Descent with Modification – A Darwinian View of Life

Chapter 22

A.P. Biology

Liberty Senior High School

Rick L. Knowles

• Concept 1.4: Evolution accounts for life’s unity and diversity

• The history of life– Is a saga of a changing Earth billions of years old

Figure 1.17

Theodosius Dobzhansky

“Nothing in biology makes sense except in the light of evolution.”

The American Biology Teacher (1973)

• Overview: Darwin Introduces a Revolutionary Theory

• A new era of biology began on November 24, 1859– The day Charles Darwin published On the Origin of

Species by Means of Natural Selection

Charles Darwin, 1831, age 22, starting his voyage on the HMS Beagle

• Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

• In order to understand why Darwin’s ideas were revolutionary– We need to examine his views in the context of other

Western ideas about Earth and its life

• The historical context of Darwin’s life and ideas

Fig. 22.2

The Scale of Nature and Classification of Species

• The Greek philosopher Aristotle– Viewed species as fixed and unchanging

• The Old Testament of the Bible– Holds that species were individually designed by

God and therefore perfect– “Intelligent Design”

• Carolus Linnaeus– Interpreted organismal

adaptations as evidence that the Creator had designed each species for a specific purpose

– Was a founder of taxonomy, classifying life’s diversity “for the greater glory of God”

– Viewed species similarities not as evolutionary relationship, but as patterns of creation.

Carolus Linnaeus, 1707 -1778

Fossils, Cuvier, and Catastrophism• The study of fossils

– Helped to lay the groundwork for Darwin’s ideas

• Fossils are remains or traces of organisms from the past– Usually found in sedimentary rock, which appears in

layers or strata

Figure 22.3

• Paleontology, the study of fossils– Was largely developed by French scientist Georges Cuvier– Observed that upper strata were younger and lower strata

were older– Noticed that new species would appear in an older strata

and then disappear in a newer strata.

• Cuvier opposed the idea of gradual evolutionary change– And instead advocated catastrophism, speculating that each

boundary between strata represents a catastrophe (flood or drought).

Theories of Gradualism• Gradualism

– Is the idea that profound change can take place through the cumulative effect of slow but continuous processes.

– 1795, James Hutton proposed that Earth’s geologic features could be explained by gradual mechanisms currently operating (ex. valleys are created by rivers)

• Geologists Hutton and Charles Lyell– Perceived that changes in

Earth’s surface can result from slow continuous actions still operating today

– Lyell proposed uniformitarianism – same geologic processes are operating today as in the past and at the same rate.

– Exerted a strong influence on Darwin’s thinking

Charles Lyell, 1797-1875

One of the First “Ideas” of Evolution• Lamarck compared

species today with the fossil record.

• 1809, hypothesized that species evolve through use and disuse and the inheritance of acquired traits.

• Organisms have an innate drive to become more complex.

• But the mechanisms he proposed are unsupported by evidenceJean-Baptiste de Lamarck, 1744 - 1829

Lamarck’s View of Evolution

•Plants and animals changed over time through the use and disuse of certain characteristics.•These acquired characteristics were inherited by the next generation.•No support for this notion.

Darwin and the HMS Beagle• During his travels

– Darwin observed and collected many specimens of South American plants and animals

• Darwin observed various adaptations of plants and animals– That inhabited many diverse

environmentsCharles Darwin, 1831, age 22, starting his voyage on the HMS Beagle

Fig. 22.5 The Voyage of the HMS Beagle

Name Two (2) Observations that Darwin Made Leading to His

Theory.Name One (1) Observation

We’ve Since Made About the Natural World.

Darwin’s Observations about Evolution

• 1. Fossil Record: noticed that the fossils of South America resembled living species of that continent.

• Example: Glyptodon related to modern armadillo?

Glyptodon

Modern Armadillo, Omaha Zoo, 2009

Darwin’s Observations of Evolution• 2. Biogeography – plants and animals in

temperate regions of South America resemble tropical species in South America than the temperate species in Europe.

• The distribution of life across similar climates is not always the same; (climate alone is not causing diversity).

• Closely related species are found in same geographic region.

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

Figure 22.17

• Different geographic regions, different mammalian “brands”– Have evolved independently from different ancestors

Marsupial Mammal

Placental Mammal

Charles Darwin, 1835, Galapagos

What’s so special about a bunch of islands?

