Evolution__3rd_Edition

450 PART 4 / Evolution and Diversity
Divergence (%)
40
30
20
10
changes at the same site become common the phylogenetic information in the
sequence similarity is lost a a stopwatch with only a seconds hand would be no use in
comparing professors’ lecture times. Likewise, slowly evolving molecules are useless
for fine phylogenetic resolution because they will not have changed enough.
(a) Mitochondrial ribosomal RNA gene (b) Nuclear ribosomal RNA gene
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0 100 200 300 400 500 600 700
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0 200 400 600 800 1,000
Time (Myr)
Time (Myr)
(c) Cetaceans (d) Major animal groups
Porpoises
Dolphins
Sperm
whales
Baleen
whales
Beaked
whales
Other
mammals
Figure 15.16
Matching the molecule to the phylogenetic problem. The
ribosomal RNA genes in the mitochondria (a) evolve more
rapidly than those in the nucleus (b). The different points are
for species pairs, for which the date of their common ancestor
can be estimated from fossils. The graphs tail off (at about 33%
divergence) because of multiple substitutions at a site.
Divergence (%)
80
60
40
20
Odontoceti
Mysticeti
Odontoceti
Coelenterates (2)
Chordates (4)
Echinoderms (4)
Insects
Millipede
Chelicerate
Crustaceans (3)
Oligochaete annelid
Polychaete annelid
Pogonophore
Brachiopod
Chiton
Nudibranch mollusk
Bivalve mollusks (2)
Sipunculid
(c) Phylogeny of dolphins and whales, using mitochondrial
rRNA genes; the deepest root is about 35 million years ago.
(d) Relations of major animal groups, as revealed by nuclear
rRNA genes; the deepest root is probably over 600 million
years ago. Redrawn, by permission of the publishers; (a and b)
from Mindell & Honeycutt (1990), (c) from Milinkovitch et al.
(1993), and (d) from Lake (1990).
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