Evolution Among Lineages
The Pattern of Macroevolution
Evolution is not progress. The popular notion that evolution can be represented as a series of
improvements from simple cells, through more complex life forms, to humans (the pinnacle of
evolution), can be traced to the concept of the scale of nature. This view is incorrect.
All species have descended from a common ancestor. As time went on, different lineages of
organisms were modified with descent to adapt to their environments. Thus, evolution is best
viewed as a branching tree or bush, with the tips of each branch representing currently living
species. No living organisms today are our ancestors. Every living species is as fully modern as
we are with its own unique evolutionary history. No extant species are "lower life forms,"
atavistic stepping stones paving the road to humanity.
A related, and common, fallacy about evolution is that humans evolved from some living species
of ape. This is not the case -- humans and apes share a common ancestor. Both humans and
living apes are fully modern species; the ancestor we evolved from was an ape, but it is now
extinct and was not the same as present day apes (or humans for that matter). If it were not for
the vanity of human beings, we would be classified as an ape. Our closest relatives are,
collectively, the chimpanzee and the pygmy chimp. Our next nearest relative is the gorilla.
Evidence for Common Descent and Macroevolution
Microevolution can be studied directly. Macroevolution cannot. Macroevolution is studied by
examining patterns in biological populations and groups of related organisms and inferring
process from pattern. Given the observation of microevolution and the knowledge that the earth
is billions of years old -- macroevolution could be postulated. But this extrapolation, in and of
itself, does not provide a compelling explanation of the patterns of biological diversity we see
today. Evidence for macroevolution, or common ancestry and modification with descent, comes
from several other fields of study. These include: comparative biochemical and genetic studies,
comparative developmental biology, patterns of biogeography, comparative morphology and
anatomy and the fossil record.
Closely related species (as determined by morphologists) have similar gene sequences. Overall
sequence similarity is not the whole story, however. The pattern of differences we see in closely
related genomes is worth examining.
All living organisms use DNA as their genetic material, although some viruses use RNA. DNA is
composed of strings of nucleotides. There are four different kinds of nucleotides: adenine (A),
guanine (G), cytosine (C) and thymine (T). Genes are sequences of nucleotides that code for
proteins. Within a gene, each block of three nucleotides is called a codon. Each codon designates
an amino acid (the subunits of proteins).
The three letter code is the same for all organisms (with a few exceptions). There are 64 codons,