Systematics and Evolution 137The first such unorthodox attempt of the 1950s and 1960s to reform the subjectivity and
fuzzy methodology of the old systematics was known as numerical taxonomy, or phenetics.
Its proponents tried to turn taxonomy into something that could be measured and coded into
a computer program, and then “objective” results would emerge. Although this movement
made some progress and pointed out many problems with the older system, eventually it
failed because some of its assumptions were faulty and unworkable. In addition, it turned
out that phenetics was not as objective as originally claimed. Subjectivity is still involved
when scientists measure and record data and decide which characters to use and even when
they run different computer programs on the same data. Numerical taxonomy ultimately
lost steam as a movement when it turned out that the same computer program might give
different answers for the same data, which made the entire objectivity advantage disappear.
But in the late 1960s, another systematic philosophy emerged to challenge the main-
stream orthodoxy. Known as phylogenetic systematics, or cladistics, it was originally pro-
posed by German entomologist Willi Hennig in 1950, but not widely followed until his
German text was translated into English in 1966. Unlike the phenetic movement, which
fizzled out soon after it was proposed, cladistics challenged the orthodoxy and eventually
became mainstream itself, primarily because of its clear and rigorous methods and also
because it worked to solve many previously insoluble problems. But in the 1960s and 1970s,
the introduction of cladistics met with much resistance and controversy, as the more outra-
geous ideas proposed were rejected by older scientists who could not imagine changing the
concepts that they learned as students. By the late 1980s, however, cladistic methods pre-
vailed in the systematics of nearly every group of organisms.
I was fortunate to witness most of the stages of this revolution in systematics. I began
as a graduate student at the American Museum of Natural History in New York in 1976,
just as the cladistic revolution was in full swing, so I got to see all the major debates and got
to know the key players. At the time, only the American Museum and a few other places
accepted these ideas; the rest of the country looked at the “New York cladists” in horror as
if we had a contagious disease. I gave my first professional talk at the Society of Vertebrate
Paleontology meeting in 1978 on cladistics of Jurassic mammals, and I was one of the few
people to mention cladistics at the entire meeting. Less than a decade later, all of the system-
atic talks at this same meeting were entirely cladistic, and those who stubbornly tried to do
things the old way struck us young Turks as musty old dogs who couldn’t learn new tricks.
New and outrageous ideas and challenges to the orthodoxy are always being proposed
in science, but most unorthodox ideas don’t go very far. It’s not because science is inher-
ently reactionary or conservative. On the contrary, there are always incentives for ambitious
young scientists to make a name for themselves by challenging orthodoxy. But all new ideas
must meet the test of peer review and scientific scrutiny and survive in the furnace of trial
and error. Most such ideas fail because their limitations eventually become apparent. Cladis-
tics became mainstream because it cleared up a lot of clutter in thinking and in practice and
because it works.
What is cladistics, and why is it different from the older methods of classification?
Hennig’s main insight was that the anatomical features, or characters, that we use to name and
describe organisms, are not all the same. Every organism is a mosaic of advanced (or derived)
features inherited from a very recent common ancestor and primitive features inherited from
distant ancestors. For example, we humans have advanced features such as our large brain
and bipedal posture, but we inherited our absence of tails from our ape ancestors (all apes