Evolution__3rd_Edition

56 PART 1 / Introduction
Figure 3.6
All modern tetrapods have a
basic pentadactyl (five digit)
limb structure. The forelimbs of
a bird, human, whale, and bat
are all constructed from the
same bones even though they
perform different functions.
Adapted with permission from
Strickberger (1990). © 1990
Boston: Jones & Bartlett
Publishers.
Humerus
Ulna
Frog Lizard Bird
Radius
Carpal 1
Ulna
Carpal
5
2
3
4
Humerus
Ulna Ulna
Radius
Carpal
5
4 3
Humerus
Carpal
Human Cat Whale Bat
Humerus
5
4
Humerus
Ulna
Radius
3
2
1
Carpal
Radius
5
2
Ulna
1
Carpal
1
2
3
4
5
4 1
3
2
Radius
Humerus Humerus
Radius
5
Ulna Radius
4
Carpal
What could be more curious than that the hand of man formed for grasping, that of a
mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should
all be constructed on the same pattern and should include similar bones and in the same
relative positions?
The pentadactyl limb is a homology in the pre-Darwinian sense: it is a similarity
between species that is not functionally necessary. Pre-Darwinian morphologists
3
3
2
1
2
1
..