148 Evolution and the Fossil Record
chapter 14). But for the many successes of molecular biologists, there have been some embar-
rassments. One study (Graur et al. 1991) concluded that guinea pigs were not rodents! This
was quickly shot down by numerous other molecular labs (e.g., Cao et al. 1994) that showed
the flaws in the analysis. No method in science is perfect, but molecular methods have
proven very powerful, and there are so many checks and balances in the peer-review process
that if one lab makes a mistake, other labs correct it. But if many labs get the same results
from different molecules, then that is probably good evidence that they are onto something.
The Branching Tree of Life
From the most remote period in the history of the world organic beings have been
found to resemble each other in descending degrees, so that they can be classed in
groups under groups. This classification is not arbitrary like the grouping of the stars
in constellations. The existence of groups would have been of simpler significance, if
one group had been exclusively fitted to inhabit the land and another the water; one
to feed on flesh, another on vegetable matter, and so on; but the case is widely differ-
ent, for it is notorious how commonly members of even the same subgroup have dif-
ferent habits. . . . Naturalists, as we have seen, try to arrange the species, genera, and
families in each class, on what is called the Natural System. But what is meant by this
system? Some authors look at it merely as a scheme for arranging together those liv-
ing objects which are most alike, and for separating those which are most unlike. . . .
But many naturalists think that something more is meant by the Natural System; they
believe that it reveals the plan of the Creator; but unless it be specified whether order
in time or space, or both, or what else is meant by the plan of the Creator, it seems
to me that nothing is thus added to our knowledge. . . . I believe that this is the case,
and that community of descent—the one known cause of close similarity in organic
beings—is the bond, which though observed by various degrees of modification, is
partially revealed to us by our classifications.
—Charles Darwin, On the Origin of SpeciesAs this discussion of systematics has shown, there are many different methods for decipher-
ing the history of life. From comparison of their external and internal anatomical features, to
the similarities in embryonic history, to the details of the molecules in every cell, the branch-
ing history of life is revealed in nearly every aspect of organisms. The fact that so many
systems give the same answer makes it very robust. If we can’t resolve the phylogeny from
the anatomy, perhaps the molecules will help out. If the fossil record is poor in one particular
group, we look to other sources of data. But if the fossil record or anatomical data is excel-
lent, we are cautious about molecular conclusions that differ widely from our paleontologi-
cal estimates. Thus, although no one method is perfect all the time, each method has its own
strengths and weaknesses that allow us to decipher the problem, one way or another.
In addition, the advent of rigorous testable methods of phylogenetic reconstruction
through cladistic analysis of anatomical details and of molecular sequences has made our
efforts at determining the true history of life more successful than ever before. When I was
a graduate student, many areas of evolutionary history were controversial and poorly
resolved, based on the evidence that was available in the 1970s. But one after another, the