Evolution and Evidence

Biogeography

  • Biogeography examines the distribution of organisms and their ancestors.

  • It's comprised of "bio" (living things) and "geography" (location).

  • It focuses on where organisms live currently in relation to where their ancestors lived.

Closely Related Organisms

  • Closely related organisms may exhibit some differences.

  • Darwin observed local variations in species, such as finches on the Galapagos Islands with different beaks adapted to different food sources.

  • Differentiation occurs due to slight climate changes in localized areas, influencing necessary structures.

Distantly Related Organisms

  • Distantly related organisms may appear somewhat similar.

  • Darwin noted that species varied globally.

  • Species develop similarities based on similar environments, even on different continents.

  • Example: The armadillo, the aardvark, the pangolin and the glyptodon.

  • Similar traits include long snouts, body shape, and tails.

  • Organisms evolve similar characteristics due to environmental influences.

Age of Earth and Fossils

  • Fossils support the concept of evolution.

  • Fossils in Darwin's time were difficult to date precisely.

  • Modern technology, such as radioactive dating, accurately determines the age of rocks and fossils.

Radioactive Dating

  • Living organisms absorb radioactive carbon-14 (C^{14}) during their lifetime.

  • Upon fossilization, C^{14} decays.

  • Scientists burn a piece of the fossil to produce carbon dioxide gas.

  • The gas emits stable carbon-12 (C^{12}) and radioactive carbon-14 (C^{14}).

  • By measuring the decay rate of C^{14}, the age of the fossil can be estimated.

Fossil Discoveries

  • More fossils have been discovered since Darwin's time, filling in gaps in the fossil record.

  • Intermediate stage fossils show gradual development of species.

  • Example: The gradual development of limbs from fish to amphibians, reptiles, birds, and mammals.

Anatomy and Embryology

  • Comparison of anatomy and embryology provides evidence for evolution.

  • Anatomy involves studying homologous structures.

Homologous Structures

  • Homologous structures: animals with similar structures evolved from a common ancestor.

  • This is referred to as descent with modification.

  • Examples: the frog, alligator, chicken, horse, and ancient lobe-finned fish.

  • Lobe-finned fish are considered common ancestors.

  • These structures have been modified over time but share a common origin.

  • The similar bone structures are color-coded to indicate homology.

Analogous Structures

  • Common structure should not be confused with common function.

  • Analogous Structures: Structures with similar functions but different underlying anatomy (e.g., bat wing, bird wing, insect wing).

  • These are not homologous as the structural components differ.

Vestigial Structures

  • Not all homologous structures have important functions; some are vestigial.

  • Vestigial structures are inherited but have lost most or all of their original function.

  • Examples: ear muscles, eyebrow, eyelashes, tonsils, thymus gland, and male nipples.

Embryology

  • Embryos of different animals (rabbit, calf, hog, chick, tortoise, salamander, fish) appear very similar in early development.

  • Similarities diminish as development progresses, but some remain.

  • By full term, organisms become very different.

  • The similar pattern of embryological development provides evidence of a common ancestor.

Genetics and Molecular Biology

  • Life has a common genetic code (DNA and RNA).

  • DNA and RNA carry information from one generation to the next and direct protein synthesis.

Genetic Code Comparison

  • Compare the genetic code (A, T, G, C) among different organisms (mouse, whale, chicken).

  • Fewer differences indicate closer relationships.

  • Example: Mouse and whale have fewer differences than mouse and chicken, indicating they are more closely related.