National Geographic SeriesGalapagos, Tape #254

Darwin’s Finches

The Galapagos Archipelago

Bartoloma Island

Isabela Island

• Darwin proposed that natural selection

– Could enable an ancestral species to “split” into two or more descendant species, resulting in a “tree of life”

Large

ground finchSmallground

finch

Geospiza

magnirostris

Seed eater

Sharp-beaked

ground finch

Camarhynchus

psitacula

Green

warbler

finch

Large

tree finchLarge cactusground finch

Ground finches Tree finches

Insect eaters Bud eater

Warbler finches

Common ancestor fromSouth American mainland

Gray

warbler

finch

Certhidea

olivacea

Certhidea

fuscaGeospiza

difficilis

Cactus flowereater

Geospizascandens

Seed eater

Geospiza

conirostris

Geospiza

fortis

Mediumground

finch

Geospizafuliginosa

Mangrovefinch

Cactospiza

heliobates

Cactospizapallida

Woodpecker

finch

Mediumtree finch

Camarhynchuspauper

Small tree finch

Vegetarianfinch

Camarhynchusparvulus

Platyspizacrassirostris

Cactusground finch

Figure 1.23

Large

ground finch Smallground

finch

Geospiza

magnirostris

Seed eater

Sharp-beaked

ground finch

Camarhynchus

psitaculaGreen

warbler

finch

Large

tree finchLarge cactusground finch

Ground finches Tree finches

Insect eaters Bud eater

Warbler finches

Common ancestor fromSouth American mainland

Gray

warbler

finch

Certhidea

olivacea

Certhidea

fuscaGeospiza

difficilis

Cactus flowereater

Geospizascandens

Seed eater

Geospiza

conirostris

Geospiza

fortis

Mediumground

finch

Geospizafuliginosa

Mangrovefinch

Cactospiza

heliobates

Cactospizapallida

Woodpecker

finch

Mediumtree finch

Camarhynchuspauper

Small tree finch

Vegetarianfinch

Camarhynchusparvulus

Platyspizacrassirostris

Cactusground finch

Figure 1.23

Seen one tortoise, you’ve seen them all?

Dome-shaped Carapace Saddle-shaped Carapace

Galapagos Tortoise Distribution

Galapagos tortoise distribution, Galapagos Islands. Redrawn from Iverson (1992).

Galapagos Tortoise-Env. Club 2008, Omaha Zoo

Darwin’s Focus on Adaptation• Years later, Darwin

reassessed all that he had observed during the voyage of the Beagle

• He began to perceive adaptation to the environment and the origin of new species as closely related processes

Fig. 22.6

Alfred Russel Wallace, 1823-1913

•Explored Indonesia and southeast Asia, from 1854-1861, •Observed Tigers, Orangs, and Rhinos, Oh My!

Sumatran Rhino

Indian Rhino

Javan Rhino

Other Observations about Evolution• 3. Artificial Selection - humans have modified

other species over many generations by selecting and breeding individuals that possess desired traits

Fig. 22.10

• The Origin of Species articulated two main points…

– Descent with modification

– Natural selection

Figure 1.19

Natural Selection• Darwin proposed natural selection

– As the mechanism for evolutionary adaptation of populations to their environments

Populationof organisms

Hereditaryvariations

Differences in reproductive success

Evolution of adaptationsin the population

Overproductionand struggle for

existence

Figure 1.20

• Natural selection is the evolutionary process that occurs…– When a population’s heritable variations are exposed

to environmental factors that favor the reproductive success of some individuals over others.

1 Populations with varied inherited traits

2 Elimination of individuals with certain traits.

3 Reproduction of survivors.

4 Increasing frequency of traits that enhance survival and reproductive success. Figure 1.21

The Origin of Species

• Darwin developed two main ideas– Evolution explains life’s unity and diversity– Natural selection is a cause of adaptive evolution

• The phrase descent with modification– Summarized Darwin’s perception of the unity of life– States that all organisms are related through descent

from an ancestor that lived in the remote past

Elephant Phylogeny

Fig. 22.7

Summary of Natural Selection• Natural selection is differential success in

reproduction– That results from the interaction between individuals

that vary in heritable traits and their environment

• If an environment changes over time– Natural selection may result in adaptation to these

new conditions

• Over time natural selection can produce an increase

– In the adaptation of organisms to their environment

Fig. 22.11

• Concept 22.3: Darwin’s theory explains a wide range of observations

• Darwin’s theory of evolution– Continues to be tested by how effectively it can account for

additional observations and experimental outcomes– Natural Selection in Action – Evolution continues today!

• Guppies• HIV• Humans

Differential Predation in Guppy Populations

• Researchers have observed natural selection– Leading to adaptive evolution in guppy populations

Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools and measured the average age and size of guppies at maturity over an 11-year period (30 to 60 generations).

EXPERIMENT

Pools with killifish,but not guppies priorto transplant

Experimentaltransplant ofguppiesPredator: Killifish; preys

mainly on small guppies

Guppies:Larger atsexual maturitythan those in“pike-cichlid pools”

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in “killifish pools”

Figure 22.12

RESULTS After 11 years, the average size and age at maturity of guppies in the transplanted populations increased compared to those of guppies in control populations.

