1. Descent with Modification: A Darwinian View of Life
Chapter 22
Descent with Modification: A Darwinian View of Life

2. Overview: Endless Forms Most Beautiful
A new era of biology began in 1859 when Charles Darwin published The Origin of Species
The Origin of Species focused biologists’ attention on the great diversity of organisms
Darwin noted that current species are descendants of ancestral species
Evolution can be defined by Darwin’s phrase descent with modification
Evolution can be viewed as both a pattern and a process
Three observations about life
Organisms are suited for life in their environments
Organisms share many characteristics
Organisms show a great diversity

3. Figure 22.1 How can this beetle survive in the desert, and what is it doing?

4. 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
Isabela
Figure 22.5 The voyage of HMS Beagle
For the Discovery Video Charles Darwin, go to Animation and Video Files.
Santa
Cruz
Andes
Cape of
Good Hope
Santa Fe
San
Cristobal
Tasmania
Florenza
Española
Cape Horn
New
Zealand
Tierra del Fuego

5. (a) Cactus-eater (c) Seed-eater (b) Insect-eater
Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes
Figure 22.6 Beak variation in Galápagos finches
(b) Insect-eater

6. The Origin of Species Darwin developed two main ideas:
Descent with modification explains life’s unity and diversity
Natural selection is a cause of adaptive evolution

7. Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection

8. Artificial Selection, Natural Selection, and Adaptation
Darwin then described four observations of nature and from these drew two inferences

9. Fig
Observation #1: Members of a population often vary greatly in their traits
Figure Variation in a population

10. Observation #2: Traits are inherited from parents to offspring

11. Fig
Observation #3: All species are capable of producing more offspring than the environment can support
Spore
cloud
Figure Overproduction of offspring

12. Observation #4: Owing to lack of food or other resources, many of these offspring do not survive

13. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
This process explains the match between organisms and their environment

14. Natural Selection: A Summary
Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals
Natural selection increases the adaptation of organisms to their environment over time
If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species
Figure Camouflage as an example of evolutionary adaptation

15. Natural Selection: A Summary
Note that individuals do not evolve; populations evolve over time!!!!!!!
Natural selection can only increase or decrease heritable traits in a population
Adaptations vary with different environments
What is the ultimate source of genetic variation?

16. Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence
One example includes the evolution of drug-resistant HIV

17. 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 a greater reproductive success and increase in number relative to the susceptible viruses
The population of HIV viruses has therefore developed resistance to 3TC
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

18. Fig
100
Patient
No. 1
Patient No. 2 75
Percent of HIV resistant to 3TC 50
Patient No. 3
Figure Evolution of drug resistance in HIV 25 2 4 6 8 10 12
Weeks

19. The Fossil Record 2
The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time
The red dot shows change over time in the location and angle of the spines 4 4 6 4
Bristolia insolens 8 3
Bristolia bristolensis 10 12 3
Depth (meters) 2
Bristolia harringtoni 14 16 18 1
Bristolia mohavensis 3
Figure Fossil evidence of evolution in a group of trilobites 2 1
Latham Shale dig site, San
Bernardino County, California

20. Fig
The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record
Paleontologists have discovered fossils of many such transitional forms
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Figure The transition to life in the sea
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)

21. Vestigial structures are remnants of features that served important functions in the organism’s ancestors

22. Homology is similarity resulting from common ancestry
Humerus
Radius
Ulna
Carpals
Metacarpals
Figure Mammalian forelimbs: homologous structures
Phalanges
Human
Cat
Whale
Bat
Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

23. Comparative embryology reveals anatomical homologies not visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Figure Anatomical similarities in vertebrate embryos
Chick embryo (LM)
Human embryo

24. Blocks of similar sequences in four mouse chromosomes:
Fig
Human chromosome 16
DNA sequences very similar to large blocks of human chromosome 16 are found on mouse chromosomes 7, 8, 16, and 17. This suggests that the DNA sequence in each block has stayed together in the mouse and human lineages since the time they diverged from a common ancestor.
Blocks of DNA
sequence
Blocks of similar sequences in four mouse chromosomes: 7 8 16 17
Figure Similar blocks of sequences on human and mouse chromosomes
Duplication, rearrangement, and mutation of DNA contribute to genome evolution

25. Concept 21.6: Comparing genome sequences provides clues to evolution and development
The Darwinian concept of an evolutionary tree of life can explain homologies
Evolutionary trees are hypotheses about the relationships among different groups
Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
Fig – This tree diagram shows the ancient divergence of bacteria, archaea, and eukaryotes. A portion of the eukaryote lineage is expanded in the inset to show the more recent divergence of three mammalian species.

26. Bacteria Most recent common ancestor of all living things Eukarya
Fig
Bacteria
Most recent
common
ancestor
of all living
things
Eukarya
Archaea 4 3 2 1
Billions of years ago
Chimpanzee
Figure Evolutionary relationships of the three domains of life
Human
Mouse 70 60 50 40 30 20 10
Millions of years ago

27. Convergent evolution does not provide information about ancestry NORTH
Fig
Convergent evolution is the evolution of similar, or analogous, features in distantly related groups
Analogous traits arise when groups independently adapt to similar environments in similar ways
Convergent evolution does not provide information about ancestry
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Figure Convergent evolution
The ability to glide evolved independently in these two distantly related groups of mammals
Flying
squirrel

28. Fig. 26-7
An elongated body, enlarged front paws, small eyes, and a pad of thickened skin that protects a tapered nose all evolved independently in the marsupial Australian “mole” (top) and a eutherian North American mole (bottom).
Figure 26.7 Convergent evolution of analogous burrowing characteristics

29. Biogeography
Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution
Islands have many endemic species that are often closely related to species on the nearest mainland or island
Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift (this term outdated, plate tectonics is now the proper term)
An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved

30. Mid Ocean Ridge