Biology Chapter: Darwin's Theory of Evolution

Dog Breeds

• A list of dog breeds is provided, including Affenpinscher, Brussels Griffon, Cavalier King Charles Spaniel, Chihuahua, Chinese Crested, Manchester Terrier, Miniature Pinscher, English Toy Spaniel, Havanese, Italian Greyhound, Japanese Chin, Maltese, Papillon, Pekingese, Pomeranian, Pug, Shih Tzu, Silky Terrier, Toy Fox Terrier, and Toy Poodle, Yorkshire Terrier.

Mechanisms of Evolution

• The mechanisms that produce change in populations from generation to generation are covered, including artificial selection, natural selection, genetic drift, mutation, and recombination.
• Evolutionary thought is traced.
• Specific focus on how common ancestors came to be and how life diversified to its current state.

Ancient Views on Species

• Ancient views held that species were static and unchanging.

18th Century Evolution Ideas

• Georges-Louis Leclerc Comte de Buffon observed that differing geographic regions have similar plant and animal life despite varying environments.
• Extinct species were accepted as a possibility.

Geological Perspectives

• James Hutton proposed that geological change happens gradually through the accumulation of small changes over long periods of time, similar to contemporary processes.
• Hutton's ideas were popularized by Charles Lyell, who became a friend to Darwin.

Charles Lyell's Influence on Darwin

• Lyell's ideas influenced Darwin by proposing a greater age of Earth which provided more time for gradual change in species.
• The gradual change in species was viewed as analogous to gradual changes in species.
• The longer the period/time, the more time for the development of species.

Lamarck's Mechanism for Evolution

• Jean-Baptiste Lamarck detailed a mechanism for evolutionary change in the 19th century.
• Now referred to as the inheritance of acquired characteristics, this mechanism explains that modifications in an organism, due to environment, use, or disuse of structures during its lifetime, are inheritable and drive evolutionary change.

Four Forces or Mechanisms of Evolution

• The four forces or mechanisms of evolution are Natural selection, Mutation, Genetic Drift and Gene Flow (Migration).

Natural Selection

• The actual mechanism of evolution was independently conceived and described by Charles Darwin and Alfred Russell Wallace in the mid-19th century.
• Darwin observed similar, yet distinctly different, species of organisms on different islands.
• Darwin imagined that the island species might be modified from one original mainland species.
• Natural selection is an inevitable outcome of three principles in nature: characteristics inherited from parent to offspring; more offspring than can survive; offspring vary among each other and variations are inherited.
• Darwin's grand idea of evolution by natural selection is described as simple, and is illustrated using a beetle population example:
  • Variation: Beetles have different colors (green and brown).
  • Differential Reproduction: The environment can't support unlimited population growth, so green beetles get eaten by birds, while brown beetles tend to survive longer and reproduce more than green beetles.
  • Heredity: The surviving brown beetles have brown baby beetles since this trait is genetically based.
  • Result: Brown coloration will become more common in the beetle population and eventually the whole population will be brown. -If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome.

Mutation

• Mutation is a change in the DNA sequence of a gene.
• Mutations are a source of new alleles in a population.
• The impact of mutation on evolution is small unless it interacts with other factors like selection.
• Outcomes/effects of mutation on an organism's phenotype:
  • It can affect the phenotype in a way that reduces fitness (lower likelihood of survival, resulting in fewer offspring).
  • It can produce a phenotype with a beneficial effect on fitness.
  • Neutral mutations have no effect on fitness.
• Mutations occur when a DNA gene is damaged or changed in a way that changes the genetic message carried by the gene.
• A mutagen is a substance that results in permanent alteration to the physical composition of a DNA gene so the genetic message is changed.
• Is there a harmful mutation?
• Harmful mutations can cause genetic disorders or cancer.
• Mutation is the ultimate source of genetic variation in all populations - new alleles and therefore new genetic variations arise through mutation.

