Evolution Part 1 The Evidence

Evolution Outline I. What is evolution? II. Evidence of Evolution A. Evidence from the past (Fossils) B. Evidence from living organisms -Comparative anatomy -Comparative embryology -Comparative biochemistry III. Early Hypotheses Origin of Life A. Spontaneous generation B. Atmosphere of early earth – Stanley Miller experiment C. Heterotroph hypothesis

Evolution Outline (Con’t) IV. Theories of Evolution A. Early Theories 1. Lamarck: Theory of acquired traits “Use and disuse” 2. Darwin and Wallace:Theory of evolution by natural selection B. Synthetic (Modern) Theory of Evolution 1. Population Genetics 2. Genes, Variation and Evolution 3. Hardy-Weinberg Law and Genetic Equilibrium V. Adaptations and Natural Selection A. Structural Adaptations B. Behavioral Adaptations

Evolution Outline (Con’t) VI. Types of Natural Selection A. Directional Selection B. Stabilizing Selection C. Disruptive Selection VII. Speciation and Adaptive Radiation A. Geographic and reproductive isolation B. Convergent evolution C. Coevolution VIII. Classification and Evolutionary Histories A. Phylogenetic trees B. Taxonomy

What is evolution? Evolution is the central and unifying theme in biology. “Nothing in biology makes sense unless cast in the light of evolution” – Theodozius Dobzhonski Evolution is the gradual change in a population of organisms over time. Geologic evolution: Refers to the gradual changes in the Earth over the last 4.5 billion years Organic evolution refers to the changes in life forms as they adapt to their changing environments.

Is evolution real? There is no doubt that evolution has occurred, is occurring, and will continue to occur as organisms constantly adapt to changing environments. Convincing evidence comes from the fossil record. Fossil: any trace or remains of an organism that has been preserved by natural processes.

Transitional Fossils – Evidence of Evolution Part 1 Archeaopteryx: Had teeth and a long tail like a dinosaur, but feathers like a bird. This fossils demonstrates how birds are modern descendents of dinosaours.

Transitional Fossils Tiktaalik: 375 million year old fish whose fins appear to be “limbs in the making” The figure below shows bones in the fins that are homologous to bones that make up the fingers, wrists, and elbows of terrestrial (land dwelling) vertebrates.

Transitional fossils Evolving from life in the sea to life on land required some major limb adjustments Tiktaalik is a long awaited piece of the puzzle of how life transitioned from sea to land

Sealing up “gaps” in the fossil record. Opponents of evolution often point to a “lack of evidence” or “gaps in the fossil record” to justify their position. …but rarely change their positions when confronted with the real evidence.

But surely this evolution stuff doesn’t apply to humans.

Question to Ponder Why aren’t there more, lots more, transitional fossils out there? Most fossils are of organisms in their “complete” state.

Evidence for Evolution Part 2: Comparative Anatomy What traits would you use to classify: -Birds -Mammals -Reptiles -Fish Feathers, lay eggs Fur, milk, live young Scales, cold-blooded, lay eggs Scales, gills, fins

Comparative Anatomy: Homologous Structures Homologous Structures: are characteristics which are shared by related species because they have been inherited in some way from a common ancestor. For example, although the arms of four-limbed vertebrates externally appear quite different, all have the same basic underlying skeletal and muscular pattern. Such shared patterns are best explained by the inference that they were inherited from a common ancestor that also had this pattern.

Homologous Structures and Wing Development The wings of flies, moths and butterflies, and beetles are homologous structure derived from a four winged common ancestor.

There is also homology in gene expression Similarities in gene expression between mammals and insects demonstrate the common ancestry of ALL animals.

Comparative Anatomy: Analogous Structures Would you say that a butterfly is more closely related to a bird or an ant? But birds and butterflies both have wings. True, but the underlying structure of those wings are completely different. Insect wings and bird wings are considered Analogous Structures. Insect wings and bird wings have evolved independently of each other. They illustrate two different evolutionary pathways to the same result – wings. This is called convergent evolution Analogous structures do not demonstrate common ancestry between organisms.

Analogous Structures Here we can see why vertebrate forelimbs are considered HOMOLOGOUS – reflecting the common ancestry of all vertebrates. And why the wings of insects and birds are considered ANALOGOUS – reflecting the convergent evolution of bird and insect wings.

Comparative Anatomy:Vestigial Organs Some of the most compelling evidence supporting evolution comes from vestigial organs. Vestigial organs: Structures that were functional in early ancestors, but are now useless in present day organisms. Ex. Hind-limb bones in whales and snakes, human appendix and nictitating membranes Why does this early whale fossil have non-functional leg bones? They were used by a land dwelling ancestor similar to modern hippos

Vestigial leg bones found in snake fossil This fossil demonstrates the evolution of snakes from lizards. The loss of limbs enables snakes to exploit new areas in search of prey, that would not be accessible to lizards. The only sensible explanation as to why a snake fossil would have functionless leg bones is an evolutionary explanation

Vestigial Eyes in Cave Dwelling Salamanders Grotto salamander Typhlotriton spelaeus This lizard lives in caves with absolutely no light. Rather than invest precious resources for unnecessary eye development, these blind creatures have functionless bulbs of tissue rather than eyes.

Evidence for Evolution Part 3 – Comparative Embryology Comparative embryology: Refers to the similarities and differences between organisms during embryological development. Vertebrate embryos develop in very similar ways.

Evidence for Evolution Part 4: Biochemical Similarities

Comparative Biochemistry Just as DNA can be used to demonstrate paternity, it can also be used to demonstrate common ancestry between species.

We don’t just look like other primates, we share most of our DNA with them too!

Evidence for Evolution Part 6: Artificial Selection Artificial Selection and Selective breeding has enabled humans to develop a variety of dog, horse, livestock, and agricultural breeds. Darwin argues that humans are simply playing the part of the environment in the selection of desired traits. All of these vegetables come from the same mustard plant!

Artificial selection in dogs All dog breeds (Canis familiaris) are derived from domesticated dogs very similar to wolves. Artificial selection gives us tremendous diversity within the species.