Evidences of Evolution Read Section 8.2 on pp. 332 – 338 of your textbook

There are 5 key evidences for evolution: Fossil record Biogeography Anatomical evidence (homologous structures, vestigial structures) Embryology DNA evidence

1. Fossil record Fossils are preserved remains or markings left by organisms that lived in the past. Paleontologists (scientists who study fossils) have discovered fossils of many ancestral life forms that link past and present. Fossil evidence supports the hypothesis that whales, which have no hind limbs, evolved from land-dwelling ancestors with four limbs.

2. Fossil record

2. Fossil Record The oldest fossils are called microfossils, and they are the fossilized remains of single celled organisms. They must be viewed under a microscope. Microfossil evidence suggests that life first evolved about 3.5 billion years ago. Microfossils are found in ancient rock structures in South Africa and Australia. The microfossils form structures called stromolites. Stromolites are produced by microbes (mostly photosynthesizing cyanobacteria) that form microbial films that trap mud. Over time, these layers of microbes and mud form “mats” that build up into a layered rock structure.

Stromolites

Fossil record – see p. 334

1. Fossil record Provides the following evidence: Fossils found in younger rock layers (close to surface) are more similar to species alive today that those fossils found in older, deeper layers of rock Fossils appear in chronological order in rock layers. Probable earlier ancestors for a species are found in deeper rock layers, which lie beneath the more recent ancestors. Not all organisms that are alive today have ancestors at all layers of the fossil record. Fossil history suggests that the oldest vertebrates (back-boned animals) are fish. In recent layers of rock, you will find amphibians, reptiles, mammals and birds. Fish  amphibians  reptiles  mammals birds

Transitional fossils These are fossils that fill in gaps in the fossil record. They show i intermediary links between ancient and more recent fossils. Their existence is often predicted to link existing fossils. When found, they help support the theories proposed about how a species evolved. Basilosaurus – fits in between

2. Biogeography The study of the past and present geographical distribution of organisms. It suggests that organisms evolve in one area, then spread out to other regions Geographically close environments (e.g. desert and forest in South America) are more likely to be populated with related species than are locations that are geographically separate but environmentally similar (e.g. desert in Africa, desert in Australia). E.g. cacti are only found in deserts in North, Central and South America, not in deserts in Africa or Australia

2. Biogeography Animals found on islands often closely resemble animals found on the closest continent. E.g. Darwin’s Galapagos finches were more similar to finches found in South America (Ecuador) than to those found in England

3. Anatomical Evidence Vestigial Structures are remnants of structures that may have had important functions in an ancestral species. Vestigial structures are often reduced in size. For example : Hip bones in whales Human appendix

3. Anatomical Evidence Homologous structures - structures that are similar because they were inherited from a common ancestor. These structures may have evolved to have different functions.

3. Anatomical Evidence-Homologous structures All mammals have an almost identical number and arrangement of bones. Bat Human

3. Anatomical Evidence Analogous structures are not considered to be an evidence that supports evolution. An analogous structure is a structure that has a similar function in contemporary species, but has evolved through different pathway. Structurally they are often not similar. Example: bees wings and bird wings

4. Embryological evidence In the development of an embryo, general traits appear before the more specialized traits. Embryos of different species are more alike than the adults, and they change progressively during their embryonic growth to look less and less alike. Vertebrate embryos show many similarities, for which the most reasonable explanation is their common ancestry.

4. Embryological evidence Example: The gill slits in the mammalian embryo are similar to those of a fish embryo at a comparable stage of development. They change into structures quite different from those in the fish. All the gill slits close and disappear except the one that forms the Eustachian tube, which connects the pharynx at the back of the mouth to the middle ear. The obvious question is why should there be a stage in the mammalian embryo where gills are present, even though they form quite different structures in an adult mammal? The answer is that the mammals are descended from fishlike ancestors and that in the course of evolution modifications have occurred in its development.

4. Embryological evidence The similarities which still persist in the embryonic development of fish and mammals indicate a similarity in their genetics due to their common ancestry. Embryos still carry the clues to their common ancestry.

4. Embryology (a type of anatomical evidence)

5. Molecular biology What molecule serves as the blueprint of life? DNA What molecules are encoded for by DNA? PROTEINS How do we compare organisms from a molecular point of view? We can look at the sequences of DNA in their genes or the sequences of amino acids in their proteins

5. Molecular biology Cytochrome c – electron transport chain protein for cellular respiration Similarities in the structure of this protein can be used to demonstrate evolutionary relatedness 20 of 104 amino acids occupy identical positions in all eukaryotic cells (19.2%) Human vs horse cytochrome c – differ in only 12 amino acids (88.5% similar) Human vs kangaroo cytochrome c – differ in only 8 amino acids (92.3% similar) Human vs chimpanzee – identical

5. Molecular biology