Anthropology 101: Introduction to Evolution

Theory of Natural Selection

  • What is the Theory of Natural Selection?

    • A mechanism of evolution proposed by Charles Darwin.

    • Suggests that individuals with favorable traits are more likely to survive and reproduce.

    • Traits beneficial for survival are passed on to the next generation.

  • How does Natural Selection work?

    • Variation exists within populations.

    • Some variations offer advantages (e.g., better camouflage, faster movement).

    • Individuals with advantageous traits have higher reproductive success.

    • Over generations, these traits become more common in the population.

  • Does Natural Selection create new variations?

    • No, Natural Selection does not create new variations.

    • It acts on existing variations present in a population.

    • Mutations or genetic recombination are sources of new variations.

  • Limitations to the Theory of Natural Selection as conceived by Darwin:

    • Lack of understanding of heredity and genetics limited his theory.

    • Darwin could not explain how traits were passed down through generations.

    • Ignored environmental and social factors that may affect survival and reproduction.

Explanations for Heredity prior to Genetics

  • Blending Inheritance:

    • The idea that offspring are a blend of parental traits.

    • Traits of parents mix together (e.g., tall + short = medium height offspring).

    • This theory could not explain the stable inheritance of traits across generations.

  • Inheritance of Acquired Characteristics (Lamarckism):

    • Proposed by Jean-Baptiste Lamarck.

    • Suggests that traits acquired during an organism's lifetime can be passed to offspring (e.g., giraffes stretching their necks).

Work of Gregor Mendel

  • Research Construction:

    • Conducted experiments with pea plants to study inheritance patterns.

    • Used controlled cross-breeding and focused on specific traits (e.g., shape, color).

  • Three Principle Conclusions:

    • Dominant/Recessive Traits:

    • Traits can be dominant (expressed in phenotype) or recessive (masked in the presence of a dominant trait).

    • Law of Segregation:

    • During gamete formation, alleles segregate so that each gamete carries one allele for each trait.

    • Law of Independent Assortment:

    • Genes for different traits are inherited independently of each other.

DNA

  • What is DNA?

    • Deoxyribonucleic acid, the molecule that carries genetic information.

    • Composed of nucleotides (adenine, thymine, cytosine, guanine).

  • Location and Construction:

    • Found in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.

    • Constructed as a double helix structure with sugar-phosphate backbones and nitrogenous bases.

  • Replication:

    • DNA replicates by unwinding and separating its strands, with free nucleotides pairing with complementary bases to form two identical DNA molecules.

    • Important for cell division, ensuring genetic continuity in offspring.

Mitosis and Meiosis

  • Mitosis:

    • Process of body cell replication.

    • Produces two identical daughter cells for growth and repair.

  • Meiosis:

    • Process of sex cell replication.

    • Produces four genetically diverse gametes, crucial for sexual reproduction.

  • Importance and Evolutionary Significance:

    • Mitosis is vital for growth; meiosis ensures genetic diversity, which is important for evolution.

Definitions

  • Homozygous vs Heterozygous:

    • Homozygous:

    • An organism with two identical alleles for a trait (e.g., AA or aa).

    • Heterozygous:

    • An organism with two different alleles for a trait (e.g., Aa).

  • Genotype and Phenotype:

    • Genotype:

    • The genetic makeup of an organism regarding a trait.

    • Phenotype:

    • The observable characteristics of an organism resulting from its genotype and environment.

  • Co-dominant Traits:

    • Traits where both alleles are fully expressed in the phenotype of heterozygotes (e.g., AB blood type).

Complex Physical Traits and Evolutionary Forces

  • Pleiotropy:

    • A single gene influences multiple phenotypic traits.

  • Predicting Offspring Distributions:

    • Punnett Squares:

    • A tool used to predict the probability of offspring genotypes from parental genotypes.

  • Sex-Linked Diseases:

    • Disorders associated with genes on sex chromosomes (e.g., hemophilia, color blindness).

Forces of Evolution

  • Forces that Increase Variation:

    • Sexual Recombination:

    • Mixing of parental genes during meiosis.

    • Mutation:

    • Changes in DNA that create new alleles.

    • Gene Flow:

    • Exchange of genes between populations.

    • Genetic Drift:

    • Random changes in allele frequencies, especially in small populations.

  • Forces that Decrease Variation:

    • Natural Selection:

    • Favors certain traits, reducing diversity.

    • Genetic Drift (Founder’s Effect):

    • Decreased genetic variation when a small group starts a new population.

    • Sexual Selection:

    • Preferences for certain traits can lead to reduced genetic diversity within a species.