Evolution

Scientists and Experiments

• Describe the following scientists and their contribution to the development of evolutionary theory. Include a picture with your description.– Francesco Redi– Louis Pasteur– Urey & Miller– Jean Baptiste Lamarck– Charles Darwin

Early Earth• Earth is thought to be 4.6 billion years old.• Earth was “melted” by some catastrophic event.• Elements rearranged to make the layers of the

earth.• An atmosphere of hydrogen, nitrogen, carbon

dioxide and carbon monoxide formed. No free oxygen.

• Earth cooled and constant rain fell on the planet.• Lightning striking the atmosphere and waters

caused the formation of organic compounds.

Spontaneous Generation(abiogenesis)

• The idea that living things came from non-living substances.

• Disproving Spontaneous Generation:– Redi – Meat and maggots– Pasteur – Bacteria in broth

Biogenesis

• Life only arises from living things

Miller and Urey’s Experiment:• attempt to demonstrate how organic molecules could have first

appeared on early earth. They hypothesized that if the right materials were in the atmosphere, and they were struck by lightning, they might form organic compounds.

1.Simulation of a reducing atmosphere: Gas chamber containing a mixture of methane, ammonia, water and hydrogen. NO OXYGEN!

2.Liquid water.

3.Lightning strike simulated with an electric spark.

4.Amino acids began to form in a trap that caught water that dripped from the gas chamber.

The First Cells

• The first cells would have been heterotrophic.• The first cells were prokaryotic.• The first cells were anaerobic.

Endosymbiotic Theory

• Some prokaryotic cells that were autotrophic were taken in by heterotrophic cells, and they formed a mutualistic relationship. – These were the first cells with

chloroplasts.– These cells produced oxygen for

the atmosphere• Later, other cells took in

prokaryotic cells that carried out respiration. These were the first cells with mitochondria.– At first these cells were

anaerobic– Cells became aerobic when

oxygen was in atmosphere

Charles Darwin

• The Father of Evolution• Galapagos Islands• Adaptations ~ inherited characteristics that

enhance an organism’s chance of survival.

Darwin’s Theory of Evolution

• Individual organisms differ, and some of this variation is heritable

• Organisms produce more offspring than can survive, and many that do survive do not reproduce

• Because more organisms are produced than can survive, they compete for resources

• Individuals best suited to their environment survive and reproduce most successfully

• Species alive today are descended with modification from ancestral species that lived in the distant past

Galapagos Turtles and Finches

Darwin observed that the beak of finches on each island were adapted to the food sources available on each island.

Darwin observed that the curve of the shell of turtles on the Galapagos was adapted to the type of vegetation on each island.

Natural Selection

• The individual that is best adapted to its environment is most likely to survive, mate, and pass on its genes to offspring.

• “Survival of the Fittest”

Natural Selection (on a single gene trait)

• Can lead to changes in allele frequencies and thus to evolution

Polygenic traits & the bell curve

• Polygenic trait: trait controlled by two or more genes– Ex: height

What’s your shoe size?

• Bell curve

1 2 3 4 5 6 7 80

2

4

6

8

10

12

Directional selection

• Form of natural selection in which the entire curve moves

• Occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

• Selection favors one extreme trait value over another.

Example: peppered moths

Stabilizing Selection

• Form of natural selection by which the center of the curve remains in its current position

• Occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

• Selection favors the intermediate trait over the extreme traits.

Example: Baby weight in humans (Infants with average birth weight are more likely to survive than a baby that is too small or too large)

Disruptive Selection

• Occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

• Selection favors both extremes over the intermediate trait.

Example: Galapagos finches

Species

• A species is defined as a group of organisms that breed with one another and produce fertile offspring.– Individuals of a species share a common gene pool

Speciation

• The formation of a new species.• Process:– A population must diverge (disruptive selection)– Geographic isolation must occur to maintain the

divergence.– Reproductive isolation must occur so that the groups are

truly different species.

What must happen?

• Behavioral isolation: 2 populations are capable of interbreeding buy have differences in courtship rituals or other reproductive strategies that involve behavior

Ex: Eastern and western meadowlark live in some of the same areas but do not interbreed because they have different mating songs

Geographic Isolation

• 2 populations are separated by geographic barriers such as rivers, mountains, or bodies of water.

Colorado River now separates two squirrel species

Temporal Isolation

• 2 or more species reproduce at different times

– Example: 3 similar species of orchid all live in the same rain forest. Each species releases pollen only on a single day. Therefore, they do not pollinate one another.

Darwin’s Finches

• Speciation occurred in the Galapagos finches by – the founding of a new population: South America to

the Galapagos Islands– Geographic isolation: Movement of some birds to

another island– Changes in the gene pool: the isolation caused the

different finches to become adapted to their own environments (seed sizes favor different beaks)

– Reproductive isolation: prefer to mate with birds that have the same size beak

Adaptive Radiation• The evolution of several different forms from a

simpler ancestor.• Requires speciation and adaptation to different

habitats. • Model: Darwin’s finches– Common finch ancestor from mainland found island in

the Galapagos chain with many unoccupied niches.– Speciation occurred as the finch offspring adapted to

the new niches available. Many daughter species develop.

Evidences for evolution

• Homologous and Analogous Structures• Embryology• Fossils• Biochemistry

Homologous Structures

• Structures that are similar in composition, but have different functions.

Identify the similarities between these appendages.

Identify the different functions of these appendages.

Analogous Structures

• Structures that have similar function, but different composition.

Embryology• Embryology is the

study of embryonic development.

• Idea is that similarities between embryos are indicators of how closely related organisms are.

Fossils

• The order in which fossils are buried• first fossilized fish appear buried below the first fossilized

amphibians which appear below the first fossilized reptiles which appear below the first fossilized birds and mammals

• Transitional fossils: fossils which are thought to document the evolutionary change, or transition, of one species into another

Transitional fossils

Biochemistry

• Current theories look at how close genetic codes are to each other.

• The more similarities in the DNA of two organisms, the more closely related they are supposed to be.Remember: DNA to RNA to amino acids to proteins

Types of Evolution

• Divergent Evolution: The process by which an interbreeding population or species diverges into two or more descendant species, resulting in once similar or related species to become more and more dissimilar.

• Convergent Evolution: A kind of evolution wherein organisms evolve structures that have similar (analogous) structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.