The Evolution of Evolution 113was Darwin’s evidence? Why does it demand an evolutionary explanation? How does cre-
ationism fail to explain it?
The Family Tree of Life
The first line of evidence had been emerging ever since the days of the Linnaean classi-
fication of animals in 1758, a full century before On the Origin of Species. The purpose of
Linnaeus’s classification scheme was to document God’s handiwork by discovering the
“natural system” of classification that God had used. Inadvertently, Linnaeus stumbled on
an obvious fact of nature: each group (such as a species) of animals and plants clusters with
other groups into larger groups (called taxa in the plural, taxon in the singular), such as a
genus or order, and those higher-level supergroups cluster into even larger groups (such as
classes or phyla) with additional taxa. For example, humans are part of a taxon (the family
Hominidae) that also includes chimps, gorillas, orangutans, and gibbons. The apes, in turn,
cluster together with the Old World monkeys (family Cercopithecidae) and New World
monkeys, lemurs, and bush babies into a larger group, the order Primates. The primates
are clustered with cows, horses, lions, bats, and whales in the class Mammalia. The mam-
mals are clumped with fishes, birds, reptiles, and amphibians in the subphylum Vertebrata.
Together with sponges, corals, mollusks, and other invertebrates, the vertebrates are part of
the kingdom Animalia. The natural system for arranging and classifying life is a hierarchi-
cal system of smaller groups clustered into larger groups, which is best represented as a
branching tree of life.
By Darwin’s time, this branching pattern of life was even more strongly supported and
led many people toward the notion that life had undergone a branching pattern of evolution
(although not as boldly as Darwin suggested it). All of this was deduced by comparison of
features visible to the naked eye or simple magnifier, primarily in the anatomy of the organ-
ism. But not even Darwin could have dreamed that the genetic code of every cell in your
body also shows the evidence of evolution. Whether you look at the genetic sequence of
mitochondrial DNA or nuclear DNA or cytochrome c or lens alpha crystallin or any other
biomolecule, the evidence is clear: the molecules show the same pattern of nested hierarchi-
cal similarity that the external anatomy reveals (fig. 4.7). Our molecules are most similar
to those of our close relatives, the great apes, and progressively less similar to those more
distantly related to us.
Teasing out the details of this molecular similarity shows us a simple fact: every molec-
ular system in every cell reveals the fact that life has evolved! If we were specially cre-
ated and unrelated to the apes, why would we share over 98 percent of our genome with
the chimpanzee and progressively less shared genome with primates who are less closely
related to us? If God created it to look that way, then we are back on the “deceptive God”
problem that faced Gosse’s Omphalos hypothesis. No, the simplest interpretation is that
the molecules tell the truth: life has a common origin and exhibits a branching pattern of
ancestry and descent.
Homology
As comparative anatomy became a science in the early 1800s, anatomists were struck by how
animals were constructed. Organisms with widely differing lifestyles and ecologies used the