Evolution

Chapter 15

Voyage of the Beagle

Darwin’s Adventures• Observations

– Darwin saw plants/animals and took notes

– Noted how well they were suited to their specific environment

– Had visited similar environments but did not see same species

– Why no kangaroos in England?– Many fossils he discovered resembled

living organisms but not identical

Galapagos Islands

• Close together, but different islands– Smallest were hot dry and barren– Largest greater rainfall

Shape of Shells

• Tortoises– Shell shape could determine which

island the tortoises inhabited

Birds of Galapagos

• Finches– Collected finches and studied their

beaks

An Ancient Changing Earth• Hutton

– Earth much older than a couple thousand years

– Mountains, valleys took thousands of years to form

• Lyell– Explain past events with observations– Caused Darwin to ask….if earth can

change over time then is it possible that organisms could as well

Jean Baptiste Lamarck• Noticed that blacksmiths were usually

muscular

• Noticed that their children would usually become muscular

• Hypothesized that being muscular was passed down from parent to offspring

• Used no scientific evidence

Jean Baptiste Lamarck• Use and Disuse of

Organs– Organisms constantly

strive to improve themselves to become more advanced/perfected

– The effort to improve causes the most used body structure to develop and the most unused structure to waste away

• Principle of Acquired Traits– The modified structure

can be passed down from parent to offspring

Jean Baptiste Lamarck

• Lamarck was disproved by August Weismann– Weismann cut off tails of over a 100 mice– mated the mice for 50 generations– all of the mice were born with tails

Malthus

• 1798…observed more babies born than people dying• Reasoned population continue to grow unchecked sooner or

later not enough resources to support all life• Darwin related this to plants/animals• All offspring could not have survived because continents

would be filled

Charles Darwin

• RECALL• Sailed on the Beagle as the ship’s

naturalist• Visited the Galapagos Islands• Then publishes “Origin of Species”

**Abandoned Lamark’s idea that species “perfected” themselves

Natural Variation and Artificial Selection

• Natural Variation- differences among individuals of a species– Some cows give more milk– Some plants bigger fruits– Some plants produce more peas

• Artificial Selection- picking which individuals can reproduce

Artificial Selection with Dogs

Charles Darwin• Darwin’s Theory:

– All organisms compete for limited space (Struggle for existence)– Organisms produce more offspring than

can survive (survival based on fitness)– Natural selection (survival of the

fittest)states that organisms best suited to the environment survive while those not suited may eventually die

Charles Darwin

Big PictureOver time natural selection results

in changes in the inherited characteristics of a population ****

Descent with Modifications………... As a result species look different from their ancestors

Types of Evolution• Divergent – related species become dissimilar• Extinction – disappearance of a species

– Ex dinosaurs• Adaptive Radiation – 1 species evolves into more species adapted

to surrounding– Ex Darwin’s finches

• Convergent evolution – unrelated species come to look alike due to evolving similar adaptations to similar environments– Ex penguins and dolphins

• Coevolution – 2 species evolve in response to change in each other– Ex plants evolved poison to protect themselves from insects and

insects evolved ways to protect themselves• Punctuated equilibrium – long periods of no change are interrupted

by short periods of rapid change

Types of Evolution

• Divergent– Related organisms become more distant

• ex: Grizzly Bears & Polar Bears

Types of Evolution

• Convergent– Distantly related organisms develop

similar characteristics• ex: Dolphins & Penguins

Evidence of Evolution

• Fossil Record• Geographic distribution of living

species• Homologous structures• Similarities of early development

Fossil Evidence• By examining fossils from,

sequential layers of rock one could view how a species had changed over time

Geographic Evidence• Little brown birds that all looked different were in

reality all finches• THIS IS DIFFERENT FROM:Evolution of shared traits in unrelated species because

of similar environments is called convergent evolution

Anatomical Evidence

• Analogous Structures– Body parts of different organisms that

have the same function but different structures

– ex: Bird’s Wing & Butterfly’s Wing

• Vestigial Structures– Body parts with no apparent functions– ex: human appendix, tiny hip bones in

some snakes

Homologous Structures• Notice similarities of similar structures• Each limb adapted in way to best fit the organism

in their environment• Strong evidence that 4 limbed animals with back

bone all descended, with modifications from common ancestor

Anatomical Evidence

• Homologous Structures– Body parts of

different organisms that have the same basic structure

• Example: Human Arm, Bird Wing, Whale Fin, Bat Wing

Similar Early Development

• Early stages are so similar that it is difficult to tell them apart

Embryological Evidence

• Study of early growth stages & development of embryos

• The embryos of different organisms look very similar– similar genes at work

• The DNA sequences which control early development remain unchanged because of little or no mutations

Summary of Charles Darwin

• Darwin’s Evolution:– Variation exists within a species– Some variations are favorable– Survival of the fittest

• The strongest will survive and reproduce• The weak will die out• Organisms better adapted to the

environment will survive

– Adaptations will happen gradually • Gradualism

Chapter 16

• Evolution of Populations

Remember Evolution

• Gradual change in characteristics over time

• A theory that explains how organisms change over a period of time

• Results in: – New organisms– Some organisms becoming extinct

Evolution

• Variations - differences in traits

• Adaptation - gradual changes to an organisms to help it survive

• Gradualism - the belief that evolutionary changes in organisms take several years to occur

Charles Darwin

• Natural Selection

Charles Darwin• Natural Selection:

– Disruptive Selection• Selection can act against the middle of a normal

distribution after an environmental change, this is selection against the most common variation (ex. African Swallowtale Butterfly

– Directional Selection• After several generations, the normal distribution shifts

in the direction of change (ex. DDT and insects)

– Stabilizing Selection• Environments may go through long periods of stability,

when conditions remain about the same. Organisms that are best adapted to the existing environment will be favored, and there is selection against the extremes

Speciation

• Speciation– When one or more new organisms

evolve from a single ancestral species

• Divergent Isolation– When an isolated population evolves into

different populations that cannot interbreed

Synthesis of Organic Molecules

• Miller & Urey– Mixed water vapor, methane, ammonia,

& hydrogen gas (all inorganic) together with electrodes (lightning)

– After a week they produced Organic Molecules

Prokaryotic to Eukaryotic• Origin of an inner membrane - Cell

membrane infolded to create compartments

• Endosymbiosis– Mitochondria and Chloroplast (free living

Prokaryotes) were consumed by a larger Prokaryote

– They were not digested and formed a permanent partnership - Symbiosis

Chapter 17

• The History of Life

Evidence of Evolution

• Fossil

• Anatomical

• Embryological

• Biochemical

Fossil Evidence

• Organisms became increasingly complex over time

• Types of fossils– Preserved Tissue– Preserved Trace

• Youngest fossils are on top, Oldest are on the bottom

How old are fossils?

• In sedimentary rock layers, the oldest fossils are in the bottom layers, the youngest fossils are in the top layers

• Radioactive dating & Carbon-14 dating

Population Genetics

• Population– Group of organisms that live in the same

are & interbreed

• Evolution can only occur when there is a change in the kinds or % of genes in the gene pool of a population (allele frequencies)

Hardy-Weinberg Principle

• Describes the conditions that must be met in order for the allele frequencies to remain constant

• It describes genetic equilibrium

• Five conditions

Hardy-Weinberg Principle• 1. No Mutations

• 2. Random Mating

• 3. No Genetic Drift

• 4. No Natural Selection

• 5. No Gene Flow