The Theory of Evolution

1. The Theory of Evolution SBI3U0

2. What is a Scientific Theory? • The word ‘theory’ has two different meanings • The colloquial one and the scientific one • Colloquial meaning • In regular speech, a theory often means “an educated guess” used to explain an observation • This is more akin to a hypothesis in science • Scientific meaning • A scientific theory is a model that accounts for and explains a large set of experimental evidence • A theory provides a basis for us to understand and predict natural phenomenon

3. What is a Scientific Theory? • The most important part of a scientific theory is that it makes testable predictions • This allows us to put the theory to the test, through experimentation, to try and prove it wrong • If a theory has not been falsified in this manner through several years of experimentation and observation it is generally accepted to be true • Does this mean scientific theories are facts? • NO! • A theory is an explanation of evidence. If new evidence arises that does not follow what the theory predicts, the theory is either incomplete or incorrect and must be fixed or replaced with a new theory that accounts for all of the evidence

4. What is a Scientific Theory? • This process of revision is ongoing and has occurred with all of the theories your are familiar with • Eg: The atomic theory • Dalton: Atoms are hard spheres, elements are different types of atoms • Explains bonding patterns in molecules • Thompson: Atoms contain positive and negative charges • Explains the fact that charged particles can be emitted from atoms • Rutherford: the protons are contained in a nucleus • Gold foil experiment • Bohr: The electrons orbit the nucleus in energy shells with specific energies • Explains atomic emission/absorption spectra • Quantum Theory: Wave-particle duality, Heisenberg uncertainty principle, etc...

5. What is a Scientific Theory? • Eg: The cell theory • Hooke: Viewed plant cell walls through a microscope • Leeuwenhoek: Viewed live cells through a compound microscope • Schleiden and Schwann: Cells are the basic units of life, all organisms are made of one or more cells • Virchow: Cells come from pre-existing cells • Explained the inability of life to spontaneously appear

6. What is a Scientific Theory? • Each of these theories have been revised over and over • This was to account for new observations as technology improved, and as new experiments were designed • Now, the two theories accurately explain such a wealth of observations that they are accepted by all scientists • Both theories have also made accurate predictions countless numbers of times throughout history • This does not mean they are 100% correct, but it would be astounding if either was fundamentally wrong • Given all of the evidence that supports them

7. The Theory of Evolution • The Theory of Evolution • Is as solid a theory as that of the atom or the cell • It has been tested countless times and is supported by a wealth of evidence • What is evolution and what does the theory say? • The theory of evolution explains the mechanisms that cause species to change over time (or evolve) • That species change over time is a FACT, as we will see with some of the following evidence • The theory explains HOW this evolution occurs

8. Selective Breeding • Selective breeding is the most common example of species evolving over time • Dogs have been domesticated from wolves • Fruits and vegetables have been bred for their desirable traits, producing tastier fruit, more robust plants, etc... Wild Tomato Selectively Bred Tomato

9. Selective Breeding Red Cabbage Broccoli Brussels Sprouts Cabbage Cauliflower Kale Wild Sea Cabbage

10. Bacterial Resistance • Bacterial populations can change their resistance to antibiotics after exposure • The bacteria go from not being resistant, to have some resistance, to being highly resistant over the course of several generations • There are several other examples, some of which we will see as we discuss the mechanisms of evolution, but first we must discuss some of the history behind the theory

11. History of Evolution • Previous Thought • As far back as ~350BC (Aristotle) to the 1700s, living things were widely thought to be immutable (unable to change) • From the 15th-18th century, philosophers recognized the importance of careful observation, experimentation, and deductive reasoning (Copernicus, Galileo, Newton, etc...) • Carl Linnaeus (1707-1778) and Erasmus Darwin (1731-1802) (Charles Darwin’s grandfather) suggested that life changed over time • But they no explanation of why/how

12. Lamarck • Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (1744-1829) developed two principles that, while flawed, led to the discovery of the true mechanisms of evolution • He postulated the principles of use and disuse and the inheritance of acquired characteristics • Use and disuse: structures that are used frequently become larger, while those that are not shrink • Inherited characteristics: individuals can pass on their acquired skills/characteristics to their offspring • Eg: a giraffe who elongated its neck slightly to reach higher branches could produce children with slightly longer necks • This has been shown to be untrue, and we will see why

