2 Evolution Mechanisms Evidences

1

Biology 1

Carmela Española

Room 107, IB Main Building

M 10-12AM

TTh 10-12AM & 3-5PM

Mechanisms and Evidences of Evolution

Evolution = process that changes the genes of

populations of organisms over time

“

”

Nothing in biology makes sense

except in the light of evolution.

Theodosius Dobzhansky: 1900-1975

It is a unifying concept in biology.

May be used to explain:

• Origin of species

• Diversity of organisms and their relationships

• Similarities and differences among species

• Adaptations to the environment

Terms

• Alleles – one of the alternative forms of the same genes

• Population – a group of individuals of a single species

inhabiting a certain area

• Adaptation – evolutionary process that changes

anatomy, physiology or behavior, resulting in an

increased ability to live in a particular environment,

happens in a POPULATION (not individual)

History of evolutionary thought

6th Century BC

• Greek philosopher Anaximander

• Proposed that life arose in water

• Simpler forms of life preceded

more complex form

2

18th Century AD

• French naturalist Georges-Louis Leclerc,

Comte de Buffon

• Predicted that the Earth is <6000 years

old and suggested that different species

may have arisen from common ancestors,

though he later argued against it.

• Father of biogeography


19th Century AD

• French naturalist Jean Baptiste

Lamarck

• Proposed the inheritance of acquired

characteristics

• Though erroneous, his idea provided

strong advocacy for the concept of

evolution


Lamarck’s inheritance of

acquired characteristics

(use and disuse theory)

19th Century AD

• British naturalist Charles Darwin

• Proposed together with Alfred

Wallace evolution by natural

selection

• Wrote On the Origin of the Species by

Means of Natural Selection


Theory of Natural Selection

• Organisms beget like organisms

• There are chance variations between individuals in a species. Some variations are heritable.

• More offspring are produced each generation that can be supported by the environment.

• Some individuals, because of their physical or behavioural traits, have a higher chance of surviving and reproducing.

19th Century AD

• Austrian monk Gregor Mendel

• Laid down the foundations of heredity.

• Showed that traits can be inherited in a

well-defined and predictable manner

• Darwin could not explain how his traits

that lend fitness can be inherited


3

Laws of Inheritance

Law of Segregation

• For each trait, there are two alleles that are

separated during gamete formation, to be joined

randomly during fertilization.

Law of Independent Assortment

• Different genes from different traits are passed

independently from parent to offspring.

20th Century AD

• Japanese biologist Motoo Kimura

• Proposed the neutral theory of

evolution

• The molecular changes represented by

majority of molecular differences do

not influence the fitness of the

individual organism.


20th Century AD

• American molecular biologist

James Watson and British

physicist Francis Crick

• Elucidated the structure of DNA

based on X-ray crystallography

data of Rosalind Franklin


20th Century AD

• American physician & medical

researcher Oswald Avery

• identified DNA as the genetic

material


Mechanisms for Evolution

Natural Selection

Gene Flow

Genetic Drift

Natural Selection

Result of differences in survival and reproduction

among phenotypes

4

The evolution of insecticide

resistance is an example of

natural selection in action

Chromosome with gene

conferring resistance

to insecticide

Additional

applications of the

same insecticide will

be less effective, and

the frequency of

resistant insects in

the population

will grow

Survivor

Insecticide

application

Natural selection, by its cumulative effects over vast spans of time, can produce new species from ancestral species.

What began as one species could gradually diversify into many species.

Key challenges to living organisms

• Find appropriate habitat and environmental conditions

• Obtain necessary resources

• Avoid predators

• Find a mate (or mates)

• Produce as many successful offspring as possible

Natural selection can act on any trait that affects any of

these challenges (http://www.bio.georgiasouthern.edu/)

Galapagos Finches

Gene Flow

Exchange of genes between populations, mostly of the

same species, and regulated by migrations

Gene FlowExchange of genes between populations,

mostly of the same species, and regulated by migrations

5

Genetic Drift

Change in gene frequencies in a population due to

chance or random events

Bottleneck EffectAn example of genetic drift at work

Bottleneck Effect and

Northern Elephant Seals

Hunting in the 1890s reduced

population to 20 individuals, resulting to

reduced genetic variation.

