Evidence of Evolution • There is a gigantic body of evidence supporting evolution. • Six major areas of study contribute to that body of evidence:
1. The Fossil Record 2. Comparative Anatomy 3. Comparative Biochemistry 4. Molecular Biology 5. Comparative Embryology 6. Biogeography 1. The Fossil Record • Fossils: remains or traces of organisms that once lived, often found in sedimentary rock, ice, tar, or amber.
• The fossil record is the history of life as documented by fossils. • The fossil record shows change over time: • The oldest fossils are prokaryotes • Prokaryotes were probably the first organisms on earth. • Simple organisms Æ More complex organisms • Life began in the sea before moving onto land • Over 99% of the species that once lived on Earth are now extinct.
The Fossil Record (con’t)
• The Earth is about 4.6 billion years old, according to radioactive dating.
• Radioactive/radiometric dating: a technique used to date the age of rocks based on the amount of radioactive isotopes in a rock sample and the half‐ lives of the isotopes.
• Half‐Life: the amount of time it takes for a radioactive element to decay to half its mass.
Carbon‐14 Dating • Carbon‐14 Dating is a commonly used form of radioactive dating. • Uses the isotope Carbon‐14, which decays into Carbon‐12. • The ratio of Carbon‐14 to Carbon‐12, along with the half‐life of Carbon‐14, can tell us how old a sample is. 300 millions years old (according to radiometric dating) Transitional Fossils: link extinct species to modern species.
• Archaeopteryx is a fossil taxon that links ancient reptiles to modern birds.
Hyracotherium (Eohippus) is an ancestor of the modern horse (Equus). “Selfie” 2. Comparative Anatomy
• Comparing the anatomical structures of different organisms can help us determine how closely related different species are.
Chimps, humans, and A. afarensis are all closely related. We share a common ancestor who lived less than 10 million years ago. Comparative Anatomy (con’t)
Homologous Structures: share a common structure, but have different functions.
Homologous structures are evidence of common ancestry (relatedness).
Humans, Cats, Whales, and Bats are all mammals. They diverged from a common ancestor hundreds of millions of years ago. Comparative Anatomy (con’t) Analogous Structures: share a common function, but have different structures.
Analogous structures are NOT indicators of common ancestry.
Insects, birds, and bats are very distantly related. Wings evolved independently several times because they are so useful! Comparative Anatomy (con’t) Vestigial Structures: structures that have no current function.
• Vestigial structures are inherited from ancestors that did use the structure. • Evidence that the anatomy of animals has evolved.
• Examples: Appendix, Wisdom Teeth, Coccyx (Tail Bone)
https://www.youtube.com/watch?v=OAfw3ak pRe8 Whales have a pelvis and femur! Snakes have hind limbs!
Snakes and whales both evolved from populations that once had legs. 3. Comparative Biochemistry • All living things use DNA as their genetic material. • All living things synthesize, transcribe, and translate DNA in the same way. • All living things use enzymes that function identically and have similarly structured cells. Comparing nucleotide sequences in DNA can reveal how closely related different species are. Comparative Biochemistry (con’t) • Because humans and mice are both mammals, they have extremely similar biochemistry. This is why medical researchers can use mice to test medicine for humans. 4. Molecular Biology • Comparing amino acid sequences can reveal how closely related different species are.
Cytochrome c is a polypeptide found in all aerobic organisms. It is necessary for the ETC. 5. Comparative Embryology • Closely related organisms go through similar stages in their embryonic development because they evolved from a common ancestor. • All vertebrates go through a stage where they develop gill pouches. • In fish: gill pouches Æ gills • In humans: gill pouches Æ connection between ears and throat. 6. Biogeography Theory of Continental Drift: 250 mya, all continents were once connected as a supercontinent called Pangaea.
The location of fossils has confirmed theories about the evolution of different organisms. • Examples: Marsupials found on only S. America and Australia. • According to the theory of evolution, the two marsupial populations need to have started in the same place.