Evolution

1. Evolution

2. Evolution: A summary • Evolution - The process of change • Evolution applies to the universe also. Matter and the nature of matter has changed over time • Evolution applies to life, implies that life is not static, but responds to the environment. • Previous western thought held the universe, earth animals, and man were created by a greater being/entity. • Held the earth and life were created in the thousands of years in the past.. • Life and the earth were thought to be static and unchanging. • Modern evolution holds that the universe is billions of years old (between 9-12b years) • Earth was created approx 4.5b years ago. • Human existence is only a small fraction of time since the beginnings of the universe.

3. The Cosmic Calendar • If the 12 billion year history of the universe was fit into a calendar year, it would look like this…..

4. Cosmic Calendar (From The Dragons of Eden - Carl Sagan) Pre-December Dates

5. December DECEMBER December 31

6. December 31

7. Darwin & Natural Selection • Modern evolutionary thought arose through the inquiries of Charles Darwin. • Darwin was a Naturalist aboard an exploration ship called the HMS Beagle. • Collected and catalogued biological specimens for return to England.

8. The Voyage of the Beagle

9. The Galapagos Finches Was fascinated by the species of Finches he observed in the Galopagos Islands. Found that these birds were quite similar to a species found on mainland South America. However they differed significantly in the shapes of their beaks. Darwin reasoned that these species of finches arose from a common ancestor, and gradually changed over to accommodate their particular diets. Led him to develop his theory of evolution through Natural Selection

10. Darwin & Evolution • The notion of evolution was dominated by 2 theories. • Lamarckian Theory of Inheretance of acquired characteristics • Held that traits acquired throughout life of an organism would be passed on to offspring. • "Use it, or lose it principle" • Eg. If you lifted weights during your life, your children would be stronger or, if you did'nt exercise your children would be weaker • Theory has been replaced by Darwin's theory of natural selection. • Natural selection: • Based on following premises: • There are not enough resources for all organisms to survive. • Some organisms are more "fit" to survive. • Fitness refers to: • The ability of an organism to survive in its environment. • The ability of an organism to survive long enough to reproduce. • Natural pressures "weed-out" those individuals "less fit" to survive. Thus changing a species over time. • New genes/traits arise from random mutations. • Most are either Neutral (no effect), or disadvantageous (decrease an organism's chance for survival).

11. Natural Selection : The Peppered Moth: • The peppered moth is a species of moth which uses camouflage against tree bark to avoid being eaten by birds. It is normally a light grey color. • During England's industrial revolution, pollution caused a darkening of the bark of the trees. • There was a natural variation in moth coloration with some being darker than others. • Those moths of a lighter color, were easier to spot and eat by birds. And were eaten at a faster rate. • The survivors tended to be darker, and when they mated, their offspring tended thus to be darker also. • Over time, this resulted in the species becoming darker in color.

12. Lamarck vs. Darwin

13. Effects of Natural Selection • Natural selection can have many different effects on species phenotypes. • These types of natural selection have been named as: • Directional selection • Stabilizing selection • Disruptive selection

14. Directional Selection: • Eliminates one extreme variation from an array of possible phenotypes. Results in a shift towards the other extreme.

15. Stabilizing Selection: • Selection acts to eliminate both extremes of an array of phenotypes. Results in an increase in individuals exhibiting an intermediate phenotype.

16. Disruptive Selection • Selection acts to remove the intermediate phenotypes favoring the extreme phenotypes:

17. Convergence • Convergence occurs when species evolve into a common phentoypic form due to a common need. For example the diagram below portrays a shark, ichthyosaurus, a penguin and a dolphin. These are fish, reptile. bird and mammal respectively (very different families of animals). Yet they all have a torpedo body shape, pectoral, caudal and dorsal fins. This is based on their common need to swim rapidly in an aquatic environment.

18. Divergence / Adaptive Radiation • Divergence occurs when species evolve in several directions away from a common ancestor. This happens usually to fill a vacant ecological niche. Also known as adaptive radiation.

19. Convergence and Divergence Together • By contrasting North American placental mammals with Australian marsupials. One can see how convergence and divergence works together. • In each case an ancestor mammal evolved into several ecological niches. • Since each niche required a specific phenotype, what results are 2 groups of mammals which have NEVER made contact, evolving into similar shapes.

20. Rates of Speciation: Two models exist to describe the rates of speciation. • Gradualism: • Refers to the model which holds that evolutionary change occurs in a gradual linear fashion. A species will change its morphology over time. • Punctuated equilibrium • Describes the process in which a species remains relatively unchanged for relatively long periods of time. Following which, a period of stress causes rapid change, followed by another period of relative stability.

21. Rates of Speciation:

22. Evidences of Evolution • Fossils: • Formed when animal remains are trapped in sedimentary layers. • Organic material replaced by minerals over millions of years. • Result is a "mineral cast" of the dead organism. • Where a fossil is located in the sedimentary strata can indicate it's age. • Successive changes in fossil forms of an organism can help in developing a fossil record of an organism's evolution. • Some rare fossils can show "soft tissues" which give invaluable information on an organism's physiology • Example: paleontologists recently discovered a dinosaur with a fossilized heart. This indicates that this species was most likely warm blooded. Fossilized Trilobite Fossilized Dinosaur Heart

23. Radiometric Dating: • Based on the fact that radioactive materials decay at a fixed rate. • Rate is known as a half-life: The amount of time in which only 1/2 of a radioactive sample remains • By measuring the amount of radioactive material in a fossil, one can determine how old it is. • Example is 14C dating. • 14C is an isotope of 12C which radioactively decays to 14N. • It occurs naturally in the environment, and is ingested by organisms while alive. • Once an organism dies, 14C intake stops, and the 14C begins to decay • One can then measure the amount of 14C remaining in a sample, and determine its age.

24. Similarities in Embryological Development • In early embryological development, it appears that embryos "play out" their evolutionary history. • Known as Ontonogy recapitulating Phylogeny. • Implies that genetically, we have not "forgotten" our evolutionary history, only built upon it.

25. Homologous Structures • Refers to the fact that organisms' structures are formed from similar anatomy. • Example the wing of a bird, arm of a man, wing of a bat, and flipper of a whale, all appear to be formed from a common set of bones. • Implies that these organisms evolved from some common ancestor.

26. Vestigal Structures: • Refers to the fact that organisms have structures which are disused • These structures, however, a remnants of structures the organisms used earlier in their evolutionary history. • Examples: • Hip bones in whales • Tail in humans • Appendix in humans • Legs/hips in snakes