"Well, it's easy to be wise after the event. Darwin figured the age of the earth to be 300 million years. Because one thing, at least, was clear: neither Lyell's theory of gradual geological evolution nor Darwin's own theory of evolution had any validity unless one reckoned with tremendously long periods of time."
"How old is the earth?"
"Today we know that the earth is 4.6 billion years old."
"Wow!"
"Up to now, we have looked at one of Darwin's arguments for biological evolution, namely, the stratified deposits of fossils in various layers of rock. Another argument was the geographic distribution of living species. This was where Darwin's scientific voyage could contribute new and extremely comprehensive data. He had seen with his own eyes that the individuals of a single species of animal within the same region could differ from each other in only the minutest detail. He made some very interesting observations on the Galapagos Islands, west of Ecuador, in particular."
"Tell me about them."
"The Galapagos Islands are a compact group of volcanic islands. There were therefore no great differences in the plant and animal life there. But Darwin was interested in the tiny differences. On all the islands, he came across giant tortoises that were slightly different from one island to another. Had God really created a separate race of tortoises for each and every island?"
"It's doubtful."
"Darwin's observations of bird life on the Galapagos were even more striking. The Galapagos finches were clearly varied from island to island, especially as regards the shape of the beak. Darwin demonstrated that these variations were closely linked to the way the finches found their food on the different islands. The ground finches with steeply profiled beaks lived on pine cone seeds, the little warbler finches lived on insects, and the tree finches lived on termites extracted from bark and branches ... Each and every one of the species had a beak that was perfectly adapted to its own food intake. Could all these finches be descended from one and the same species? And had the finches adapted to their surroundings on the different islands over the ages in such a way that new species of finches evolved?"
"That was the conclusion he came to, wasn't it?"
"Yes. Maybe that was where Darwin became a 'Darwinist'--on the Galapagos Islands. He also observed that the fauna there bore a strong resemblance to many of the species he had seen in South America. Had God once and for all really created all these animals slightly different from each other--or had an evolution taken place? Increasingly, he began to doubt that all species were immutable. But he still had no viable explanation as to how such an evolution had occurred. But there was one more factor to indicate that all the animals on earth might be related."
"And what was that?"
"The development of the embryo in mammals. If you compare the embryos of dogs, bats, rabbits, and humans at an early stage, they look so alike that it is hard to tell the difference. You cannot distinguish a human embryo from a rabbit embryo until a very late stage. Shouldn't this indicate that we are distant relatives?"
"But he had still no explanation of how evolution happened?"
"He pondered constantly on [yell's theory of the minute changes that could have great effect over a long period of time. But he could find no explanation that would apply as a general principle. He was familiar with the theory of the French zoologist Lamarck, who had shown that the different species had developed the characteristics they needed. Giraffes, for example, had developed long necks because for generations they had reached up for leaves in the trees. Lamarck believed that the characteristics each individual acquires through his own efforts are passed on to the next generation. But this theory of the heredity of 'acquired characteristics' was rejected by Darwin because Lamarck had no proof of his bold claims. However, Darwin was beginning to pursue another, much more obvious line of thought. You could almost say that the actual mechanism behind the evolution of species was right in front of his very nose."
"So what was it?"