Chapter 22: Mechanisms of Evolution

Ms. KlinkhachornMarch 14, 2011

AP Biology

Homework

• Test Corrections – due Friday– Give the correct answer and explain why yours

was incorrect

We’re Running Out of Time!

28 days until the AP Exam

(12 more days until Jonisha’s birthday)

What this means

• Outside reading and packets• Essays for homework• Weekend/afterschool sessions• Online laboratories

Quick Write! (10 min)

1. Genes are located on chromosomes and are the basic unit of heredity that is passed on from parent to child, through generations.

a) Explain how a chromosome mutation could occur and why mutations are detrimental to the organism in which they take place

b) Explain why it is that – although there are very few genes located on the Y chromosome – human males may suffer from having just one copy of the X chromosome, whereas females have two

Evolution

• Evolution = descent with modification • Evolution = changes in the genetic

composition of a population from generation to generation

Historical Background

• The Old Testament says that species were individually designed by God and therefore perfect. – Scientists believed that the match of organisms to

their environment was evidence that God had created them for a particular purpose

Linnaeous and Cuvier

• Linnaeous – Grouped species by similarities based on patterns of their

creation• Developed taxonomy, how we name and classify organisms

• Cuvier– Developed the area of paleontology, the study of fossils– Observed that fossils that were deeper down looked less

similar to current life-forms– Opposed the idea of evolution and was a proponent of

catastrophism• Idea that past events were sudden (catastrophes) that destroyed

many species at one time

Fig. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

18091798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)Hutton (gradual geologic change)

Lyell (modern geology)Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

Lyell

• Lyell– Uniformitarianism says that mechanisms of

change are constant over time• Geologic processes that occurred in the past occur at

the same rate in the future

– Important because it indicates that Earth is old

Lamarck’s Hypothesis of Evolution

• Lamarck– the one other person besides Darwin to propose a

mechanism for HOW organisms actually changed– Believed in evolution, but didn’t get the process– Two guiding principles:

• Use and disuse – parts of the body that are used a lot get stronger, while those that aren’t used get weaker

• Inheritance of acquired characteristics – acquired characteristics can be passed on to the next generation

Charles Darwin

• Father of Evolution• Did most of his

observational studies on the Galapagos Islands off the coast of South America

• Focused on ideas of adaptation and natural selection

Adaptations

• Adaptations are characteristics of organisms that enhance their survival and reproduction in specific environments– Examples:

• Beak shape

• Darwin says that the descendants of the earliest organisms spread out to different habitats– Based on these habitats, they adapted differently

Fig. 22-6

(a) Cactus-eater (c) Seed-eater

(b) Insect-eater

Fig. 22-8a

Elephas maximus(Asia)

Stegodon

Mammuthus

Loxodontaafricana(Africa)

Loxodonta cyclotis(Africa)

010425.52434

Millions of years ago Years ago

Platybelodon

Natural Selection

• Survival of the fittest• Natural selection is the mechanism behind

evolution– Individuals that have characteristics better-suited

to the environment are able to have more offspring than others

– Over time, NS increases the match between organisms and their environment

– If an environment changes, NS will result in adaptations or new species

Fig. 22-12a

(a) A flower mantid in Malaysia

Fig. 22-12b

(b) A stick mantid in Africa

Misconceptions

• Evolution takes time. Populations evolve, not individuals.

• Natural selection only works for heritable traits– Acquired characteristics cannot be inherited

• Your work ethic is not encoded into your genes

• Favorable traits depend on the environment– Polar bears wouldn’t be happy at the equator

Evidence for Evolution

• Direct Observation• Fossil Record• Homology• Biogeography

Direct Observation - Guppies

• Adult male guppies are brightly colored– Females are more attracted– Predators are more attracted

• Observation: The more predators there are, the less colorful the males are– Hypothesis: intense predation caused natural

selection in male guppies, favoring drab colors

Fig. 22-13a

Predator: Killifish; preysmainly on juvenileguppies (which do notexpress the color genes)

Guppies: Adult males havebrighter colors than thosein “pike-cichlid pools”

Experimentaltransplant ofguppies

Pools withkillifish,but noguppies priorto transplant

Predator: Pike-cichlid; preys mainly on adult guppies

Guppies: Adult males are more drab in colorthan those in “killifish pools”

EXPERIMENT

Fossil Record

• By examining fossils, scientists can figure out similarities between organisms– Figure out ancestry

• Do radioactive testing to figure out the age of certain fossils– Can infer the age of other fossils

Fig. 22-15b

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

12

14

16

18

2

Dep

th (m

eter

s)

1

1

2

Fig. 22-16ab

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

Fig. 22-16cd

(c) Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

(d) Balaena (recent whale ancestor)

Homology

• Homology = similarity resulting from common ancestry– Species that are in some way

related have characteristics that are similar, though the function might be very different

• Example: Humans and chimpanzees share 99% of their DNA (and about 60% with a banana)

Homologous Structures

• Anatomical structures that are similar within organisms but may have different functions

• Example: arm of humans, cats, whale and bats

Embryonic Homology

• Studying the embryos of organisms can reveal anatomical homologies that aren’t visible in adults

• Example: All vertebrate embryos have a tail

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

Vestigial Structures

• “Leftovers” of features that used to serve an important function in a different time period

• Example:– Some whales have a pelvis and leg bones in their

skeleton• What does this indicate?

Evolutionary Tree

Hawks andother birds

Ostriches

Crocodiles

Lizardsand snakes

Amphibians

Mammals

Lungfishes

Tetrapod limbs

Amnion

Feathers

Homologouscharacteristic

Branch point(common ancestor)

TetrapodsAmniotes

Birds

6

5

4

3

2

1

Convergent Evolution

• Organisms can be distantly related but still share similar traits– Faced similar environmental challenges that

favored specific traits

• These are called analogous structures• Example:

– Penguins, dolphins, and sharks have torpedo-shaped bodies

Fig. 22-20

Sugarglider

Flyingsquirrel

AUSTRALIA

NORTHAMERICA

Biogeography

• Biogeography = geographic distribution of species– Species are more closely related to species within

their geographic area than species in distant areas

• Example: An animal found in the South American desert is more closely related to another SA desert animal than an African desert animal

Continental Drift

• Drift = slow movement of continents over time

• 250 million years ago, all of the Earth’s continents were one giant piece of land called Pangea

Application of Information

1. Graph the data found in the table

2. Examine the graph and hypothesize why the percentage of mosquitoes resistant to DDT rose rapidly

3. Suggest an explanation for the global spread of DDT resistance

Evidence for Evolution

• Direct Observation• Fossil Record• Homology• Biogeography