History of life on Earth

“We’re related to the grass”, our biology teacher once proclaimed in his South Tyrolean accent that was at the same time unmistakable and highly liable to impersonation. Our 14-year-old, hormone-clouded minds can perhaps be forgiven for not immediately fathoming the profound scientifi c truth behind this statement, but looking back now, it stuck as poignant way of encapsulating what is perhaps the single most amazing fact biology has taught us. Whatever we see moving and growing around us is a member of our extended family. The mighty eagle and the ugly slug, the sequoia, the grass and the green slime on the beach — all are our relatives. And also what we don’t see — the microbes on our skin and in our guts, the bacteria that can kill us and the fungi that provide antibiotics — it’s all in the family. They all run on DNA, RNA and protein. They all share similar genes. They all share a common ancestry billions of years ago. (A word of caution: every living thing — we know of. It is after all possible that there are entire domains of life that are as yet undiscovered. Just consider the Archaea — one of the two or three fundamental domains of life — which were only discovered less than a lifetime ago. And while Archaea are clearly related to the rest of life, other, completely cryptic foreign life forms may exist, or may have existed, forever buried beyond recognition.) Granted, astute observers of nature had long noted that humans share a number of features with other creatures, like apes or other mammals. They share fewer features with reptiles and fewer still with fi sh. From these nested similarities, a hierarchy of decreasing relatedness could be delineated that, since Darwin’s time, has been taken to refl ect the temporal order of divergence during Earth’s history. The lineages leading to closely related groups branched later than those leading to more distant relatives. But only in the age of molecular biology have we come to fully appreciate History of life on Earth