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AP Bio Unit 7 Study Guide
Darwin’s Observations:
Each species has the potential to produce more offspring than can survive due to limited resources.
Offspring compete for these resources, leading to a survival struggle.
Variations exist among individuals in every population, affecting their ability to compete.
Evolutionary fitness is assessed by reproductive success; those individuals possessing the most advantageous traits are more likely to survive and reproduce, passing those traits on to future generations.
Fitness can vary due to both biotic (living) and abiotic (non-living) environmental factors, influencing which genetic traits become prevalent over time.
Lamarck and the Long Necks
During Darwin's time, an alternative theory of evolution was advanced by Jean-Baptiste de Lamarck, suggesting that organisms could pass on traits acquired during their lifetimes, a concept that has been largely discredited in favor of Darwinian evolution.
Evidence for Evolution
Paleontology: The study of fossils has unveiled a rich record of evolutionary history. Fossils are dated using techniques such as:
The age of surrounding rocks
The half-life of radioactive isotopes, including carbon-14
Geological layers and location data
Biogeography: Observations of species distributions reveal common ancestry and adaptation to different environments, with related species found in geographically isolated areas.
Embryology: Similarities in embryonic development across vertebrates suggest a common ancestry, evidenced by features such as gill slits in early development.
Morphological Homologies: Comparative anatomy studies reveal homologous structures—similar anatomical features in different species indicating a shared ancestor, as opposed to analogous structures, which evolved independently.
Molecular Biology: Genetic similarities at the molecular level provide some of the strongest evidence for evolution, supporting the idea of shared ancestry among diverse species.
Continuing Evolution
Evolution is an ongoing process, with genetic changes and fossil records consistently showing evidence of adaptation and species change over time.
Common Ancestry
Common ancestry suggests that all forms of life share a lineage. Phylogenetic trees, or cladograms, are graphical representations of evolutionary relationships, constructed using fossil and molecular data to illustrate descent from common ancestors. These diagrams reflect branching patterns of evolution.
Genetic Variability
Variability within a population facilitates natural selection; greater genetic diversity increases the likelihood of advantageous traits appearing in response to environmental pressures. Genetic variation is essential for evolution to occur.
The Peppered Moths
The peppered moth illustrates natural selection. Initially, a balanced ratio of dark and light phenotypes existed. However, industrial pollution led to a predominance of dark-colored moths due to increased survival rates in polluted environments, where lighter moths were more conspicuous to predators.
Causes of Evolution
Natural selection operates under the premise of genetic variation alongside environmental pressures.
Environmental factors—both biotic and abiotic—can guide evolutionary pathways.
Survival of the fittest emphasizes reproductive success; traits enhancing reproduction enhance evolutionary fitness.
Sexual selection may favor traits such as elaborate displays in males, influencing mating choices.
Genetic drift leads to population genetic changes due to random events, independent of natural selection; this includes phenomena like the bottleneck effect and founder effect.
Gene flow occurs when individuals migrate between populations, influencing genetic diversity.
Types of selection include:
Directional selection: favoring one extreme phenotype.
Stabilizing selection: favoring average phenotypes and selecting against extremes.
Disruptive selection: favoring extreme phenotypes at both ends of the spectrum.
Artificial selection: human-influenced selection affecting variation in domesticated species.
Species Population
Speciation requires reproductive isolation, allowing populations to diverge. Different environmental pressures and genetic variations lead to distinct evolutionary paths, resulting in divergent evolution. Rapid changes following stability are termed punctuated equilibrium.
Pre-zygotic barriers inhibit fertilization before it occurs, while post-zygotic barriers prevent hybrid offspring from reproducing successfully.
Convergent evolution occurs when unrelated species develop similar traits due to similar environmental pressures.
Speciation can be categorized into allopatric speciation (separation due to geographic barriers) and sympatric speciation (speciation occurring without physical barriers).
Genetics
Mendelian genetics extends to populations through the Hardy-Weinberg law, which describes allele frequencies in a population under equilibrium:- p² + 2pq + q² = 1 (where p² = frequency of homozygous dominants, 2pq = frequency of heterozygotes, q² = frequency of homozygous recessives).Issues affecting genetic equilibrium include:
Small population size increases vulnerability to random environmental changes.
Mutations introduce new alleles, disrupting genetic equilibrium.
Immigration/emigration alter allele frequencies as species enter or leave populations.
Non-random mating leads to selection of particular traits in partners.
Natural selection favors organisms that are better adapted, enhancing their reproductive success.
Origins of Life on Earth
Scientists Alexander Oparin and J. B. S. Haldane proposed that Earth's early atmosphere was primarily composed of inorganic molecules and rich in gases such as methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O), with negligible free oxygen.The experiments by Stanley Miller and Harold Urey simulated primitive Earth conditions, yielding organic compounds akin to amino acids, reinforcing theories of abiogenesis.The RNA-world hypothesis posits that early life forms may have been basic RNA molecules capable of self-replication.
Key Terms
Natural Selection: A process where organisms better adapted to their environment tend to survive and produce more offspring.
Evolution: The gradual change in the genetic makeup of populations over generations, leading to adaptations that better suit organisms to their environments.
Survival of the Fittest: A phrase often used to summarize natural selection, where the fittest individuals are those who reproduce the most successfully.
Genetic Variation: Differences in DNA among individuals within a population, essential for natural selection to occur.
Speciation: The formation of new and distinct species in the course of evolution, usually as a result of reproductive isolation.
Evolutionary Fitness: The reproductive success of an individual organism compared to others in the population, often measured by the number of offspring.
Common Ancestry: The concept that all life shares a common ancestor, illustrated by phylogenetic trees showing evolutionary relationships.
Directional Selection: A form of natural selection where one extreme phenotype is favored over others.
Stabilizing Selection: A form of natural selection that favors average phenotypes and selects against extremes.
Disruptive Selection: A form of natural selection that favors extreme phenotypes at both ends of the spectrum.
Artificial Selection: Human-influenced selection, where humans determine which traits are favorable for breeding.
Genetic Drift: A change in allele frequencies in a population due to random sampling of organisms, especially in small populations.
Gene Flow: The transfer of genetic material between populations through migration, influencing genetic diversity.
Pre-zygotic Barriers: Reproductive barriers that occur before fertilization, preventing mating or fertilization between species.
Post-zygotic Barriers: Reproductive barriers that occur after fertilization, affecting hybrid viability or fertility.
Convergent Evolution: The independent evolution of similar traits in unrelated species due to similar environmental pressures.
Allopatric Speciation: Speciation that occurs when populations are geographically isolated from each other.
Sympatric Speciation: Speciation that occurs without physical barriers, often through polyploidy or behavioral differences.
Hardy-Weinberg Principle: A principle that describes allele frequencies in a population under equilibrium and provides a baseline for evolutionary change, expressed as p² + 2pq + q² = 1.
Abiogenesis: The study or theory concerning the origin of life from non-living matter.
