Series - "Icons of Evolution, Darwin's Tree of Life"

Last week we looked at the first "Icon of Evolution", the Miller-Urey Experiment. In this post we will be looking at the second "Icon of Evolution, Darwin's Tree of Life". This topic will be broken up into 4 parts, Darwin's Tree of LifeDarwin and the fossil RecordMolecular Phylogeny and why this is not scientific.

Darwin's Tree of Life


"This was the process Darwin illustrated in The Origin of Species. The vertical dimension in Darwin's drawing represents time, with oldest at the bottom and newest at the top, while the horizontal dimension represents differences among organisms. Darwin believed that minor variations within the original ancestral species were gradually amplified over the course of many generations into larger differences that separated species from one another. As he put it, "the small differences distinguishing varieties of the same species, steadily tend to increase, till they equal the greater differences between species" 

Taking each horizontal line in his illustration to indicate a thousand generations, Darwin estimated that "six new species, marked by the letters n14 to z14" at the top, might have been produced after fourteen thousand generations. In fact, since "the original species (I) differed largely from (A), standing nearly at the extreme end of the original genus" at the bottom, it seemed probable that "the six new species descended from (I), and the eight descendants from (A), will have to be ranked as very distinct genera, or even as distinct sub-families." Still greater differences could be explained on a larger time scale. For example, if one were to take "each horizontal line [to] represent a million or more generations," Darwin saw "no reason to limit the process of modification, as now explained, to the formation of genera alone," but considered it equally capable of producing "new families, or orders,... [or] classes."

Thus the large differences separating orders and classes would emerge only after a very long history of small differences: "As natural selection acts solely by accumulating slight, successive, favorable variations, it can produce no great or sudden modifications; it can act only by short and slow steps." These "short and slow steps" give Darwin's illustration its characteristic branching-tree pattern. Therefore, if the bottom line in Darwin's diagram represents varieties, the top line might be different species or genera. If we take those genera, put them at the bottom, and start the process over, we might get families or orders; then if we put those orders at the bottom and repeat the process, we might get classes or even phyla. But in Darwin's theory, there is no way phylum-level differences could have appeared right at the start. Yet that is what the fossil record shows."

Jonathan Wells. Icons of Evolution: Science or Myth? Why Much of What We Teach About Evolution Is Wrong 

Next week we will be looking at Darwin and the fossil record.

Remember..... Have an Intelligent Faith!!