Evidence for Evolution SBi3U BioLogy

What lines of Evidence help us understand Evolution? Fossils Anatomy Embryology Biogeography Biochemistry Artificial Selection

The FossiL Record Fossils = mineralized remains of organisms, or their imprints. Form only under very specific conditions!

The FossiL Record Impression fossils form when an organism dies, and before entirely decomposing is covered by silt, mud or ash. The flesh decomposes inside this casing of minerals, leaving a ‘negative imprint’ Parts of the organism may mineralize

The FossiL Record Cast fossils start off similarly, but large, tough structures such as bones remain after decomposition. Over time, minerals seep in, replacing the CaPO4 in the bones. The remains are now petrified, or ‘made of stone’. A fossil is really a rock shaped like an organism.

The FossiL Record Paleontologists can place fossils by their location in specific strata Stratigraphy = study of fossils in strata Deeper strata = older fossils = more unusual organisms Some fossils tend to be found in certain minerals (granite, limestone…) Others can be linked to other species; this is called faunal correlation

The FossiL Record In Darwin’s time, fossils were a new thing Tangible evidence of change over time For some organisms, we have a very complete & continuous fossil record; for example, the horse. Virtually any organism can fossilize, from microbes through plants to animals.

Example: Horses

Example: The Felidae

Example: Elephants

Fossil Problems Fossilization needs a specific set of conditions; if not everything fossilizes, what have we missed? Incomplete or fragmented fossil records: we have some fossils in some strata, then none in several others…what was in the gap? Limited numbers of fossils: only one of a certain type of fossil is found; does it accurately represent the whole species?

Comparative Anatomy Similar body structures indicate similar origins Homologous Organs: similar structure, different use (related!) Analogous organs: same use, different structure. (not related!) Vestigial organs: still present, function lost; i.e. appendix & coccyx in humans; hip bone in whales.

Homologous Organs

Analogous Organs homologous analogous

Vestigial Organs

Plesiomorphies & Synapomorphies

Embryology Vertebrate embryos all start out very similar, then diverge in form The longer the similarity lasts, the more closely related two organisms are. In Darwin’s time, they thought embryonic development was a ‘mini-evolution’ of sorts ‘Ontogeny recapitulates Phylogeny’ = Embryo development imitates species evolution

Embryology Ernst Haeckel, 1874

Biogeography Similar environments cause similar selective pressures on species A selective pressure is any biotic or abiotic factor that influences your survival. Similar selective pressures direct evolutionary change toward similar adaptations Parallel evolution Convergence

Biogeography All antelopes, all grassland dwellers… Africa Europe North America Asia - India All antelopes, all grassland dwellers… Asia - Tibet

Biochemistry Darwin didn’t have this technology…too bad! DNA analysis: Humans & Chimpanzees are 98% similar Hemoglobin analysis: Human & chimp Hb is identical; human & horse is 80% similar Cytochrome proteins in the mitochondrion… Histone proteins in the cell nucleus…

Biochemistry: Comparing DNA

Biochemistry: Cytochromes

Biochemistry: Hemoglobin

Artificial Selection Darwin was a pigeon breeder, so he knew this well! Domestication: Humans have changed many species by selective breeding. Demonstrates the possibility for change in much shorter time Sometimes, the traits we select are not the ones nature would!

Example: Corn

Example: Cows & Dogs