Evolution  (Page 2/9)

You are probably familiar with some of these explanations. Many ancient peoples imagined that the world was created in the form that exists now, and that blue whales, pythons, and lilac bushes were created and unchanged since that creation. This is known as typology ; every species conforms to an ideal and unchanging type, and all members of the species are true to that type. Wolves are a type, and all wolves (within certain parameters) were considered to be similar to all other wolves, but not similar to foxes, and even less similar to lions. And all of these creatures had ancestors who were also true to the type. Once it became clear that there had been creatures, preserved in the fossil record, unlike any creatures seen today, other explanations were needed to account for these new observations. When it became clear, from geology, that the earth was very ancient, and had been in existence for millions and even billions of years, other explanations became even more satisfactory. When it became clear, from studies of comparative anatomy, that many creatures shared anatomical and developmental similarities, even though they were of different types, other explanations became obvious.

We won’t go through the many explanations for the diversity of life that have been proposed and been discarded over the centuries. There are lots of places where you can read about that historical progression, and it is interesting, for sure. Rather we will get to the explanation that is the most widely accepted scientific explanation today, and show how this explanation is supported by evidence, and also leads to predictive hypotheses that can serve as a further test of the explanation. That explanation is known as the Theory of Evolution.

As discussed in the previous chapter, theories are powerful frameworks for explaining observations, and for making new predictions about the natural world. The theory of evolution is no exception. In fact, it is the most powerful explanatory framework in biology today. Theodosius Dobzhansky, a famous biologist, expressed this sentiment quite well when he wrote in 1973, “Nothing in biology makes sense except in the light of evolution.” On a daily basis, scientists around the world are using the theory of evolution to generate hypotheses, to interpret conclusions, and to make contributions to scientific knowledge. So let’s look at that powerful explanation in more detail.

At its simplest, evolution is defined as “descent with modification”. That is joined to another concept, natural selection, to give us the first expression of the theory of evolution, published by Charles Darwin in 1859. Darwin’s genius was in recognizing, and thoroughly explaining, that descent with modification was a common phenomenon, and that selection, whether natural or artificial (e.g. animal breeding) was an explanation for life’s diversity. So let’s look more closely at natural selection, since Darwin identified it as the engine that drives the process of evolution.