2 Evidence of EvolutionDarwin argued that living things have been evolving on Earth for millions of years.Evidence supporting his theory could be found:1. Fossil recordGeographical distribution of living speciesAnatomy4. Similarity in early development (embryology)
3 1. The Fossil RecordDarwin saw fossils as a record of the history of life on Earth.Darwin proposed:Earth was millions, rather than thousands, of years oldCountless species had come into being, lived for a time, and then vanished.
4 2. Geographic distribution of Living Species Species now living on different continents had each descended from different ancestors.Some animals on each continent were living under similar ecological conditions so they were exposed to similar pressures of natural selection.
5 Similar, But Unrelated Species As a result, Darwin concluded that because of these similar selection pressures, different animals ended up evolving certain features in common!
6 3. AnatomyDarwin noticed similarities among the body parts of various animal and plants.There are three different types of structures to help support Darwin's Theory of Evolution.Homologous StructuresAnalogous StructuresVestigial Structures
7 Homologous Structures Structures that are similar and have originated from a common ancestor.May look different on the outside, but have similar structure inside.Indicates that organisms may have shared a recent common ancestor.
8 Homologous Structures cont’d. The limbs of different organisms serve different functions, but have the same bone structure inside.
9 Analogous Structures Analogous Structures Structures that serve identical functions, but have different internal anatomy.Ex: wings of birds and insectsBoth allow organisms to fly, but have different development and structure.Shows a more distant relationship than homologous structures.
11 Identify the following structures as analogy or homologous Identify the following structures as analogy or homologous. Be able to defend your answer!
12 Vestigial StructuresVestigial – structures that were useful in ancestors but are no longer used by modern organismsShows relationship between organisms with vestigial structure and those with a working version.Ex: humans have tailbones homologous to tails of other animals
13 Vestigial Structures cont’d. Some organisms have genes that are conserved.Genes that have remained unchanged, but may be “turned off”.Ex: whales have genes for hind legsCan give clues about early development of a species.Ex: whales may have descended from an ancestor who lived on land
14 4. Embryology Embryology – study of early development Many organisms share similarities within the early stages of development.The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.These common cells and tissues, growing in similar ways to produce the homologous structures!Can indicate a common ancestry among different species.
16 Similarities in Macromolecules Similarities within DNA, RNA and proteins of different speciesGenetic code is universal – all living things share the same codeClosely related species have very similar gene sequences and protein sequences.Ex: hemoglobin in humans and gorillas differs by only 1 amino acidCan confirm ideas suggested by anatomy and embryology.