Evidence for Evolution (College Board AP® Biology): Study Guide

Evidence for evolution

• The theory of evolution by natural selection is now widely accepted by the scientific community due to its being supported by a great deal of evidence

Data that provides evidence for evolution

• Geological evidence examines fossil distribution and rock strata to trace organism changes over time

• Geographical evidence links organism distribution to shared ancestry

  • E.g. finches in the Galápagos Islands and honeycreepers in the Hawaiian Islands demonstrate adaptive radiation

• Physical evidence includes fossils and homologous structures

  • E.g. transitional fossils like Archaeopteryx, a bird-like dinosaur fossil which provides a bridge between dinosaurs and current-day birds

• Biochemical evidence uses DNA and protein sequence comparisons

  • E.g. cytochrome c sequence similarities across species indicate common ancestry

• Mathematical models calculate divergence times and genetic similarity

  • E.g. molecular clocks measure mutation rates in genes to estimate divergence

    • The greater the number of differences there are between nucleotide sequences, the longer ago the common ancestor of both species existed

Evidence of changes in organisms over time

Fossil dating methods

• The age of fossils can be determined using radioactive isotopes to date the fossils or by studying the age of the layers where the fossils are found

  • E.g. naturally occurring carbon-14 in an organism decays at a known rate, based on the half-life of the carbon 14 isotope

  • Scientists measure the level of carbon-14 in fossilized organisms to estimate how long ago that organism died

• Geographical data considers the physical location of species and fossil distribution which allows scientists to establish where common ancestors link different species together

• A combination of fossil dating and geographical data can be used to build timelines of evolution

Morphological homologies

• Homologous structures are similar structures which have different functionalities despite common ancestry

  • E.g. the pentadactyl limb shows structural similarity as well as adaptation

• Vestigial structures, e.g. pelvic bones in whales and wings in flightless bird, suggest evolutionary leftovers from common ancestors

Molecular and cellular evidence

• Similarities in DNA nucleotide sequences, e.g. Hox genes, and protein amino acid sequences, e.g.hemoglobin, show evolutionary relationships between different species

• Higher sequence similarity indicates a closer relationship between species and a more recent divergence from a common ancestor

• Conserved processes

  • Similarities in cellular processes e.g. DNA replication, cellular respiration, and protein synthesis highlight shared ancestry

• Structural evidence

  • Common uses of structural cell components suggest evolutionary links

    • Ribosomes in all cells perform protein synthesis

    • Shared genetic codes and membrane structures (e.g. phospholipid bilayers) indicate a common origin

Evidence for common ancestry

Eukaryotic ancestry

• Structural evidence indicates common ancestry of all eukaryotes:

  • Membrane-bound organelles (e.g., nucleus, mitochondria, chloroplasts) indicate a shared origin in eukaryotic organisms

  • Linear chromosomes in eukaryotes contrast with circular DNA in prokaryotes

  • The presence of introns in eukaryotic genes supports a common eukaryotic lineage

    • E.g., endosymbiotic theory explains how mitochondria and chloroplasts originated from prokaryotes

Continuing evolution

• Life continues to evolve indefinitely driven by changing environments

• There are many observations in the modern day which demonstrate this continual evolution, e.g.:

  • genomic changes

    • Mutations and genetic drift drive divergence over time where greater differences between organisms indicate a more distant common ancestor

  • fossil records

    • Evidence from fossils shows continuous change in traits over time

  • resistance development

    • Mutations are acquired which provide a survival advantage, demonstrating natural selection in action.

    • Evolution of antibiotic-resistant bacteria like MRSA demonstrates natural selection in action

    • Plants and animals evolve resistance to pesticides, e.g. DDT, or herbicides

    • Cancer cells show an increasing resistance to chemotherapy drugs

  • emerging pathogens

    • Seasonal flu variations evolve every year through mutations which alter antigens and cause current vaccinations to become ineffective

    • Diseases like COVID-19 show rapid evolution of pathogens due to environmental pressures