161.5185.6

67.5

Wei

ght o

f gu

ppie

sat

mat

urit

y (m

g)

Age

of

gupp

ies

at m

atur

ity

(day

s)

92.3

48.5

Control Population: Guppiesfrom pools with pike-cichlids as predators

Experimental Population:Guppies transplanted topools with killifish aspredators

76.1

Males Females

85.7

58.2

Males Females

CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered selection pressure resulted in an observable evolutionary change in the experimental population.

The Evolution of Drug-Resistant HIV

• In humans, the use of drugs– Selects for pathogens that through chance mutations

are resistant to the drugs’ effects

• Natural selection is a cause of adaptive evolution

Anatomy of HIV

Inside HIV

• Researchers have developed numerous drugs to combat HIV

– But using these medications selects for viruses resistant to the drugs

Figure 22.13

New Evidence that Darwin Did Not Have

• How old did most 19th Century people believe the Earth was?

• About 6,000 years old (Cuvier’s young Earth)

• 1. Age of the Earth- 4.5 billion year old. Better dating techniques than in Darwin’s time; more complete fossil record.

2. Transitional Species• Have intermediate characteristics of

two groups of animals – may represent a link in evolution (missing link?).

• Changes in structures may be small – difficult to identify in fossils.

• Species replaced quickly – not common in fossil record.

Archaeopteryx (150 million years ago)

Archaeopteryx

Archaeopteryx at the KU Natural History Museum

Evolution Happens in Small Steps

Show me the frogs!

Discover- Weird Nature: Marvelous Motion, tape #55

Other Transitional Examples?

Rodhocetus balochistanensis

Modern Whales

A Walking Whale?

Ambulocetus natans

Transitional Skulls

Rodhocetus Foot

Transitional Diatoms in Yellowstone

3. Vestigial Structures• Existing structures that have no

apparent function, but resemble structures of presumed ancestors.

• Examples: human appendix; muscle set in humans for moving ears;

The “Pelvis” of a Whale

Evidence of Transitional Species Today!

Vestigial Structure- blue whales with femurs?

Life of Mammals-Return to the Water video, tape #110

Vestigial Organs in Humans?

Structures of little or no use but may represent historical remnants of

structures that had important functions in ancestors.

Vermiform Appendix

Goosebumps?

Vomeronasal or Jacobson’s Organ

“Junk”DNA; L-gulonolactone oxidase gene

Extra Ear Muscles – auriculares muscles

Plantaris Muscle – 9% don’t have it

Wisdom Teeth – mandible becoming smaller

Third Eyelid – Plica semilunaris

Darwin’s (Auricular) Tubercle – only 10.4% have it.

Coccyx

Four-Finned Dolphin; Oct, 2006

Divers hold a bottlenose dolphin which has an extra set of human palm-sized fins near its tail in Taiji, Wakayama prefecture in western Japan.

-USA Today, Nov. 6, 2006

Four-Finned Dolphin; Oct, 2006

Divers hold a bottlenose dolphin which has an extra set of human palm-sized fins near its tail in Taiji, Wakayama prefecture in western Japan.

-USA Today, Nov. 6, 2006

Show me more vestigial structures!

Do snakes have “feet”?

The story of boas and pythons.

4. Anatomical Homologies• Homologous structures between organisms

– Are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor

Figure 22.14Human Cat Whale Bat

Homology• Homologous Structures – structures in different

species that are similar because of commons ancestry.

Sophie and a Mosasaur

• Analogous Structures – similarity in structures due to adaptations from similar evolutionary pressures (convergent evolution) and not a common ancestor.

Analogy

• The products of natural selection– Are often exquisite adaptations of organisms to

the special circumstances of their way of life and their environment

Figure 1.22

5. Comparative Embryology– Reveals additional anatomical homologies not

visible in adult organisms

Figure 22.15

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

Show me an example of homologous structures!

Compare a human hand and bat wing.

Life of Mammals- Life in the Trees video, tape

#110

6. Molecular Homologies• Biologists observe

homologies among organisms at the molecular level– Genes and proteins

that are shared among organisms inherited from a common ancestor.

Fig. 22.16

Darwin’s Theory of Evolution

• Natural selection is the driving force of changes within species populations.

Can we see evolution?

• Weiner, J. 1994. The Beak of the Finch. Knopf, New York.

• The video “What Darwin Never Saw”

I want to see evolution in action!

Scientific American Frontiers-Voyage to the

Galapagos, 2000, VT 551.4 SCI