Living back in the seventeenth century, you might have had a hobby of searching the ground for Tongue Stones or Devil’s Toenails or Snake’s Heads. These were curious objects and certain daft gents would pay good money to add these “formed stones” to their collections.
Formed Stones is another of those quaint terms lost in the dusty corners of history. Today we call them fossils. [Not to leave you hanging, Tongue Stones were fossilized shark’s teeth, Snake’s Heads were ammonites, and Devil’s Toenails the curled shells of a bivalve called Gryphaea.]
Once upon a time they were the subject of intense and bitter debates. What, exactly, were these strange things? A few fringe types maintained that they were the remains of animals somehow turned into rocks. The majority held that they were simply naturally shaped rocks that happened to resemble living things.
“Happened to?” Well, not exactly. It was widely thought that they were demonstrations of the power of Platonic Forms. For Plato, Forms were the perfect patterns of Things. We recognize that a dog is a dog not because it looks like a dog but because it reflects the characteristics of the ideal Form of Dogness. (I always thought this was close to the silliest idea in all philosophy …which is going some.) Just as plants and animals naturally conformed to the shapes of ideal Platonic models, the sheer power of those perfect Forms caused even inert minerals to imitate them.
Eventually, naturalists came to accept that they were, in truth, the actual remains of plants and animals. This acceptance would have come sooner if so many fossils hadn’t been unlike any known organisms. The recent voyages of Cook and others made it hard to pretend that the fossils were the remains of beings still living in some unknown part of the world. To accept the idea that a great number of these fossils looked like nothing alive meant that one or both of two horrible ideas must be true: Either some species had become extinct or else some had been so transformed that they no longer resembled their ancestors.
The problem with both ideas was the Bible. Everyone knew that God had created all the flora and fauna in the seven days of creation. Each was perfectly suited to its place in Creation. Therefore for a species to die out or be transformed was impossible as either would mean it had been created somehow imperfect, which was blasphemy. And either would leave behind an empty niche in God’s Magnum Opus, which was equally blasphemous.
More data were needed. By the beginning of the nineteenth century, those thousands of fossils had grown to millions. Geologists had also noticed that there was a consistent pattern to the rock layers of the earth and that many layers could be identified by the mixture of fossils they contained. Ultimately, by using the simple idea that the upper layers of rock had been deposited on existing and therefore older layers, a relative time scale was built.
It wasn’t long before a couple of disturbing facts became apparent. First, it was confirmed that the further away in time one got from the present, the less the fossils resembled living plants and animals and more of them were simply not represented by living organisms. Second, it was apparent that the amount of time required to lay down all those layers was one whole heck of a lot longer than the roughly six thousand years the Bible seemed to allow. By the time the eighteenth century was drawing to a close, two uncomfortable questions had moved to the forefront of the discussion: how old is the earth and how do its new species arise?
The geologists suggested the answer to the first question might be measured in millions, or even hundreds of millions of years. That made the answer to the second both easier and harder. Easier, because millions of years offered a pretty broad span for new speciation to occur. Harder, because if millions of species had flourished for hundreds of millions of years, then the fossils that they had found to date could not represent even a fraction. It was as if someone were asked to write a history of a country but were only allowed to drop by once a century and take a single photograph to capture its status.
Given the imperfect record, theories abounded. Accepting that extinctions occurred, how could new species arise? Had God kept right on creating new ones to replace the old? And why did new ones both resemble and differ from older, extinct versions? Étienne Geoffroy St. Hilaire, a solid Platonist (here we go again), argued that there existed “archetypes” for species. All vertebrates, he said, are only modifications of a single archetype, a single Form that shapes all of them. Inherently, all new species will conform to similar patterns as the old, since they share archetypes. His opponent, Georges Cuvier, maintained that all species are shaped by what they do. The apes and men both have hands because they both grasp things. Inherently, then, all new species with the same functions will share features.
Jean-Baptiste Lamarck, disagreeing with both, rejected extinction altogether. He also rejected the idea of any fixed model for a species. Instead, he believed that organisms were modified by environment. That is, each individual’s experiences changed him and such changes could be passed to his descendants. Transmutation (what we would call evolution), therefore, could occur with great rapidity. Given the incomplete nature of the fossil record, what appeared to be the disappearance and replacement of species were really snapshots of changing species with huge gaps between photos.
Up until 1859, that established the sides of the debate: There were extinctions, but God created new species to replace the old. They were similar because they a) conformed to the same archetype, or b) they had the same functions, so shared the same shapes. No, there were no such things as extinctions (and therefore no newly created species), there were just a lot of organisms changing rapidly to adjust to changing circumstances.
Finally, in November of 1859, along came Charles Darwin’s Origin of Species. Here there were no Forms and no special creations of new species. He suggested that the changing conditions of the earth provided an endemic struggle for survival for all species. Those that couldn’t adapt, died out. Of those who could, those best adapted would be the most successful. With enough time and enough modifications, those best suited would become new species.
There is no question that Darwin won that fight. In today’s science there are no Forms, no magical templates to guide evolution.
None of these debating gentlemen had any idea that underlying earthborn life was a single molecule called DNA. The solutions the various species could try in order to meet environmental challenges were limited by their DNA. In the next ice age, none of us is going to try a third arm or leg or eye: DNA makes us all bilaterally symmetrical. For that matter, given all of the wild and wonderful shapes that mammals have adopted to cope with our unstable planet, the basic plan is surprisingly inflexible. Next time you visit the Natural History Museum, notice how almost all of the warm bloods have five digits on the forelimbs, the same number of bones in those forelimbs, the same type of hip bones, the same number of bones in their hind limbs, etc., etc.
Hmmm. Sounds a lot like we are all constrained to follow a Form called DNA, doesn’t it?