Evolution, 4th Edition

EV oLUTioN iS ofTEN GRADUAL Darwin argued that evolution proceeds by

small successive changes (gradualism) rather than by large “leaps” (saltations).

How often phenotypes evolve by discrete rather than gradual change is debated.

Many higher taxa that diverged in the distant past (e.g., the animal phyla; many

orders of insects and of mammals) are very different and are not bridged by inter-

mediate forms, either among living species or in the fossil record. However, the

fossil record does document intermediates in the evolution of some higher taxa

(see Chapters 17 and 20). Gradations among living species are very common, as

we would expect if characters evolve gradually. For example, the length and shape

of the bill differ greatly among species of sandpipers, but the most extreme forms

are bridged by species with intermediate bills (FIGURE 2.19).

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_02.18.ai Date 11-02-2016 12-12-16

Q: When sourcing photos, would be nice to get photos on a white background. Label similar locations with red numbered dot if using it to compare

like structures (e.g, #1 shows frog teeth only on upper jaw while human has on both upper and lower, etc.).

If trying to identify “Advanced” features vs. “Primitive” features, we could use two dot colors and balloon text.

I have pulled screenshots from msp and roughly silhouetted for general layout if planning on using similar photos to the msp. These need replacing.

Until we get nal photos, I can’t take this very far.

FPO

human

skeleton

FPO

frog skeleton

(A) (B)

Derived features

include large cranial size

and single jaw bone

Derived features include

loss of teeth in lower jaw and

reduction of 5 to 4 ngers

Ancestral features include

short ribs, small cranium

and multiple bones in the

lower jaw (not visible).

Ancestral features include

FIGURE 2.18 Mosaic evolution. The skel- 5 ngers on the hand.

eton of a frog (A) shows ancestral (“primi-

tive”) characters such as short ribs, a small

cranium, and multiple bones in the lower

jaw (not visible in photo). In mammals such

as humans (B), the ribs connect to a breast

bone, the lower jaw has a single bone, and

the enlarged cranium houses a large brain—

derived characters. Characters that are more

derived in frogs than in humans include loss

of teeth in the lower jaw, reduction from

five to four fingers, fused tibia and fibula in

the hind leg, and fusion of tail bones into a

rod (urostyle).

FIGURE 2.19 Graded differences in bill length in these closely

related members of the sandpiper family suggest that evolution

has been gradual. (A) Upland sandpiper (Bartramia longicauda).

(B) Whimbrel (Numenius phaeopus). (C) Eurasian curlew (Numenius

arquata). (D) Long-billed curlew (Numenius americanus).

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_02.19.ai Date 11-02-2016

(A)

(D)

(B) (C)

02_EVOL4E_CH02.indd 46 3/23/17 8:59 AM