MOUSE – SPRING 2011
No one really knows how many species there are. No one has even
really collected the numbers already named, but there are probably ~1.5 million already named.
If you include the those we are pretty sure are “out there” but which we have not yet named,
perhaps not yet even seen, there may be as many as 3-5 million. Some people think 30 M.
By the early 1700s, several classification systems had cropped up, all cumbersome. In 1735,
Linnaeus published his
. Linnaeus introduced binomial nomenclature, in
Latin, of course, indicating the Genus and species:
. It was an instant hit - basically wiped out the competition.
– Linnaeus also used a series of nested
, each more inclusive as one moved
up the ladder,
. As an
organizing scheme, it could not be beat; we’re still using it. Linnaeus did not understand why it
worked (in other than religious terms), but the fact is that it “felt right.”
It still does, today.
– A particular species, say
, is a taxon
. A particular genus, say
, is also
a taxon (a more inclusive taxon). We use the term
to mean “a unit”, the name for which
is secondary, but whose existence is definite. The plural of taxon is
. A particular family is
also a taxon, a higher (more inclusive) taxon, and so on.
The members within any given taxon were understood to be related, by which Linnaeus and his
contemporaries meant, “created on the same general plan by God”, small (or large) variations
on a single theme. Small variations for species within a genus, larger variations for genera
within a family, and so on, but all ordered in a convenient way that we had only to discover.
Of course, once the idea of evolution took hold, the meaning of
‘related’ and the relevance of categories changed forever. Darwin held that the close relationship
of different species in the same genus was due to their recent descent from a common ancestor.
Genera were more different, because that common ancestor was further back in time.
– He viewed all organisms as having sprung from a vast
tree of life
idea of a tree had real appeal, because people could visualize a tree, and could understand how
it grew. Darwin plays the tree theme to the hilt. He added the important realization that
Linnaean classification represented the actual historical (evolutionary) record.
Cladogenesis vs Anagenesis
– Darwin’s hypothesis had two major features,
splitting of one lineage into two or more descendent lines), and
change of various characters within each of the descendents). The idea of post-Darwinian
systematics is to place all taxa within higher taxa that are internally