EVIDENCE OF EVOLUTION

I. THE FOSSIL RECORD & TRANSITIONAL SPECIES Importance Provides the best proof of the history of life showing how extinct species have lead to today’s species “Lucy”, 3.2 MY Archaeopteryx, 150 MY

Completeness of the Fossil Record?

Transitional Species (Common Ancestors) Location where two species evolutionary path connect on the “tree of life” Scientists search for common ancestors in the fossil record to show the evolutionary connection between species & how they change over time.

Transitional Species Example – Whale Evolution

Transitional Species Example – Whale Evolution Whales and dolphins link to land goes back to Pakicetus, a hoofed mammal. The proof lies in their ears (intermediate between terrestrial and fully aquatic mammals) and its triangular, whale-like teeth. They were possibly fish eating scavengers that ventured into the water to find live prey. Ambulocetus which had webbed toes making it adapted for swimming. Its fossilized bones suggest it undulated its spine vertically in the water like dolphins and whales of today (not side-to-side like fish). Basilosaurus had tiny, weak hind “legs” left over from its evolutionary past. It had sturdy front flippers most likely making it fully aquatic and also swam like modern whales and dolphins.

Transitional Species Examples Complete the Transitional Species & Fossil Record Stations

II. Comparative Anatomy Homologous Structures Analogous Structures Vestigial Structures

Homologous and Analogous Structures Sometimes people look like one another for different reasons. Two sisters, for example, might look alike because they both inherited brown eyes and black hair from their father. While two people attending an Elvis impersonators’ convention may look alike because they are both wearing rhinestone studded suits and long sideburns. The similarity between the sisters is inherited, but the similarity between the Elvis impersonators is not. It works the same way in biology. Some structures are similar among species because they were inherited from a common ancestor (homologous). While some structures are similar in unrelated species because they adapted to similar environmental conditions (analogous).

Homologous Structures traits inherited by two different organisms from a common ancestor that have the same structures, but have adapted different functions. Homologous structures support the idea of a shared common ancestor EX: vertebrate forelimb bones

Analogous Structures Unrelated species with structures that may look and function similarly but are made up of parts that do not share a common evolutionary path showing no connection to a common ancestor. These similarities usually exist because the unrelated species are adapting to similar environmental conditions. EX: wings for flight and fins for swimming

Which limbs are Homologous and which are Analogous in each set? Why? Human Lizard Octopus B Bird Whale Grasshopper Lizard Human

Homologous structures are inherited from common ancestors Homologous structures are inherited from common ancestors. The octopus limb could only be homologous to the lizard limb if they both inherited the limb from a common ancestor. This family tree shows how the octopus is related to vertebrate limbs. Vertebrate limbs and octopus limbs evolved independently after their point of common ancestry, so they were not inherited from a common ancestor. Therefore, they are considered analogous. The same is true of the grasshopper leg.

Can Genes be Homologous?

Vestigial Structures structures that are found in an organism but appear to serve no function (reduced in size) they are remnants of an organism’s evolutionary past Ex: Whales and snakes have pelvic bones; manatees “sea cows” have finger nails on their fins Humans? ear muscles canine teeth Goose bumps appendix Tail bone Wisdom teeth

III. Comparative Embryology similarities in the developmental pattern of organisms exist because of a common ancestor vestigial gill slits/pouches bony tail covered in a fine hair Two chambered hearts Which is a chicken, pig and human? Human embryo Pig embryo Chicken embryo

Comparative Embryology in Vertebrates All vertebrates are similar in early stages of development. Differences accumulate as development continues. New development instructions are added to old instructions inherited from ancestors.

Comparative Embryology in Vertebrates All vertebrates are similar in early stages of development. Differences accumulate as development continues. New development instructions are added to old instructions inherited from ancestors.

Human Embryology

IV. Comparing Genetics An organism’s evolutionary history is held in their DNA sequence (genetic code) If a species changes, their DNA changes Genetic testing compares the similarity of DNA between organisms The more closely related the species are to each other the more similarities they share in their DNA Ex. Chimpanzees & Humans have over 98% the same DNA

What is DNA?

Cytochrome c Cytochrome c is a protein organisms need for respiration. Proteins are made of an amino acid sequence that is determined from our DNA sequence. So if the amino acids in the cytochrome c protein is slightly different between species it also means their DNA is slightly different. Virtually every organism uses cytochrome c; however, each species’ cytochrome c differs slightly from other species. The differences among cytochhrome c exist in the amino acid sequence which were produced by mutations in the species DNA. These mutations occurred after the ancestors of the living species diverged. Therefore, if two species shared common ancestors until fairly recently, their DNA and proteins are likely to be more similar.