Evidence of Evolution-“Descent with Modification” There is evidence for evolution from many fields of science: Earth Anatomy Embryology Genetics Molecular Biology
Tiktaalik Fish with fingers Whale evolution 1. Evidence from the Earth • The Earth is old enough for descent from a “common ancestor” to have occurred. • Fossils have been found of species half way between an ancient species and a modern species (transitional forms). • Examples: fish with flat head and limb-like fins • Whale like creatures losing their limbs
2. Evidence from Anatomy A. Homologous Structures- structures shared by related species and have been inherited from a common ancestor (the ancestor had the structure) • The same structure adapted in different ways, depending on the environment, to produce different species (divergent evolution) • These structures may have different functions.
Coccyx bone Evidence from Anatomy B. Vestigial Structures- homologous structures inherited from ancestors but have lost much or all of their function due to different needs of the descendants Examples: The wings of an ostrich, the pelvis of a whale, the appendix in humans, the coccyx bone (remnant of a tail!).
Evidence from Anatomy C. Analogous Structures- body parts that share common function, but not structure Example: the wing of a bee and the wing of a bird - both are wings (same function) - structure is completely different - both evolved the ability to fly separately (convergent evolution)
Salamander Turtle Human Chicken Fish Rabbit 3. Evidence from Embryology • Early development of the embryo is similar in vertebrates • Embryonic cells in very different organisms develop in the same order to make homologous structures.
4. Evidence from Genetics • Darwin had no idea how heredity worked • We now know that genetic information comes from DNA, mutations cause changes in DNA, crossing over causes variation in offspring, etc. • All living cells use DNA and RNA to direct the production of proteins!! • Suggests that all organisms evolved from a common ancestor with this genetic code
5. Evidence from Molecular Biology • A. Homologous proteins- perform similar functions in very different cells • “Cytochrome C”- a protein that functions in cellular respiration. • Similar versions are found in cells from yeast to humans
Evidence from Molecular Biology • B. Homologous Genes- genes with the same or similar sequences, controlling the same traits, in different organisms • Example:Hox genes- determine the head to tail development of embryos (which end is up) • • Minor changes in these genes produce variations among organisms • • Are present in almost all multicellular organisms (from fruit flies to humans)
Phylogeny • Classification using evolutionary relationships in addition to info provided by Linnaean classification (KPCOFGS) • Shows common ancestors and their descendants • Shows common physical characteristics between organisms • Based on similarities in DNA sequences
Cladograms • Diagrams used to show phylogeny • Show derived characters- traits that appeared in the most recent common ancestor • Each fork in the tree represents a common ancestor branching off into more than one species • Which two species share the most recent common ancestor? • Which organisms are characterized by having 4 limbs? • Which species have more features in common: Birds and rabbits, or crocodiles and ray-finned fish? Bird and croc; or rodent and primate Birds, crocs, rodents, rabbits, primates, amphibians Birds and rabbits