Accept nothing as truth unless you see it with your own eyes, cautioned Aristotle in the fourth century BC.
Fossils have been in the ground for millions of years and people have always been finding them. One need hardly labour the point that many fossils look like skeletons or impressions of life forms, no longer in existence, buried aeons ago. Why did it take thousands of years for people to accept such a simple explanation?
And that deeper fossils are more ancient than shallower fossils, suggesting life changed over time?
Well of course some people did realise that fossils revealed extinct life, but suffered ostracism, or far worse, for denying supernatural explanations. Charles Darwin's fame stems from his courage, in the face of entrenched resistance, in presenting more than a tree of life, but a reasoned mechanism for its slow change over time by means of natural selection.
Darwin understood well his debt to evolutionary thinkers of earlier centuries, of whom he acknowledged no fewer than 38 in the fourth edition of On the Origin of Species.
Rebecca Stott, a professor at the University of East Anglia and a Scholar at Cambridge University, explores how closely others came to pre-empting Darwin's ideas fully.
Whether Aristotle was on the right track more than 2000 years ago is at least worthy of close examination.
Since at least as early as the fourth century BC, philosophers have assembled life forms and fossils in patterns according to family likeness, but did anyone allude to natural selection itself before Darwin's 1859 publication?
Ninth-century Baghdad scholar Jahiz noted the web of life's connectivity, without evolutionary overtones. In the 15th century Leonardo da Vinci (inevitably) brought the experimental method to bear on the conundrum of shallow-water seashells found on mountain tops. Cockles could not have migrated the necessary distance in the duration of the Flood, he calculated, and were not carried by the deluge because they were attached to the rock. Simply, the mountain top was once an island protruding from a deep sea.
That did not amount to evolution, but supported a changing world. The powers of free thought and objective experimentation, however, are irrepressible. Abraham Trembley and his 18th-century contemporaries were enthralled by the ability of a hydra, a tiny aquatic creature, to regenerate from pieces, for thus its development was innate - another key advance.
The 1748 publication of the Telliamed was an epic in itself, its then-dead author's name de Maillet thinly concealed, his pivotal references to the transformation of life obscured, billions of years cautiously censored into thousands.
Such was the fear of speaking freely.
But momentum built in the 18th and 19th centuries as attitudes slowly changed with the growth of knowledge. In this superbly referenced study the author leads us colourfully and anecdotally through the contributions of the greater and lesser pre-Darwinians, including Charles' grandfather Erasmus, illuminating the twin themes of the stiff battle for freedom of expression and the principles of scientific reasoning.
However widely something is believed, if there's no evidence, it probably isn't so. Scientific answers are commonly simpler than the question.
• Clive Trotman lectures aboard cruise ships about science and scientists.
