Mechanisms of Evolution

Ms. KlinkhachornMay 17, 2011

Biology

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

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– Improve function– Examples:

• Beak shape • Behavior that allows prey to better avoid predators• Produces protein that works more efficiently

Fig. 22-6

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

(b) Insect-eater

Fig. 22-12a

(a) A flower mantid in Malaysia

Fig. 22-12b

(b) A stick mantid in Africa

Natural Selection

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

evolution– Individuals that have characteristics better-suited

to the environment (adaptations) are able to survive and thus, 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

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 so you cannot pass it on genetically

• 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

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14

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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

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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