from the sun (photosynthesis) or generating energy from stored molecules. The stage was set for the final blossoming of life into forms visible to creatures like us: multicellularity. Once an organism was made up of many cells, a division of labour was possible. Various cells specialized in movement, eating, digestion, excretion and reproduction. All of this occurred in the last fifth of life's existence as seas and land filled with wondrous animals and plants.
It's a magnificent story and we only know the barest outlines. We tend to focus on big life forms like trees, elephants and whales. That's understandable. They're often spectacular. But our bias toward the big and impressive overlooks the importance, and beauty, of what are often dismissed as "creepy crawlies", such as worms, insects, fungi and bacteria.
I was an avid bug collector as a boy. To me, insects were endlessly riveting. Many of them display spectacular colours and patterns and occur in shapes and forms that are far more bizarre and surprising than any Hollywood sci-fi creation. My childhood fascination evolved in college to a focus on heredity in an insect, a common fruit fly, which has revealed so much about genetic principles in humans.
In our concern with protecting grizzlies and polar bears, whooping cranes and redwood trees, wolves and caribou, we give short shrift to the small creatures that keep the planet livable. Tiny organisms and plant roots filter water as it percolates through soil; insects, bacteria and fungi help plants, animals and dung decompose to create soil; bacteria in legumes capture atmospheric nitrogen and fix it in soil; all green things exchange carbon dioxide for oxygen as they capture sunlight that animals like us can consume and store for our own use. In fact, bacteria directly produce up to half the oxygen we breathe. Microbes in the human body outnumber cells by 10 to one, and many of them keep us alive by helping us digest food and combat infection, among other services.
Years ago, scientists in Norway showed that a single teaspoon of soil from a beach contained more than 4,000 different species of bacteria. Another teaspoon taken from a nearby deciduous forest yielded a similar number of species, most of them different from the beach group. Soil is not dirt or inert material; it is a complex community of living organisms, yet modern farming techniques often wipe them out.
Scientists estimate that for every human, there are 200-million insects on Earth. They are important parts of ecosystems, providing services such as pollination, food and pest control. Of all insect species, very few are harmful to humans, yet we spray powerful chemicals that kill all insects just to get at the tiny fraction that causes problems for us.
Because all life forms have evolved ways to find food, avoid being eaten, heal from infection, reproduce and eliminate waste, we have much to learn if we show some respect and patience to see how they create solutions. Scientists discovered penicillin as a fungus's way of warding off bacteria. They found cancer-fighting vincristine in the rosy periwinkle and taxol in yew trees. Restriction enzymes, vital tools of genetic engineers, are used by bacteria to fight viral infection.
We focus on charismatic species like whales, pandas, cedar trees and seals as poster children for conservation. But the small things that keep the biosphere going for creatures like us are probably more threatened because we ignore them. If we spend time studying them, they have much to teach us.