Colorful Pebbles and Darwin's Dictum

Science is an exquisite blend of data and theory

In 1861, less than two years after the publication of Charles Darwin's On the Origin of Species, in a session before the British Association for the Advancement of Science a critic claimed that Darwin's book was too theoretical and that he should have just "put his facts before us and let them rest." In a letter to his friend Henry Fawcett, who was in attendance in his defense, Darwin explained the proper relationship between facts and theory:

About thirty years ago there was much talk that geologists ought only to observe and not theorize; and I well remember someone saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service!

There are few thinkers in Western history with more profound insights into nature than Charles Darwin, but for my money this is one of the deepest single statements ever made on the nature of science itself, particularly in the understated denouement. If scientific observations are to be of any use, they must be tested against a theory, hypothesis, or model. The facts never just speak for themselves, but must be interpreted through the colored lenses of ideas — percepts need concepts.

When Louis and Mary Leakey went to Africa in search of our hominid ancestors, they did so not based on any existing data, but on Darwin's theory of human descent and his argument that because we are so obviously closely related to the great apes, and the great apes live in Africa, it is here that the fossil remains of our forebears would most likely be found. In other words, the Leakeys went to Africa because of a concept, not a percept. The data followed and confirmed this theory, the very opposite of the way we usually think of science working.

If there is to be an underlying theme in this column — a substrate beneath the surface topography (to continue the geological metaphor) — it is that science is an exquisite blend of data and theory, facts and hypotheses, observations and views. If we think of science as a fluid and dynamic way of thinking instead of a staid and dogmatic body of knowledge, it is clear that the data/theory stratum runs throughout the archaeology of human knowledge and is an inexorable part of the scientific process. We can no more expunge ourselves of biases and preferences than we can find a truly objective Archimedean point — a God's eye view — of the human condition. We are, after all, humans, not gods.

In the first half of the twentieth century philosophers and historians of science (mostly professional scientists doing philosophy and history on the sid