Evolution__3rd_Edition

460 PART 4 / Evolution and Diversity
Figure 15.23
Paralog rooting. (a) A gene
duplicates into two copies, at
different loci. The species then
evolves into four descendants,
each with copies of the two
genes. (b) We use the molecular
sequences of the eight genes to
infer the unrooted gene tree. It
has been drawn to show the
logic of the method, with two
sets of four genes arranged
as mirror images. A more
conventional tree would have
the eight genes written down
the page. Given this tree, we
infer that the root is in the
long branch connecting the
two mirror-image subtrees.
(c) Thus, if we have the
unrooted species tree, we can
use the pattern in (b) to infer
where the root is. The answer
is correct: it matches the real
pattern of evolution in (a).
The fossil ape Ramapithecus ...
(a) Pattern of evolution
a b
Duplicated genes
Species 1 2 3 4
(b) Gene tree
(c) Species tree
a1 b 1
a2 b 2
a3 b 3
a4
b 4
Location of root
1 3
2 4
15.13 Molecular evidence successfully challenged
paleontological evidence in the analysis of human
phylogenetic relations
a1
a2
a3
a4
It is always interesting when two independent lines of evidence, from very different
fields, are applied to the same question. This sections looks at a conflict between fossil
and molecular evidence concerning the time of origin of the human evolutionary
lineage.
“Ramapithecus” (which is now classified in the genus Sivapithecus) is a group of
fossil apes that lived about 9–12 million years ago. Until the late 1960s, almost all
b 1
b 2
b 3
b 4
..