Page 130 - Introduction to Paleobiology and The Fossil Record

MACROEVOLUTION AND THE TREE OF LIFE 117

a 14 q 14 p 14 b 14 f 14 o 14 e 14 m 14 F 14 n 14 r 14 w 14 y 14 v 14 x XIV
14
XIII
XII
XI
a 10 f 10 m 10 E 10 F 10 w 10 z 10 X
a 9 f 9 m 9 w 9 z 9 IX
a 8 f 8 k 8 l 8 m 8 u 8 w 8 z 8 VIII
a 7 f 7 k 7 l 7 m 7 u 7 w 7 z 7 VII
a 6 f 6 k 6 m 6 u 6 z 6 VI
a 5 d 5 k 5 m 5 u 5 z 5 V
a 4 d 4 l 4 m 4 z 4 IV
a 3 l 3 m 3 t 3 z 3 III
a 2 s 3 m 2 t 2 z 2 II
a 1 m 1 z 1 I
A B C D E F G H I K L

(a) (b)
Figure 5.1 (a) Charles Darwin. (b) Branching diagram of phylogeny, the only illustration in On the
Origin of Species (1859). It shows how two species, A and I, branch and radiate through time. The
units I–XIV are time intervals of variable length, and the lower case letters (a, b, c) represent new
species.

Darwin laid the framework for evolutionary often represented as a branching tree diagram.
biology 150 years ago. Despite millions of Darwin’s idea was that life had diversifi ed to
essays, books and web sites discussing evolu- millions of species by the continued splitting
tion, no one has yet falsifi ed Darwin’s theory of species from a common stem (Fig. 5.1).
of evolution by natural selection, and so it Indeed, he proposed that all of life, modern
stands as the core of modern biology and and ancient, could be followed back down the
paleontology, just as Isaac Newton’s laws phylogenetic tree to a single point of origin:
stand at the heart of much of modern physics. modern evidence confi rms this remarkable
And yet, surprisingly, Darwin is quoted, and insight.
misquoted, by many special-interest groups Darwin’s branching diagram also explained
who want to use him in support of, or against, for the first time the meaning of the natural

their views of politics, sociology and religion. hierarchy of life that Linnaeus had discovered
So it is important to understand what Darwin 100 years earlier (Box 5.1). This natural inclu-
said, how his insights affect science today, and sive branching hierarchy is the basis of modern
how paleontology relies on modern evolution approaches to discovering the tree of life, the
as its basis. single great evolutionary tree that links all
Charles Darwin’s On the Origin of Species species living and extinct, from the modern
(1859) is usually remembered as the book biodiversity of over 10 million species, back
that made the case for natural selection as the to a single hypothetical species 3500 million
mechanism of evolution, sometimes called years ago in the Precambrian. Paleontological

“survival of the fittest” (see pp. 118–19). aspects of evolution, such as the tree of life
Since the time of Darwin, evolution has been and studies of processes over thousands and
seen in action in the laboratory and in the millions of years, are sometimes called mac-
field, and paleontologists use the principles of roevolution (“big evolution”) to distinguish

evolution to understand how species origi- them from microevolution (“small evolu-
nate. The origin of species is also core to a tion”), all the smaller-scale and shorter-term
second theme in Darwin’s writings, namely processes studied by biologists and geneticists
phylogeny, or the pattern of evolution that is in the laboratory or in the fi eld.