Evidence of Evolution (Don’t panic about the length! Out of the 27 slides, only 9 have written info on them. There’s just a lot of pictures.)

Evidence for Evolution There is a wealth of evidence for the theory of evolution, which includes: Fossil record Biogeography Comparative anatomy Comparative embryology Comparative biochemistry Universal genetic code

1. The Fossil Record Fossil- the preserved remains of dead organisms Fossil record- refers to the ordered array in which fossils appear within the strata of sedimentary rock Relative dating- Strata are used to tell the relative age of fossils within each layer Oldest fossils are the farthest down (The following footnotes are just interesting facts. You are not responsible for them.) -Many fossils are not actual remains of organisms, but rocks that are replicas of the organisms (molds, casts, traces, etc). Fossils are sometimes actually turned to stone by petrification. Petrification occurs when minerals that were dissolved in groundwater seep into the tissues of dead organisms. Over time, the organic matter of the organisms gets replaced by minerals. Some fossils can be preserved completely when the are found in resin, bogs, or ice.

The Fossil Record cont. The fossil record shows that organisms have evolved in a historical sequence. It also shows that ancient extinct species are linked to modern species. Transitional fossils- fossils that specifically show the gradual transition from ancient species to modern ones The oldest known fossils are prokaryote cells (3.5 billion yrs) The oldest eukaryotic fossils are a billion years younger. Multi-cellular fossils are even more recent. Fishlike fossils are the oldest vertebrates in the fossil record, followed by amphibians, reptiles, mammals and birds.

Transitional species Pakicetus (terrestrial) Scientists have found these transitional species (ones that specifically show the gradual transition from ancient species to modern ones). This slide shows the evolution of whales from a terrestrial species. This explains why whales have pelvic bones. Rhodocetus (predominantly aquatic) Dorudon (fully aquatic) Balaena (recent whale ancestor)

2006 Fossil Discovery of Early Tetrapod Missing link from sea to land animals

Dickinsonia costata

A Skull of Homo erectus

Ammonite (shelled marine organism) 375 million year old

D Fossilized organic matter of a leaf

E Insect in amber

F “Ice Man”

2. Biogeography Biogeography- the geographic distribution of species Suggested to Darwin that the organisms evolve from common ancestor Ex: Galapagos finches Resembled mainland species more closely than they resembled finches on similar but distant islands

Biogeography cont…

3. Comparative Anatomy Anatomy- studies the structure of the body Comparative anatomy- compares the body structures in different species Anatomical similarities indicate descent from a common ancestor Shows that evolution is remodeling process where ancestral structures became modified as they take on new functions (descent with modification) For example, take the human spine or knee joint. These were derived from ancestral structures that supported four-legged mammals. Many people develop back or knee problems as they get older. If the knee and spine joints were specifically designed for our bipedal posture, we would expect them to be less subject to painful ailments as age.

Comparative Anatomy cont… Homologous structures- structures that are anatomically very similar, but have different functions Analogous structures- Similar structure but no shared evolutionary origin Vestigial structures- Structures that are no longer used Ex: Human tailbone, hind-leg and foot bones in whales, pelvis in snakes

Homologous structures

These homologous structures have the same number of bones that are simply rearranged and modified to suit the organism’s needs.

Analogous Structure These structures underwent the same selection pressure (i.e. they are all built specifically for flight) but the structures differ. They might be similar, but not similar enough to warrant a common ancestor.

Vestigial Structures

Vestigial Structure

4. Comparative Embryology Comparative embryology- the comparison of the early stages of development before birth (embryos) Organisms share certain structures in different embryonic stages Ex: Vertebrates all have pharyngeal pouches at some point in development Similarities in embryonic development indicate that organisms all evolved from a common ancestor.

Chick vs. Human Pharyngeal pouches Post-anal tail Human embryo Almost all vertebrates have an embryonic stage where they have pharyngeal pouches (pouches on the sides of the throat). This indicates that all vertebrates are descended from a common ancestor. The embryos eventually become more distinctive as development progresses. Human embryo Chick embryo

(Hopefully this animation works) (Hopefully this animation works). At the earliest stages of development, all the embryos look very similar. As time goes, they begin to differ. The longer that two organisms remain looking similar, the more closely related they are.

5. Comparative Biochemistry Biochemistry- the study of chemical processes within living organisms Similar amino acid sequences and nucleic acids indicate relatedness The more closely matched the gene sequence, the more likely the organisms evolved from a common ancestor Ex: Comparison of hemoglobin

Biochemistry cont… The greater number of differences in amino acid sequence, the less likely it is that the organisms share a common ancestor. Which organism are most closely related to? Which organisms are we least closely related to?

6. Universal Genetic Code All forms of life use DNA and RNA The genetic is essentially universal Supports Darwin’s theory that all life forms are distantly related.