NOVA Online: Odyssey of Life (see bottom of page for navigation)
see bottom of page for navigation

How Did We Get Here?

Letter 1
Kenneth R. Miller, November 14, 1996

Dear Phillip,

I am always struck by the fact that human awareness of our place in nature, like so much of modern science, began with the industrial revolution. For much of history it was possible to believe that the great diversity of life on Earth was a fixed creation, that the living world had never changed. But when the first stirrings of industry demanded that fuel be dug from the earth and hillsides be leveled for roads and railways, the Earth's true past was dug up in abundance. In a few short decades museums filled with fossils that documented a living past dramatically different from the present- day.

This record of past life demanded explanation, and naturalists struggled to provide one. Georges Cuvier, the great naturalist of the Napoleonic era, adamantly maintained that species were fixed and unchangeable. His own studies of fossils, however, revealed a pattern of extinctions and appearances so compelling that even Cuvier had to propose a series of catastrophic extinctions and renewals in which new species appeared. Etienne Geoffrey, his contemporary, had a more direct explanation for the detailed sequences of fossil crocodiles that he studied. Geoffrey noted that as he went back in time, these fossils became less and less like those of contemporary animals. Geoffrey was not sure how it had happened, but the fossils left him with no doubt as to what had happened. Present-day crocodiles were the descendants of these ancient forms - crocodiles had evolved.

As you know, the fossil record includes not only the ancestors of crocodiles and whales, but also the ancestors of human beings. And this, of course, is why evolution remains controversial. The great achievement of Charles Darwin was that he was the first to propose a theoretical mechanism for the fact of evolution that is documented in the fossil record. The operation of that mechanism, natural selection acting over time upon the variation in species, is a demonstrable fact. However, this does not mean that we fully understand how new species are formed, that we can look to the fossil record and always say with certainty what forces were acting upon a particular species, or that we know enough to weigh the relative importance of natural variation, mutation, gene transfer, or geographic isolation in the process of evolution.

What is the current scientific status of evolutionary theory? Biology is far from understanding exactly how a single cell develops into a baby, but research suggests that human development can ultimately be explained in terms of biochemistry and molecular biology. Most scientists would make a similar statement about evolution. We cannot yet explain everything about our natural history, but we know enough to be sure that Darwin's mechanism was at the heart of it. How did we get here? We were produced by what Darwin called "descent with modification," a process of change that links us with the grand story of life on earth. In other words, like everything else on this warm and wonderful planet, we evolved.

(go to next letter)
(go to Debate contents)

Odyssey Home | How? | Morphing | Lens
Timing | Creepy Crawlies | Table of Contents

NOVA Home | WGBH Home | PBS Home
Search | Feedback | Shop
© 1996 WGBH