(3) Unit 7 Topics 6 7 and 8 Packet

Evidence for Evolution

• The theory of evolution is supported by various forms of evidence, including:

  • Fossil Record: Documents the history of life through the remains or traces of past organisms.

  • Comparative Morphology: Compares anatomical structures between species.

  • Biogeography: Studies the geographical distribution and comparison of species across different regions.

Fossil Record

• Fossils are remnants or traces of organisms from the past, providing visual evidence of evolutionary changes over time.

• Fossils can be dated using carbon-14, a radioactive isotope with a known half-life, allowing for precise age determination.

• The fossil record provides geographical data, revealing habitats of past organisms.

  • Example: Fossils found in the Grand Canyon offer insights into ancient ecosystems, dating back hundreds of millions of years.

• Limitations of the Fossil Record:

  • It is incomplete, resembling a puzzle with many missing pieces, which prevents a comprehensive view of life’s history.

Comparative Morphology

• Definition: Analysis of anatomical structures between living and extinct organisms.

• Homology: Refers to similarities in characteristics due to shared ancestry, with various types including:

  • Embryonic Homology: Similar embryonic development among species varies, revealing underlying connections.

  • Vestigial Structures: Traits that were once useful but no longer serve a significant function (e.g., human tailbone, appendix).

  • Molecular Homology: Similar DNA and amino acid sequences across species signify shared ancestry, useful for constructing phylogenetic trees.

Homologous Structures

• Definition: Physical characteristics that are similar in different species due to shared ancestry.

• Examples: Arm bones of humans, frogs, lizards, cats, whales, and bats all show significant structural similarities (humerus, ulna, radius, etc.).

• Convergent Evolution vs. Analogous Structures:

  • Convergent Evolution: Similar adaptations in unrelated lineages due to similar environmental pressures.

  • Analogous Structures: Features that are similar but evolved independently in distinct evolutionary paths (e.g., wings of birds, bats, and insects).

Common Ancestry in Eukaryotes

• Evidence supports that all eukaryotes share common ancestry due to fundamental similarities across cellular features:

  • Presence of membrane-bound organelles, linear chromosomes, and introns.

Biogeography

• Definition: The study of the geographic distribution of plants and animals.

• Key Observations:

  • Species on isolated oceanic islands often resemble those from mainland areas.

  • Distinct species exist on the same continent, indicating evolutionary divergences influenced by geography.

Review and Summary

• Data Evidence for Evolution: Fossil data, biogeography, and morphology all contribute substantial evidence.

• Vestigial Structures and Natural Selection: Structures may become vestigial if they were once useful but mutations rendered them neutral, leading to conservation over generations without selection pressures.

• Ongoing Evolution: Populations continue to evolve as genomes change, evident in examples like:

  • Antibiotic Resistance: Especially notable in bacteria due to rapid generation times.

  • Insect Resistance to Pesticides: Seen in cases such as DDT resistance.

  • Emerging Pathogens: New diseases arising demonstrate continuous genomic evolution.

Next Topic

• Upcoming discussion will focus on phylogeny in the next lesson.