C15-Theory of Evolution Pp Sharp Honors Biology

Contents  15-1  Natural Selection and the Evidence for Evolution  15-2  Mechanisms of Evolution Mechanisms of Evolution

Theory of Evolution  Charles Darwin ( ) English scientist whose observations as a young man of 22 aboard the HMS Beagle were the basis for his theory of evolution.  Five-year scientific journey as naturalist took him around the world collecting specimens and fossils.  On the Galapagos Islands, the many species suggested change

Theory of Evolution  On the Galapagos Islands, the many species suggested the possibility of change over time; however, he had no explanation of how this occurred.

Theory of Evolution  Darwin continued his studies for another 20 years.  Read economist Thomas Malthus ideas regarding survival of the fittest & adapted it.  Conducted pigeon breeding experiments with artificial selection. His study at Down House

Darwin Explains Natural Selection  Natural Selection is a mechanism for change in populations. It occurs when organisms with favorable variations survive, reproduce, and pass on their variations to offspring.  Seen here, Galapagos finch species varied by nesting site, beak size, and eating habits.

r  Soon Alfred Russel Wallace wrote Darwin a letter expressing similar thoughts.  In 1859, Darwin published On the Origin of the Species by Means of Natural Selection.  His ideas have become the basic unifying theme of modern biology.

Evidence Since Darwin  Structural Adaptation  Homologous structures  Comparative Embryology  Molecular Record (DNA)  Physiological Change i.e. antibiotic resistance  Fossil Evidence  Biochemistry

Adaptations: Evidence for Evolution  Any variation that aids an organisms chance of survival in its environment.  Structural adaptations arise over time.  Mimicry enables one species to resemble another.  Camouflage enable species to blend with background

Adaptation: Physiological  Some adaptations develop rapidly.  Bacteria develop resistance to antibiotics by changing their metabolic processes.  Also observed with pests and weeds responding to insecticides and herbicides.

Other Evidence for Evolution  Fossils  As the fossil record becomes more complete, the sequences of evolution become more clear.

Anatomy: Homologous Structures  Homologous Structures

Anatomy: Homologous Structures  The bones of each forelimb are modified for function, but they are arranged similarly.  Analogous Structures are similar in function but do not have a common evolutionary relationship.

 Add your conclusions here. Conclusion

Anatomy: Vestigial Structures  A body structure that no longer serves its original purpose.  Human ear muscles?  Appendix?  Whale hip bones?  Blind Cavefish?

Embryology  An embryo is the earliest stage of development of a plant or animal.  Shared features in the young embryo suggest evolution from a distant common ancestor. Fish Turtle BirdDog

Biochemistry  Nearly all organisms share DNA, ATP, and many enzymes such as cytochrome c.  Organisms that are biochemically similar have more amino acid sequences in common.  Used to interpret evolutionary relationships btw species. Can you fill in the missing sequences?

15-2 Mechanisms of Evolution

 Population Genetics and Evolution  Populations, not individuals, evolve!  Genes determine traits of an individual; those who survive and reproduce determine allelic frequency.

Mechanisms of Evolution  The gene pool changes over generations as natural selection affects the allelic frequency.  A population in genetic equilibrium is not evolving…the allelic frequency stays the same.  One mechanism for change is mutation.

Mechanisms of Evolution  Genetic Drift alteration of allelic frequencies by chance events.  Genetic drift can greatly affect small populations  Distinctive species of Galapagos  Amish in Lancaster, PA

Mechanisms of Evolution  Gene Flow when individuals leave or enter a population  Mutation, genetic drift and gene flow can greatly affect a small, isolated population.  Natural selection is usually the most significant factor in causing changes.

Mechanisms of Evolution  Natural Selection acts on variations in 3 ways:  Stabilizing- favors average individuals  Directional- favors one of the extreme variations  Disruptive- selects for either extreme variation  See p. 408 for examples.

Evolution of Species  Define Species  The evolution of a new species is a process called speciation which occurs when members of similar populations no longer interbreed to produce fertile offspring. Speciation of Cichlids

Physical Barriers Prevent Interbreeding  Geographic Isolation  Volcanoes  Continental drift  Mountain formation  Island  Regional varieties due to reduced gene flow & geographic distance

Reproductive Isolation  Conspicuous differences in floral morphology are partly responsible for reproductive isolation between two sympatric species of monkeyflower, due to their effect on visitation of the flowers by different pollinators. (Bumblebees or hummingbirds)  Formerly interbreeding organisms can no longer mate & produce fertile offspring.  Genetic material changes preventing fertilization.  Behavioral ex. Fall vs. summer mating

Change in Chromosome Numbers  Polyploidy results when an individual or species have multiple sets of chromosomes.  Often occurs in plants due to mistakes in mitosis or meiosis or during hybridization.  Polyploid speciation takes only one generation.

Speciation Rates  Gradualism slow, steady rate with small adaptive changes accumulating gradually  Punctuated equilibrium (1972) Eldredge & Gould - speciation occurs rapidly in quick bursts with long periods of equilibrium between

Patterns of Evolution  Adaptive Radiation  Hawaiian honeycreepers  Ancestral species evolved to fit diverse habitats  Occupy own various niche  Divergent Evolution  Similar species diverge becoming increasingly distinct

Patterns of Evolution  Convergent Evolution – unrelated species occupy similar environments in different parts of the world.  Share similar environmental pressures & similar natural selection  See anteaters shown above.  Another example- N. & S. American & African cacti