1. Descent With Modification
Chapter 22

2. Evolution
change over time in the genetic composition of a population

3. Figure 22.2 The historical context of Darwin’s life and ideas
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1750
1800
1850
1900
1795
Hutton proposes his theory of gradualism.
1798
Malthus publishes “Essay on the Principle of Population.”
1809
Lamarck publishes his hypothesis of evolution.
1830
Lyell publishes Principles of Geology.
Figure 22.2 The historical context of Darwin’s life and ideas
1831–1836
Darwin travels around the world on HMS Beagle.
1837
1837
Darwin begins his notebooks.
1844
Darwin writes essay on descent with modification.
1858
Wallace sends his hypothesis to Darwin.
1859
The Origin of Species is published.

4. Scala Naturae
The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae

6. Carolus Linnaeus interpreted organismal adaptations as evidence that each was fixed and perfectly suited to an unchanging environment
Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying and naming organisms

7. Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier
Cuvier advocated catastrophism, speculating that each boundary between strata represents a past sudden catastrophe

8. Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today
Hutton proposed the idea of gradualism – slow change over time in formation of geologic features
Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time – processes we see today (like erosion) are the mechanisms of past change
These ideas strongly influenced Darwin’s thinking (old Earth)

9. Younger stratum
with more recent
fossils
Older stratum
with older fossils

10. Lamarck (1744-1829) applied the concept of gradualism to
biological evolution
proposed 2 mechanisms for evolution (1809):
use & disuse – parts of the body that are used become larger and stronger whereas parts that are not used deteriorate
inheritance of acquired characteristics – modifications acquired during one’s lifetime can be passed to offspring

11. Darwin (1809-1882) descent with modification natural selection
organisms are related through descent from a common ancestor
as descendents of the ancestral organism encountered new habitats, they accumulated adaptations that fit them to specific ways of life
natural selection
differential success in reproduction among individuals that vary in their heritable traits

12. Figure 22.5 The voyage of HMS Beagle
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Marchena
Equator
SOUTH
AMERICA
Santiago
Daphne
Islands
Pinzón
AUSTRALIA
Fernandina
PACIFIC
OCEAN
Figure 22.5 The voyage of HMS Beagle
For the Discovery Video Charles Darwin, go to Animation and Video Files.
Isabela
Santa
Cruz
Andes
Cape of
Good Hope
Santa Fe
San
Cristobal
Tasmania
Florenza
Española
Cape Horn
New
Zealand
Tierra del Fuego

13. In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar
In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s
Darwin quickly finished The Origin of Species and published it the next year

14. On the Origin of Species (1859)
2 major points made by Darwin:
many modern species are descendents of ancestral species
the mechanism for this evolutionary process is natural selection:
a population can change over generations if individuals with certain heritable traits leave more offspring than others
result = evolutionary adaptation
the accumulation of inherited characteristics that enhance an organism’s ability to survive & reproduce in a specific environment

15. Natural Selection
OBSERVATION #1 – populations would grow exponentially if all individuals reproduced successfully
OBSERVATION #2 – but populations tend to stay stable in size
OBSERVATION #3 – resources are limited
INFERENCE #1 – production of more individuals than the environment can support leads to a struggle for existence within a population so only a fraction of individuals survive each generation
OBSERVATION #4 – variation exists among members of a population
OBSERVATION #5 – much of this variation is heritable
INFERENCE # 2 – individuals with inherited traits that increase their chances of survival are more likely to reproduce and leave more offspring
INFERENCE #3 – the unequal ability of individuals to survive & reproduce will lead to a gradual change in the population, with favorable characteristics accumulating over generations

16. Fig. 22-7
Figure 22.7 “I think . . .”

17. (a) Cactus-eater (c) Seed-eater (b) Insect-eater Fig. 22-6
Figure 22.6 Beak variation in Galápagos finches
(b) Insect-eater

18. Fig

19. Figure 22.8 Descent with modification
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Figure 22.8 Descent with modification
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa) 34 24
5.5 2
104
Millions of years ago
Years ago

20. Keys to Natural Selection
natural selection selects for adaptations already in existence (it doesn’t create new ones)
natural selection depends on time & place (what is advantageous in one situation may be useless or harmful in another)

21. (a) A flower mantid in Malaysia (b) A stick mantid in Africa
Fig
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa

22. Darwin’s theory helps explain…
homology – similarities between related species that are inherited from a common ancestor
homologous structures (similar structures with different functions)
anatomical similarities in vertebrate embryos
vestigial organs (remnants of structures that served important functions in an organism’s ancestors)
genetic code
genes & proteins
biogeography – geographic distribution of species
closely related species tend to be found in the same geographic region
(ex) most island species are similar to species on the nearest mainland rather than to species on distant islands with similar environments
fossil record
succession of life forms is consistent with “descent with modification”

23. Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Figure 22.9 Artificial selection
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi

24. Homologous Structures

25. Comparative Embryology

26. Vestigial Structures

27. Molecular Similarities