Evidence Supporting Darwin 1) Fossil records 2) Anatomy 3) DNA 4) Embryology
1) Fossils Footprints of dead organisms Tracks Insects trapped in tree sap Impressions of skin Traces of dead organisms.
Conditions to create fossils Must be buried by sediments Swamps, mud, tar pits, ocean bottoms Hard stuff most likely to be fossilized.
How are Fossils Dated? Scientists determine the age of fossils by measuring the amounts of radioactive decay. Half-life describes how long it takes for one- half of the radioactive atoms in a sample to decay. The rate of radioactive decay is constant Scientists can use the amount of radioactive element remaining in a rock or fossil to determine its age. This technique is
2) Anatomy Transitional Species – Evolutionary transitions/ intermediate forms of the organism. Whales- – Are descendants of 4 legged land animals that are also ancestors of horses and cows.
35 mya 42 mya 50 mya 60 mya
Whales- Vestigial Structures -Remnants of an organisms Hind limbs evolutionary past. became smaller Eventually lost Modern whales have a pelvis but, no rear limbs.
Structural Evidence cont. Vestigial Structures: Remnants of an organisms evolutionary past. Structures reduce in size and have no present function.
Structural Evidence Comparing the way two organisms are put together. Homologous structures: Modified versions of the same structure. Similar in structure differ in functions.
3) DNA Evidence Structural, fossils, and developmental evidence still posed many questions. DNA evidence supports the other three. If species change over time, their DNA will also change. Similar organisms = similar DNA Genes accumulate more alterations in their nucleotide sequence over time.
DNA Evidence con’t Compare: chimp, dog, rattlesnake, human Protein- look at amino acid sequence. When comparing a.a. sequences chimps vs. humans 0 a.a. differences – Dog vs human 13 a.a. differences – Rattlesnake vs. human 20 a.a. difference
4) Embryology Early stages of development are similar between organisms.