Evidences of Evolution

Evidences of Evolution

Fossils:

• Formed when animal remains are trapped in sedimentary layers.
• Organic material replaced by minerals over millions of years.
• Result is a "mineral cast" of the dead organism.

Fossilized Trilobite

• Where a fossil is located in the sedimentary strata can indicate it's age.
• Successive changes in fossil forms of an organism can help in developing a fossil record of an organism's evolution.
• Some rare fossils can show "soft tissues" which give invaluable information on an organism's physiology
• Example: paleontologists recently discovered a dinosaur with a fossilized heart. This indicates that this species was most likely warm blooded.

Fossilized Dinosaur Heart

Radiometric Dating:

• Based on the fact that radioactive materials decay at a fixed rate.
• Rate is known as a half-life: The amount of time in which only 1/2 of a radioactive sample remains
• By measuring the amount of radioactive material in a fossil, one can determine how old it is.
• Example is ¹⁴C dating.
• 14C is an isotope of ¹²C which radioactively decays to ¹⁴N.
• It occurs naturally in the environment, and is ingested by organisms while alive.
• Once an organism dies, ¹⁴C intake stops, and the ¹⁴C begins to decay
• One can then measure the amount of ¹⁴C remaining in a sample, and determine its age.

14C Dating

Similarities in Embryological Development

• In early embryological development, it appears that embryos "play out" their evolutionary history.
• Known as Ontonogy recapitulating Phylogeny.
• Implies that genetically, we have not "forgotten" our evolutionary history, only built upon it.

Homologous Structures

• Refers to the fact that organisms' structures are formed from similar anatomy.
• Example the wing of a bird, arm of a man, wing of a bat, and flipper of a whale, all appear to be formed from a common set of bones.
• Implies that these organisms evolved from some common ancestor.

Vestigal Structures:

• Refers to the fact that organisms have structures which are disused
• These structures, however, a remnants of structures the organisms used earlier in their evolutionary history.
• Examples:
• Hip bones in whales
• Tail in humans
• Appendix in humans
• Legs/hips in snakes