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.