Their population has since rebounded

to 30,000

But the Bottleneck Effect is still

apparent when compared to less hunted

southern elephant seals

http://evolution.berkeley.edu/evosite/evo101/IIID3Bottlenecks.shtml

Founder EffectAn example of genetic drift at work

Evidences for Evolution

Microevolution

(below the species level)

• Artificial selection

• Genetic variation

maintained by natural

selection

Macroevolution

(at or above the species level)

• Fossil record

• Comparative anatomy

• Comparative

embryology

• Molecular biology

Evidence for evolution: MICROEVOLUTION (below the species level)

1. Artificial selection

• Plant and animal

breeding led to the

emergence of various

crop plants and

different breeds of

farm animals

6

Wild mustard

KohlrabiKale

CabbageBrussels sprouts

broccolicauliflower

2. Genetic variation maintained by

natural selection

• e.g. sickle-cell anemia

• ss – people with misshapen red blood cells

• Ss – people that are less susceptible to

malaria

• Presence of malaria in Africa acts as a

selection pressure to maintain the recessive

allele in the population


Sickle Cell and

Malaria

2. Genetic variation maintained

by natural selection

• e.g. British peppered moth Biston

belutaria

• During the Industrial Revolution,

white moths were nearly

decimated, either because they

were more susceptible to air

pollution or they were more

conspicuous to bird predators


http://www.seedfest.co.uk/seeds/kohlrabi/Kohlrabi.jpg

http://www.seedfest.co.uk/seeds/kohlrabi/Kohlrabi.jpg

7

1. Fossil Record • e.g. Archaeopteryx

• Discovered by

Von Mayer in

Germany

• Missing link

between reptiles

and birds


• e.g. Tiktaalik roseae

• Discovered by Edward B. Daeschler in Canada

• Missing link between non-tetrapod fishes and tetrapod amphibians


2. Comparative Anatomy

• Presence of

HOMOLOGOUS

STRUCTURES or

structures with the

same embryonic

origin


• Homologous structures must be

distinguished from ANALOGOUS

STRUCTURES or structures that resemble

each other physically or functionally but do

not have the same embryonic origin


3. Comparative Embryology

• Closely related organisms

have similar stages in

their embryonic

development


Embryonic development in vertebrates

• possess a dorsal, hollow nerve cord

• a notochord (stiffening rod of

cartilage) in the back

• similar membranes in the embryos

• yolk sac that produces the first blood

cells and germ cells

• similar development of many organs


8

Evidence for evolution:

MACROEVOLUTION (at or above the species level)

4. Molecular Biology

• Related individuals have greater similarity in their DNA and

proteins than do unrelated individuals

Patterns of Macroevolution

1. Divergent evolution

2. Convergent evolution

3. Parallel evolution


1. Divergent Evolution

• When two or more biological characteristics have a common

evolutionary origin but have diverged over evolutionary time

• Also known as ADAPTIVE EVOLUTION


2. Convergent Evolution

• Organisms not closely

related that

independently evolve

similar traits as a result

of having to adapt to

similar environments or

ecological niches

• Exemplified by

analogous structures


3. Parallel Evolution

• The independent evolution

of similar traits, starting from

a similar ancestral condition

• NOTE: When both

descendants are similar in a

particular respect, evolution is

defined as parallel if the

ancestors considered were

also similar, and convergent

if they were not.

9

Mechanisms and Evidences of

Evolution

Evolution = process that changes the genes of populations

of organisms over time

Mechanisms for Evolution

Natural Selection

Gene Flow

Genetic Drift

Evidences for Evolution

Microevolution

(below the species level)

• Artificial selection

• Genetic variation

maintained by natural

selection

Macroevolution

(at or above the species level)

• Fossil record

• Comparative anatomy

• Comparative embryology

• Molecular biology

Evolution

Fact or Theory?

Darwinism and the alternative views on the origin of life

Next meeting

Sources

• Slides were taken and modified from:

• Bio11 slides

• Bio12 slides

• Dr. Ma. Dolores Tongco

• Dr. Ian Fontanilla

• http://www.bio.georgiasouthern.edu/

• Photos were from the internet.

http://www.bio.georgiasouthern.edu/

Documents

2 Evolution Mechanisms Evidences