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Evolution Notes Honors

Evolution

Definition of Evolution

  • Process by which living things have undergone continuous change since they first appeared on Earth.

  • A central and unifying theme of biology.

Fossil Evidence

A. Definition of Fossil

  • A fossil is the preserved remains or any trace of an organism that lived at some time in the past.

  • The study of fossils provides the first and strongest evidence of evolution.

B. Formation of Fossils

  1. Preservation of Whole Organisms: Found in tar, amber, or ice.

  2. Preservation of Hard Parts: Such as shells or bones.

  3. Petrifaction: Gradual replacement of organic parts by minerals; the organism turns to stone.

  4. Sedimentation: Sediments gradually settle out of water and bury dead organisms that may leave traces.

C. Fossil Sequences

  • Upper layers in sedimentary rock are laid down over lower layers; thus, upper layers are younger than lower layers.

  • Fossils in upper layers are younger than those in lower layers, provided the layers have not been disturbed by geological processes.

Timeline of Early Life

  • The earliest organisms were simple and one-celled, followed by complex one-celled organisms with organelles.

  • Approximately 1 billion years ago, complex multicellular organisms appear in the fossil record.

D. Evolutionary Patterns

  • Sequences in the fossil record indicate that later forms developed from earlier forms through changes passed from generation to generation.

Geological Time Scale

Major Eras and Periods

  • Mesozoic Era: Includes the Triassic, Jurassic, and Cretaceous periods.

  • Cenozoic Era: Includes the Tertiary and Quaternary periods.

  • Paleozoic Era: Features significant events of life's evolution.

Major Evolutionary Events

  • Humans evolved about 24 million years ago.

  • First placental mammals appeared 65 million years ago.

  • Flowering plants dominated the landscape.

Comparing Anatomy

A. Study of Structural Similarities

  • Comparative anatomy shows structural similarities and differences among living organisms.

  • For example, compare forelimbs of humans, whales, cats, bats, and birds.

B. Homologous Structures

  • Similar structure and embryonic development but different forms/functions among organisms suggests evolutionary relationships.

  • Homologous structures evolve similarly; they have the same number of bones arranged similarly.

Comparative Development

A. Embryonic Development

  • Closely related organisms have similar patterns of development, as seen in vertebrate embryos which show similarities such as gill slits, two-chambered hearts, and tails.

  • The more closely related, the longer they resemble each other during development.

B. Comparative Cell Structures

  • Similarities in cell organelles (membrane, ribosomes, mitochondria) across species.

C. Biochemical Comparisons

  • Organisms that are closely related have similar DNA and protein molecules.

The Theory of Evolution

A. Lamarck's Theory

  • Use and Disuse: Body parts used extensively become larger, while unused parts deteriorate.

  • Inheritance of Acquired Characteristics: Modifications can be passed to offspring (e.g., giraffes stretching necks for food).

B. Darwin's Contributions

  • Darwin proposed that evolution occurs through natural selection, similar to artificial selection by breeders.

  • Key observations included slow geological processes, competition for resources, and selective breeding.

Natural Selection

Key Mechanisms

  1. Overproduction: More offspring produced than can survive.

  2. Competition: Competing for food, shelter, and reproductive opportunities.

  3. Variation: Some individuals have better survival traits than others.

  4. Survival of the Fittest: Those best adapted survive and reproduce, passing favorable characteristics to the next generation.

  5. Evolution of New Species: Accumulation of favorable traits can lead to the emergence of new species.

Genetic Variation

A. Sources

  • Genetic shuffling during meiosis and fertilization provides gene combination diversity.

  • Mutations are random changes in DNA and a source of new genes.

B. Importance

  • Genetic variation allows populations to adapt to changing environments and prevents extinction.

  • Adaptations improve survival chances in specific environments.

Natural Selection Observations

A. Examples

  1. Industrial Melanism: Dark-colored moths became common due to pollution.

  2. Bacterial Resistance: Antibiotic resistance evolved in new bacterial strains.

  3. Insect Resistance: Resistance to pesticides observed in insect populations.

Population Genetics

A. Definitions

  • Individuals do not evolve; populations evolve over time.

  • Gene pool represents the total number of alleles present.

B. Hardy-Weinberg Law

  • Gene and genotype frequencies remain constant unless acted upon by outside forces, under certain conditions.

Environmental Changes and Evolution

A. Environmental Impact

  • Unstable environments drive evolution; stable environments result in little change.

B. Isolation and Speciation

  1. Geographic Isolation: Separation by physical barriers.

  2. Reproductive Isolation: Gene pools become so different they can no longer interbreed.

Evolutionary Principles

A. Rate of Evolution

  • Linked to environmental changes; rapid changes occur in response to environmental shifts.

  • Gradualism vs. Punctuated Equilibrium:

    • Gradualism: Slow, continuous changes.

    • Punctuated: Short bursts of change followed by stability.

B. Extinction

  • Extinction happens when species cannot adapt to environmental changes.

Conclusion

  • The fossil record shows millions of species have existed and gone extinct; variation increases survival chances.

  • Extinction examples include dinosaurs, dodo birds, and endangered species like the Bengal tiger.