Taken largely from the Talk.Origins Archive web site, and is
used here with the kind permission of its author, According to
the theory of evolution, the "descent with modification" road to
humans (or any other group, for that matter) is paved with a
sequence of transitional fossils, spaced out in a time sequence
reflected in the ages of the fossils found. Since fossils of
soft-bodied animals are relatively rare (they don't fossilize
easily), the record is rather spotty prior to the first
appearance of vertebrates (in the form of jawless fishes), so
this lesson will focus only on the fossil record of vertebrates
As we study the growing number of fossils, we find that they
usually fit nicely into one group or another, and most of those
groups clearly show gradual change over time, even phasing into
new and different groups along the way, adding changes upon
changes. Nevertheless, many of those earlier groups apparently
had populations which continued to exist with very little
change, producing the modern day re