Charles Darwin

Evolutionary Thoughtand the

Evidence for Evolution

I.Evolution and Its Core Principles

A.Evolution is a central theme in biology-it explains striking similarities and astonishing differences in the form, function, behavior, and ecology of living things.

B.Core principles of evolution:

1. All life is linked through a common ancestor

2. Populations of living things change with time (evolve)

3. The environment influences this change (natural selection)

4. Helpful traits are selected over less-helpful traits and become more common in the population (descent through modification).

Charles DarwinCharles Darwin

A. Darwin’s contribution—Story of Darwin’s voyage of discovery. End to medical studies, studies theology, sets sail as naturalist on HMS Beagle along coastal South America.

II. Charles Darwin and the Theory of Evolution

B.Rich diversity of tropical life, mainland & island species, makes deep impression on young Darwin.

Darwin’s VoyageDarwin’s Voyage

Galapagos IslandsGalapagos Islands

C. C. Darwin’s Theory of Evolution by Darwin’s Theory of Evolution by Natural Selection Natural Selection

1. There is variation within a population

2. Some variations are helpful (allow organism to survive to pass on genes)

3. Some variations are NOT helpful (keep the organism from surviving and passing on genes)

4. Not all young produced in a generation can survivea. This leads to a struggle for

existence.b. Survival of the fittest.c. Those that survive and

reproduce are those with the good variations.

D. What is aD. What is a SPECIESSPECIES??

1. Group of similar organisms

a. Structurallyb. Biochemically

2. Can interbreed successfully in nature

a. Offspring are healthyb. Offspring are fertile (can reproduce)

THIS CAN’T HAPPEN, PEOPLE!!!

THIS CAN!

E. This organisms is not a new E. This organisms is not a new species…Why? species…Why?

Mule

F. Origin of SpeciesF. Origin of Species

Speciation – evolution of one or more species from a single ancestor species. can be from:

Isolation –geographic barrier (canyon, mountain, or island) separates 2 groups of the same species and they evolve separately.

G. Variation and AdaptationG. Variation and Adaptation

1. Variation – differences between individual members of a population

• Members of a species are very similar, but differences can be observed, making each individual unique.

• May be caused by mutations

2. Mutations• Changes in DNA base

sequences Most are either neutral or harmful (rarely beneficial)

Those that allow the organism to survive better in a particular environment are good & are more likely to be passed on to future

generations.

3. Most 3. Most variationsvariations are not are not caused caused by mutations by mutationsA. Sexual reproduction combines

genes from both parentsB. Crossing over during meiosis can

produce variations                                      

4. Adaptation4. Adaptation

a. An inherited trait that increases the population’s chances of survival & reproduction in a particular environment.

b. Allows organisms to fit best into a particular niche

(habitat and role)

H. Divergent EvolutionH. Divergent Evolution

Isolated populations of a species evolve independently of each other.

Ex: polar bears and brown bears

I. Convergent EvolutionI. Convergent Evolution• Natural Selection produces analogous (similar)

adaptations in different organisms in response to similar environments:

Ex: African Serval cat & South American maned wolf•These animals have similar ears, legs, acute

hearing, habitat, and Occupy similar niches

J. CoevolutionJ. Coevolution

Species that interact closely often adapt to one another:

K. Adaptive RadiationK. Adaptive Radiation•Many different species evolve

from one ancestral species – each new species has a different niche

III.Evolutionary Thinking before Darwin

A.Rapid advances in new field of geology (spurred by need to find coal and iron to fuel Industrial Revolution) set stage for Darwin’s ideas.

B. Other biologists have an influence:1.Darwin reads Lyell’s Principles of Geology; stressed antiquity of Earth’s history and its continual shaping by natural forces (evolution of land forms).

2.Lamarck’s ideas about inheritance of acquired characteristics were wrong, but notion of change in organism over time was sound.

Jean Baptiste LamarckJean Baptiste Lamarck

•Use and Disuse•Inheritance of

AcquiredCharacteristics

IV. Darwin’s Insights

A.Tour of Galapagos Islands impresses Darwin with its diversity; striking correlation between form of finch species and their environments; similarities and differences with mainland species lead to first flash in inspiration:

Darwin’s finches

Maybe the island species are derived from mainland species and have become different over time because of a change in the environmenton the islands.

B.Back in England, Malthus’ book on limits to population growth has strong impact (struggle for existence, preservation of good traits, loss of bad traits).

C.Wallace’s letter outlining basic principles of natural selection spurs Darwin into taking his ideas public.

D. After fierce debate, Darwin’s thesis that organisms evolve over time in response to natural forces is accepted among most scientists about 15 years after publication of On the Origin of Species by Means of Natural Selection.

(“Means” of natural

selection are debated

into modern times.)

E. Advances in genetics in the twentieth century yield the mechanism (DNA) through which natural selection operates, vindicating Darwin’s ideas.

V. Opposition to the Theory of Evolution

A. Evolutionary theory, more than any other scientific theory, is regularly challenged.

B. Much of the objection comes from a mistaken view of what a scientific theory represents.

C.Some of the evidence for evolution is historical in nature, and cannot be demonstrated experimentally; consistency in the evidence derived from many sources:

Biology: embryology, bio-chemistry

Other disciplines: geology, nuclear chemistry

More than 100 years of evidence has convinced most scientists that the core principles of evolution accurately describe the story of life on Earth.

VI. The Evidence for Evolution A. Fossils

1.The age of fossils found in

sedimentary rocks can

be determined using radioactive decay.

2. Fossils of simpler organisms are found in older rocks, newer rocks contain more complex organisms

Fossil FormationFossil Formation

B.Comparative morphology and embryology — Similarities in form and structure (morphology) between otherwise different-appearing structures, that is organization of bones in fins of whales, wings of bat, paws of cat and gorilla, point to their common evolutionary origin (homology);

Early embryo development in all animals goes through similar stages, to the extent of producing structures not seen in adults of the more complex organisms (e.g., pharyngeal slits in humans).

Comparative EmbryologyComparative Embryology

C. Homologous Structures – similar C. Homologous Structures – similar morphology, even if function is morphology, even if function is different, indicates a different, indicates a closeclose evolutionary relationshipevolutionary relationship

D. D. Analogous StructuresAnalogous Structures – – demonstrate organisms are demonstrate organisms are notnot related evolutionarilyrelated evolutionarily – similar – similar function, different morphology function, different morphology

BAT WING INSECT WINGS BIRD WING

E. Advances in molecular biology reveal similarity in genes that control cellular function in very different organisms (same set of genes controls many early events in the development of the fruit fly and mouse); gene sequence of more distantly related organisms more different; rate of accumulation of gene mutations since split from common ancestor may allow one to deduce how long ago two groups of organisms diverged from each other.

F. Experimental evidence can demonstrate natural selection at work;

Endler’s experiments with guppies: In predator-free environments there’s an increase in number of male guppies with large and brightly colored tails, because they are favored by females; but when predators are reintroduced the number of male guppies with smaller, less conspicuous tails increases again because the flashier fish are eaten by predators.

G. Evolution Observed: G. Evolution Observed: Peppered Peppered Moths Moths

Light moths

Dark moths

Light tree Dark tree

Less pollution More pollution

EvolutionEvolution