Torch, Fall/Winter 2009

Fall–Winter 2009 | TORCH 5 The Uncertainties of Theory When Darwin published Origin , the science of geology and paleontology was still in its infancy. So, he drew upon contemporary examples of “evolution” to support his theory. For example, he cited his domestic pigeon breeding experiments as evidence that generational change occurs within a particular group of species. He reasoned that in natural settings some offspring have physical traits that are better suited for survival than their siblings. The better-suited offspring survive, while the inferior offspring die and, therefore, fail to reproduce. In the 1859 edition of Origin , Darwin included a figure of an evolutionary tree (Figure 1). It shows that, over time, similar offspring diverge and become more and more dissimilar from one another. Eventually, what began as members of the same species become different species. Darwin then reasoned that all the species in the world today might have arisen from just a few primordial organisms. He realized the fossil record didn’t quite bear out this evolutionary story. In fact, he acknowledged the fossil record was fairly incomplete but believed future discoveries would help support his theory. As he explained in his book, Darwin recognized the following major problems with the fossil record: Problem #1: Vast numbers of missing intermediate species “If my theory be true, numberless intermediate varieties, linking most closely all the species of the same group together, must assuredly have existed. … evidence of their former existence could be found only amongst fossil remains, which are preserved … , in an extremely imperfect and intermittent record. …Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory ” (pp. 179, 280). Darwin recognized that his theory demanded vast numbers of intermediate species, from lower to higher groups. Those species were missing in his day and are still missing. A few purported intermediates have been found, but the numbers are far from what they should be if his theory is true. Problem #2: Sudden appearance of multiple species within the same layers “There is another and allied difficulty, which is much graver. I allude to the manner in which numbers of species of the same group suddenly appear in the lowest known fossiliferous rocks. Most of the arguments which have convinced me that all the existing species of the same group have descended from one JESSE KARJALAINEN / ISTOCKPHOTO Figure 1: Darwin’s only figure from the first edition of On the Origin of Species (1859). This evolutionary tree appears in Chapter 4, which introduces his theory of natural selection. Species A diverges into many separate species by the time it reaches the top of the figure, after tens of thousands of generations.