Bio 111: Chapter 15

Topics in Evolution Study Guide

Definition of Evolution

• Evolution: The change in the genetic composition of a population over generations, driven by mechanisms like natural selection, genetic drift, gene flow, and mutation.

  • Evolution occurs at the population level (not individuals) and results in adaptations, speciation, or changes in allele frequencies over time.

  • Example: The development of antibiotic resistance in bacteria.

Natural Selection

• Natural Selection: A process where individuals with traits better suited to their environment are more likely to survive, reproduce, and pass on those advantageous traits

• Fossils: Preserved remains, impressions, or traces of organisms from the past found in sedimentary rock.

  • Provide a historical record of life and evidence for evolution.

  • Fossils show transitional forms, such as Archaeopteryx, which bridges the gap between reptiles and birds.

  • Example: Fossilized whale ancestors show the transition from land-dwelling to aquatic mammals.

Darwin, Wallace, Lamarck

1. Charles Darwin

   • Developed the theory of evolution by natural selection in his book On the Origin of Species (1859).

   • Observed variation and adaptation in species like Galápagos finches.

2. Alfred Russel Wallace

   • Independently proposed a similar theory of natural selection based on observations in Southeast Asia and the Amazon.

   • Credited as the co-discoverer of natural selection.

3. Jean-Baptiste Lamarck

   • Proposed the theory of inheritance of acquired characteristics, suggesting that traits developed during an organism’s lifetime could be passed on to offspring.

   • Example (incorrect): Giraffes developed long necks because they stretched to reach higher leaves.

Lines of Evidence for Evolution

1. Fossils

• Fossil records document transitional forms and changes in species over time.

  • Example: Tiktaalik shows the transition from fish to tetrapods.

2. Biogeography

• Study of the geographic distribution of species.

3. Comparative Anatomy

• Comparing structures of different organisms reveals evolutionary relationships.

  • Homologous Structures: Structures shared by related species due to common ancestry but with different functions.

    • Example: Forelimbs of humans, bats, and whales.

  • Divergent Evolution: Evolution of different forms or functions from a common ancestor.

    • Example: Mammalian forelimbs adapted for flying, swimming, or grasping.

  • Vestigial Structures: Structures with reduced or no function, inherited from ancestors.

    • Example: Human appendix, whale pelvic bones.

  • Analogous Structures: Similar structures with the same function but different evolutionary origins.

    • Example: Wings of birds and insects.

  • Convergent Evolution: Evolution of similar adaptations in unrelated species due to similar environmental pressures.

    • Example: Shark and dolphin body shapes.

4. Modern Biochemical and Genetic Analyses

• DNA and protein comparisons reveal evolutionary relationships.

  • Example: Humans share ~98% of their DNA with chimpanzees.

• Molecular Clock: Mutations accumulate at a predictable rate, allowing scientists to estimate divergence times between species.

5. Embryology

• Early developmental stages of different species show similarities, suggesting common ancestry.

  • Example: Vertebrate embryos have pharyngeal slits and tails during early development, even in species that don’t retain them as adults.

6. Artificial Selection

• Humans selectively breed organisms for desired traits, providing a model for natural selection.

  • Example: Domestication of dogs, or breeding crops like corn for higher yield.

7. Natural Selection in Real Time

• Evolution can be observed within human lifetimes due to environmental pressures or selective breeding.

  • Example:

    • Evolution of pesticide resistance in insects.

    • Antibiotic resistance in bacteria (e.g., MRSA).

    • The development of longer beaks in Darwin’s finches during drought years to access scarce food.