Chapter 15The Theory of Evolution

Chapter 15The Theory of Evolution

Section 15.1 Natural Selection and the Evidence for Evolution

Section 15.1 Natural Selection and the Evidence for Evolution

EvolutionWhat is evolution?• A change in a population over time• These changes is caused by many factors and are mapped out through fossils

Charles DarwinDarwin on HMS Beagle• Ships naturalist

A Little Help

Charles Lyell

Thomas Malthus

Increased food production leads

to increased populations!!

Geological changes on Earth take a long time and are always

occurring!!

Darwin continues his studies

• Many species produce large numbers of offspring

• Individuals struggle to compete in changing environmental conditions

• Only some individuals survive the competition and produce offspring

Charles Darwin???

Darwin tests Heredity

Artificial selection( 人工选择 ) :

• breeding organisms with

specific traits in order to

produce offspring with

identical traits

• Controlled by humans;

• Can produce fast changes

Pigeon Breeding

Natural Selection•Organisms with favorable variations survive, reproduce, and pass their variations to the next generation. •Traits are only favorable at that time and under specific conditions.

•No giant insects•No giant lizards •Humans do not have gills

•Controlled by nature•Slow process

Structural adaptations arise over time

• Mimicry( 拟态 ):a structural adaptation

that enables one species to resemble

another species.

Adaptations: Evidence for Evolution

– Camouflage( 伪装 ) ： an adaptation

that enables species to blend with

their surroundings

Adaptations: Evidence for Evolution

Physiological adaptations( 生理性适应 )can develop rapidly; “Micro-evolution”

Adaptations: Evidence for Evolution

Fossils ：• provide a

record of early life and evolutionary history.

• Even with holes in the record, scientists can fill in the gaps

Other Evidence for Evolution

• Homologous structures( 同源器官 ):

•structural features with a common

evolutionary origin

• Homologous structures can be

similar in arrangement, in

function, or in both.

Anatomy

Analogous structures( 同功器官 ):

•the body parts of organisms that

do not have a common evolutionary

origin but are similar in function

Anatomy

Vestigial structure

( 遗迹结构 ) ：

•a body structure in

a present-day

organism that no

longer serves its

original purpose,

but was probably

useful to an

ancestor

Anatomy

Biochemistry

• Similar organisms have similar cellular organelles and/or enzymes

• Living things use DNA as a genetic blueprint• Species in the 3 Domains use similar sized

ribosomes

Section 15.2 Mechanisms of EvolutionSection 15.2 Mechanisms of Evolution

• Population:

– Collection of members in a

species

– DNA explains the variation

among individuals of a

population

• Population genetics( 种群遗传学 )

– studies of the complex

behavior of genes in

populations of plants and

animals

Population Genetics and Evolution

Populations, not individuals,

evolve

Gene pool( 基因库 )

•picture all of the alleles

of the population’s genes

as being together in a

large pool

Allelic frequency( 等位基因频率 )

• the percentage of any

specific allele in the gene

pool

Population Genetics and Evolution

Hardy-Weingberg Equation: p + q = 1

• p = frequency of Dominate allele

• q = frequency of Recessive allele

• p2 + 2pq + q2 = 1

– 75 (RR) = 75 x 2 = 150 R

– 15 (R’R’) = 15 x 2 = 30 R’

– 10 (RR’) = 10 R and 10 R’

• 160 R and 40 R’

– 200 alleles total

• R alleles = 160/200 = 0.8 = p

• R’ alleles = 40/200 = 0.2 = q

Calculating Allele Frequency

AA= p2

2Aa = 2pqaa= q2

A a

A AA Aa

a Aa aa

100 flowers; 75 are Red, 15 are White, and 10 are Pink. What are the frequencies for alleles R and R’?

What are the genotype frequencies?RR= p2 = 0.82 = 0.64R’R’= q2 = 0.22 = 0.042RR’= 2pq = 2(.8)(.2) = 0.32

Genetic equilibrium( 遗传平衡 )

• The population is in genetic equilibrium when

the frequency of its alleles for specific trait is

the same in all its generations

Population Genetics and Evolution

1) Mutation( 突变 )

2) Gene flow( 基因漂流 )

• The transport of

genes by migrating

individuals

3) Genetic drift( 遗传漂变 )

•the alteration of allelic

frequencies by chance

events

All three have can huge

effects on small

populations

Changes in Genetic Equilibrium

Natural selection is usually the most significant

factor that causes changes in established gene

pools—small or large

3 Types of Natural Selection:

1) Stabilizing selection

-favors the average

2) Directional selection

-favors one extreme of a trait

3) Disruptive selection

-favors both extremes of a trait

Types of Natural Selection

Speciation( 物种形成 )

• The evolution of new species

• Members of similar populations no longer

interbreed to produce fertile offspring within

their natural environment.

The Evolution of Species

Polyploidy ( 多倍体 )

• any individual or species with a multiple

of the normal set of chromosomes

Causes of Speciation

Reproductive Isolation:

• Species no longer can

physically mate or

offspring are sterile

Behavioral Isolation:

• populations have

different mating

behaviors

Causes of Speciation

Gradualism( 渐变论 )

• species originate through

a gradual change; small

changes over a long time

Punctuated equilibrium( 骤变论 )

• speciation occurs

relatively quickly, in rapid

bursts, with long periods

of genetic equilibrium

Types of Evolution

Divergent evolution( 趋异进化 )

• species that once were similar

to an ancestral species

diverge, or become

increasingly distinct.

Adaptive Radiation( 适应辐射 )

• Ancestral species evolves into

many species to fit a number

of diverse habitats

Convergent evolution( 趋同进化 )

•distantly related organisms

evolve similar traits

Patterns of Evolution

That’s all !