Telling the Evolutionary Time: Molecular Clocks and the Fossil Record

Figure 1.3

Global rates of amino acid replacement for GPDH, G6PD, PGD, SOD,

TPI, and XDH. The time unit (abscissa) is 100 million years.

The rates

on the right are for replacements

×^10

−^10

per site per year. These rates correspond to comparisons between

Drosophila

subgenera, mammal orders, or fungi

(rows 3, 5, and 7 in

Table 1.3

). The comparisons between

Drosophila

subgenera and mammal orders correspond to roughly contemporary tim

e lapses (60

Ma and 70 Ma, respectively). Other points in the figure are for other comp

arisons, such as between kingdoms (1100 Ma) or animal

phyla (600 Ma; see also

Table 1.3). For SOD the rate of 5 on the right is

for comparisons between species within the

melanogaster

and

obscura

groups (see also

Figure 1.2

).

MOLECULAR CLOCKS: WHENCE AND WHITHER? 17