Evolution

Charles Darwin (English Scientist )• Ideas 1st to be published• HMS Beagle – South America and South Pacific 5 year journey– Organism diversity led to curiosity about relations– Galapagos• Species-unique but similar• Led to idea of change over time (spent 22 years

studying)

• Ideas supported by fossil evidence

Galapagos Unique Adaptations

• Galapagos finch – Beak feed on Cacti

• Galapagos Tortoises– Largest in body size and shape

• Galapagos marine iguanas– Eat algae on ocean bottom (unusual food for

reptile)– Large Claws-slippery rocks

Charles Darwin• Base on Thomas Malthus idea “Human

population grows faster than Earth’s food supply” Darwin realized organisms:– Struggle to survive– Struggle for food– Compete for space– Escape predators– Find mates– Find shelter

Darwin and pigeons

• Breed and watched survival• Traits--vary depending on size and inheritance• Artificial Selection-breed organisms with

specific traits

Darwin and Natural Selection

• Mechanism for change in population• Organisms with certain variations, survive,

reproduce, and pass their variations to next generation.

• Organisms without variations less likely to survive and reproduce.

Natural selection gradual process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment.

Darwin-how species change over time

• Organism produce more organisms than can survive (fish millions of eggs)

• Individuals in a population have variations (different color, size, speed)

• Individuals with useful variations survive and pass traits (speed)

• Overtime-offspring with certain variations make up most of population and may look different from ancestors.

Darwin

Determined that species did not arise independently; rather species are

descendants of other species.

Alfred Russell Wallace

• Studied in Indonesia and Amazon River• Introduced Theory of Evolution• “Useful variations will tend to increase, un-

useful or hurtful variations to diminish”• Some qualities of an individual may allow it to

outlive another w/o qualities; pass qualities to offspring.

Lamarck’s Model

• Jean Baptiste de Lemarck• Individuals change due to environmental

influences; organisms adapt based on individual needs

• Acquired changes passed to offspring• “Use and disuse”- stronger is used; weaker if

not used; overtime modified due to use or disuse; disuse may disappear.

Relationship of work by Lamarck, Wallace and Darwin

• Darwin refuted Lamarck’s hypothesis that individuals change to meet needs due to environmental stress and that these acquired characteristics

• Wallace work overshadowed by Darwin; Now some celebrate Wallace more– Jointed presented to scientific community

Visualizing EvolutionEvolution difficult to observe– Short scale of human life– Contradictory to faith– Interpretations of data

Evidence for Evolution

• Structural• Physiological• Fossils• Anatomy• Embryology• Biochemistry

Structural adaptations

• Special structures and body parts• Mimicry• Camouflage

Structural Adaptations-develop over millions of years

• Size of teeth• Claws• fingers

Mimicry—Structural adaptations that enables one species to resemble another.

• Batesian- a species without any special defense mechanism mimics another species that predators avoid. (Same warning signs –coloring, pattern—no defenses—chemicals, spines)• Mullerian- more than one species with similar defense

mechanisms all have the same coloration (Same warning signs and same defenses)

Mullarian Mimicry-avoid being eaten; pass on genes

Camouflage

• Adaptation-blend in with surroundings

Darwin’s idea of natural selectionex Mole Rat

• Current animals probably resemble African rock rats

• Ancestors avoided predators-size of teeth and claws

• Ancestors survived passes variations to offspring

• Over time-modern mole rat—blindness evolved b/c no survival advantage.

Physiological Adaptations-(some rapid)

• Changes in metabolic process– Bacteria that resist antibiotics– Insects and weeds resistant to chemicals that kill

them.

Fossils

• Record of early life and evolutionary history

• Still incomplete record-jigsaw puzzle

• As become more complete, sequence of evolution more clear

Anatomy• Homologous

Structures-structural features with a common evolutionary origin

• Similar arrangement or function or both

Anatomy

• Analogous (aka “convergent”) Structures-Do not have common evolutionary (evolved independently) origin but similar in function

Anatomy

• Vestigial Structure-Body structure with no function in present day organism (ancestor’s may have used)– Eyes on blind mole-rat and cave fish– Forelimbs of ostrich

Embryo

• Earliest stage of growth and development of plants and animals.

• Similarities among young embryos suggest evolution from a distant, common ancestor.

Biochemistry

• DNA and RNA comparisons• Determine evolutionary relationships b/w

species• 1970s RNA and DNA nucleotide sequencing to

construct evolutionary diagrams.

Mechanism for Genetics and Evolution

• Genetics used to explain variation among individuals of a population

• Studies of the complex behavior of genes in populations-population genetics

• Populations, not individuals evolve.

Natural Selection acts on range of phenotypes in populations

Gene Pool All the alleles of the populations genes.

Allele frequency- Percentage of any specific allele in a gene pool.

Genetic equilibrium

Population in which the frequency of alleles remains the same over generations

• Affect small populations• Observed in small human populations that

have been isolated• Can result in an increase of an allele in a small

population (Amish)

Genetic Drift

Alteration of allelic frequencies by chance events

Disrupts Equilibrium

Genetic Equilibrium Disturbances

• Gene Flow-transport of genes by migrating individuals– Leaves-genes lost from gene pool– Enter-genes added to gene pool

• Mutations, genetic drift and gene flow may significantly affect the evolution of small and isolated gene pools (island)

• Natural selection most significant factor to change a gene pool.

Natural Selection acts on variations

• Variations can be inherited and they are controlled by alleles

• Allelic frequencies in a pop’s gene pool will change over generations due to natural selection.

• Three types of natural selection: Stabilizing, directional and distruptive

Stabilizing selection

• Natural selection that favors average individuals in a population

Directional Selection

• Natural selection favors one of the extreme variations of the trait

Disruptive selection

• Individuals with either extreme of a trait’s variation.

Speciation

• When members of similar populations no longer interbreed to produce fertile offspring within natural environment.– Geographic isolation– Reproductive isolation– Polyploid

Geographic isolation

• Physical barrier divides population– Prevents interbreeding between 2 groups

• Founders Effect