13. Fossil Evidence • Around the same time as scientists were researching life, geologists were discovering fossil remains of long dead organisms • Fossils • Hard impressions of living organisms in solid rock • Fossils are formed when dead organisms sink to the bottom of a body of water • Sediment covers the body • The low oxygen content prevents decomposition • Over time, minerals slowly replace the organic material of the organisms body • This preserves a rock impression of the body

14. Fossil Evidence

15. Fossilization • Fossilization occurs very rarely • The conditions for fossilization are not common • There is often too much oxygen present, so organisms decompose too quickly to fossilize • Usually occurs only in aquatic environments • Organisms with soft tissues decompose very quickly • Harder tissues like shells and bones fossilize much more readily since they decay very slowly • Fossils can also occur when organisms become trapped in a material • Amber (fossilized sap), volcanic ash, and ice

16. Fossils • Fossils were originally thought to be recently living organisms that become trapped in muddy deposits and then hardened • This was quickly refuted by the following facts • Many fossils appear to be of unusual and unknown organisms (ie: dinosaurs, trilobites, etc...) • There are no fossils of most living species • Fossils are often buried deep within rock formations (some more than 1km deep) • Fossils are often found in unexpected locations (ie: marine organisms found high in the mountains and in deserts)

17. Paleontology • The discovery of fossils led to the invention of paleontology • The study of prehistoric life through fossils • There are two prominent scientists whose work provided evidence for evolution • Georges Cuvier, paleontologist • Charles Lyell, geologist

18. Fossils • Cuvier noticed a few important things when studying where fossils are found • Fossils of very simple organisms are found in all depths of rock • Fossils of more complex organisms are found only at shallower depths, in younger rock • Fossils in the shallower depths are more likely to resemble living species • Rock layers contain fossils of many species that do not occur in layers above or below them

19. Catastrophism • Cuvier’s observations offered strong support of the idea that organisms evolved from simple to complex over time • Since the oldest rocks contained the simplest fossils • Cuvier did not interpret his data quite this way • He developed the idea of catastrophism • This means that global catastrophes caused mass extinctions, and that new organisms were created afterwards • What doesn’t catastrophism account for? • Catastrophism doesn’t account for why the organisms changed from simple to complex over geologic time

20. Uniformitarianism • At about the same time, Charles Lyell (1797-1875) was interpreting the fossil record in a quite different manner • Lyell is commonly known as the father of modern geology due to his idea of uniformitarianism • The principles of uniformitarianism • Earth has been changed by the same processes in the past that are occurring in the present • Geological change is slow and gradual, rather than fast and catastrophic • Natural laws that influence these changes are constant and eternal, and they operated in the past with the same intensity as they do today

21. Lyell • Lyell’s ideas were considered radical • Whole mountain ranges being formed gradually • Deep gorges being formed slowly due to erosion • This directly challenged the young Earth ideology of several religions • Lyell’s ideas are supported by a wealth of data, not the least of which being radioactive dating methods • The age of rock can be determined by the ratio of different isotopes • Radioactive isotopes decay (undergo nuclear reactions) at a constant and predictable rate

22. Enter Charles Darwin • By the nineteenth century (1800s), the stage was set for Darwin to study the evolution of living organisms • There was growing evidence for, and acceptance of, the ideas that; • The Earth was ancient • Life had an extremely long time over which to accumulate change • Charles Darwin spent a large portion of his life cataloguing different types of organisms from around the world

23. H.M.S. Beagle • In 1831 he set off on the H.M.S. Beagle to study life in South America • The H.M.S. Beagle was sent to map the coastal waters of South America • Darwin was sent along as a naturalist to study the rocks, minerals, plants, and animals of South America • He noticed several important things on his journey • Many of the fossils in SA resembled the organisms living there • On the Galapagos islands (formed by undersea volcanoes), no amphibians or mammals lived there • The species on different Galapagos islands only resembled each other (and SA species), but were not the same