Descent with Modification A Darwinian View of Life

Page
4

mainly on juvenile

guppies (which do not

express the color genes)

Guppies: Adult males have

brighter colors than those

in “pike-cichlid pools”

Experimental

transplant of

guppies

Pools with

killifish,

but no

guppies prior

to transplant

Predator: Pike-cichlid; preys mainly on adult guppies

Guppies: Adult males are more drab in color

than those in “killifish pools”

Source

population

Transplanted

population

Source

population

Transplanted

population

Number of

colored spots

Area of colored

spots (mm2)

12

12

10

10

8

8

6

6

4

4

2

2

0

0

RESULTS

EXPERIMENT

Slide 23

Experiment in Natural Selection Results

Endler transferred brightly colored guppies (with few predators) to a pool with many predators. As predicted, over time the population became less brightly colored.

Endler also transferred drab colored guppies (with many predators) to a pool with few predators. As predicted, over time the population became more brightly colored.

Slide 24

Directional Natural Selection: The Evolution of Drug-Resistant HIV

The use of drugs to combat HIV selects for viruses resistant to these drugs.

HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome.

The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus.

Some individual HIV viruses have a variation that allows them to produce DNA without errors. These viruses have greater reproductive success.

The population of HIV viruses has therefore developed resistance to 3TC.

Slide 25

The ability of bacteria and viruses to evolve rapidly poses a challenge to our society.

Natural selection does not create new traits, but edits or selects for traits already present in the population.

The local environment determines which traits will be selected for or selected against in any specific population.

Slide 26

Fossil Evidence of Change Over Time

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, San

Bernardino County, California

Depth (meters)

0

2

4

6

8

10

12

14

16

18

1

2

3

3

3

1

2

4

4

Slide 27

Paleontologists study fossils of possible transitional forms: Whale Ancestors

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)