Genetic Drift

• Genetic drift is a mechanism of evolution referring to random fluctuations in allele frequencies from generation to generation due to chance events.
• Genetic drift can cause traits to be dominant or disappear from a population.
• Effects/impact of genetic drift are pronounced in small populations.
• Genetic drift, also called Genetic sampling error, is a change in gene pool of a small population that occurs strictly by chance.
• Genetic drifts can lead to genetic traits being lost or widespread, ignoring survival or reproductive value of involved alleles.
• Causes of bottleneck effect - volcano eruption, earthquake, overhunting, and radiation poisoning.

Gene Flow

• Gene flow is the exchange of alleles between two or more populations. Also called allele flow or gene migration.
• Animals migrating can carry new alleles from one population to another, and interbreeding with the population leads to gene flow.
• Gene flow tends to increase similarity between remaining populations of the same species because it makes gene pools more similar to each other.

Recombination

• Recombination is a process by which pieces of DNA are broken and recombined.
• Recombination produces new combinations of alleles and creates genetic diversity at the level of genes.
• Recombination is an integral part of the complex process of meiosis in sexually reproducing organisms.
• It results in a crossing over between pairs of genes along a chromosome as revealed in appropriate matings.

Summary

• Factors changing allele frequencies of populations: Natural selection (favoring beneficial traits and behaviors, selecting against deleterious qualities), mutations, and genetic drifting, which is a mechanism of evolution with allele frequency changing.
• The change is due to chance.
• Gene flow tends to lead to populations being more similar.
• Recombination leads to new variation but also places a genetic load.

Seatwork #3

• Why is understanding evolution important?
• Describe the effects of evolution on the diversity of populations.
• Do you think genetic drift would happen more quickly on an island or on the mainland? Why?

Understanding Evolution: Importance

• Understanding evolution is important because it helps solve biological problems that impact our lives such as controlling hereditary diseases.
• Studying the evolutionary histories of disease-causing genes can improve the quality of human life.

Mechanisms and Behavior

• Mechanisms underlying behavior can have evolutionary importance, affecting the probabilities of phenotype emergence. Therefore affecting the likelihood of alternative evolutionary forces.

Evidence of Evolution

• Explain the evidences of evolution (biogeography, fossil record, DNA/protein sequences, homology, and embryology).
• Infer evolutionary relationships among organisms based on evidence of evolution.

Introduction to Evolution

• Darwin's theory of evolution was recognized when verification was supplied, improving on Darwin's ideas with new data from modern scientists.
• Natural selection provides an outline for understanding evolution's ideologies.
• Modern scientists continue collecting data and evidence to confirm and refine current knowledge of evolution.

Activity - Thumbs

• The activity emphasizes the importance of structure in human hands, specifically the thumbs, and its relation to tasks.
• Individuals tape their thumbs to their palms to experience the importance of a structure in humans
• The structure's role in aiding survival.

Evidences of Evolution: Fossils, Embryology, Anatomy, Molecular Biology, Biogeography

• A summary of evidence for evolution, divided into specific categories.
  • Fossils: Fossils are the preserved remnants of ancient organisms (often found in sedimentary rock). They document the existence of now-extinct species that are related to present-day species.
  • Comparative Embryology: Embryology reveals relatedness between widely different organisms. Embryos often show similarities during early development.
  • Comparative Anatomy: Comparing the anatomy and development of organisms reveals a shared "plan" in closely related species, supporting the concept of "descent from a common ancestor".
  • Molecular Biology: Biochemical evidence (similar DNA, ATP, amino acids, and enzymes in various organisms) supports the concept of descent from a common ancestor; similar protein structure suggests shared ancestry. 
  • Biogeography: Observing geographic distributions of species shows common ancestry and adaptation to distinct ways of life in different environments; similar species living in different regions reflect common ancestry and spread. There is a description of the different categories and how they relate to identifying a species.

Test your knowledge on the principles of natural selection and the mechanisms of evolution as proposed by Charles Darwin. This quiz covers key concepts including differential reproduction, mutation effects, and examples of natural selection in action. Perfect for students studying biology or evolution.