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Chapter 22: Descent with Modification - A Darwinian View of Life Essential Knowledge 1.a.1 – Natural selection is a major mechanism of evolution (22.2). 1.a.4 – Biological evolution is supported by scientific evidence from many disciplines, including mathematics (22.3). Evolution The processes that have transformed life on earth from its beginnings Change in genetic make-up over time Gradual appearance of biological diversity Illustrates science as a PROCESS Evolutionary Adaptation An accumulation of inherited characteristics that enhance an organisms ability to survive and reproduce Involves populations – group of animals of same species that live in same geographic area Pre-Darwinian Views 1. Greeks 2. Fixed 3. Catastrophism 4. Hutton and Lyell 5. Lamarck Greek Philosophers 1. Plato - Organisms are already perfectly adapted to their environment 2. Aristotle - Organisms arranged on a “scale of life” from simple to complex Fixed, unchanging Ladder of Life Result: Greek No evolution Life is already perfect and doesn’t need to change All the rungs on life's "ladder" are already occupied. Fixed Species The creator had designed each and every species for a particular purpose. Coincides with Old Testament Says Earth is only5-6,000 yrs old (according to the Bible) Result: Fixed Species No Evolution! Created the viewpoint that all species could be identified and named (Taxonomy). A major factor in the Linnaeus classification system Similarities showed pattern of creationism (not an evolutionary pattern) Catastrophism Georges Cuvier (1769-1832). Attempted to relate fossils to current life Paleontology started Noticed: Deeper fossils were less similar Catastrophism Idea Fossils were the remains of species lost due to catastrophe No new species originated; species could only be lost over time Each rock/strata boundary represented a catastrophe Catastrophe destroyed all/many species Created a mass extinction Result – No evolution! James Hutton Geologist Related living organisms and their changes to changes in the Earth 1795 - Gradualism Profound change is the cumulative product of slow, but continuous process Result: Gradualism Changes on the Earth were gradual, not catastrophic. Gradual mechanisms change living organisms (and Earth) Charles Lyell Geologist 1797 - 1875. Incorporated Hutton’s gradualism into a theory called Uniformitarianism. Uniformitarianism idea Geological processes have operated at the same rate over the Earth’s history These processes are STILL occurring today More comprehensive theory (involved past AND present) Result: Uniformitarianism The Earth must be VERY old. (much older than 6000 years of the fixed species concept). Idea that slow and subtle processes can cause substantial change over time Jean Baptiste Lamarck Published theory in 1809. Theory - Life changed from simple to complex over time Lamarck Fossils were the remains of past life forms Used fossils to create of descent Evolution did occur. His two mechanisms were incorrect Mechanisms 1. Use and Disuse Body parts used to survive become larger and stronger Body parts not used to survive deteriorate. Ex: giraffe (neck was constantly stretched to reach leaves) Mechanisms 2. Inheritance of Acquired Characteristics Modifications acquired by use/disuse were passed on to offspring Ex: muscular arms (you work out and therefore your children will be muscular) Problem w/ Lamarck He had no prior knowledge of genetics (hadn’t been “discovered” yet) Acquired traits are not transmitted offspring Lamarck claimed animals have an innate drive to become more complex (not better adapted!) Lamarck’s Credits Did suggest correctly the role of fossils in evolution Did suggest that adaptation to the environment is a primary product of evolution Problem: timing (too fast!) Charles Darwin Father of the modern theory of evolution Theory Descent with Modification. Darwin's Background Trained as a Naturalist (after trying religion and medicine). Was a poor student Quit medical school (to become clergy man and ship naturalist) Voyage of the Beagle Result: Voyage Became interested in geographic distribution of species (why certain animals live where they do?) Visited: Brazilian jungles, Galapagos islands, Argentina, Antarctica, Andes Mtns Allowed him to formulate and support his ideas on Natural Selection Galapagos Finches Beaks and behaviors have adapted to specific foods available on specific islands Island Tortoises Neck lengths have adapted to foods on specific islands Marine Iguanas Adapted swimming/walking adaptations to be successful both in water and on land Alfred Wallace 1858 Wrote paper on natural slection Ideas were identical to Darwin's. Waited to publish (wrote to Darwin w/ ideas) Result - July 1, 1858 Dual presentation of the Wallace-Darwin ideas to the Linnaean Society of London. Lyell presented 1859 – Darwin published (solo) the “Origin of Species” Comment Darwin best remembered for the theory because of his overwhelming evidence and because he published 1st! Wallace could have received credit for his ideas (but he idolized Darwin and wanted him to get the attention) Darwinian View History of life is like a tree with branches over time from a common source Current diversity of life is caused by the forks from common ancestors Example Most branches are dead ends! 99% of all species are extinct “The Origin of Species” Documented the occurrence of evolution Suggested that the mechanism for evolution was Natural Selection. Conclusion: Biological diversity was/is the product of evolution “The Origin of Species” Focused on diversity of organisms Includes: geographic distribution, adaptations, origins Two points: 1) Ancestral descendants 2) Natural selection is mechanism for evolution The Theory of Evolution Based upon 5 major facts/observations Helps to devise 3 evolutionary inferences Evolution: The Facts: Fact 1 - All species reproduce themselves Until resources limit this growth The Facts, cont: Fact 2 – Most populations are normally stable in size Fact 3 – Natural Resources are limited (finite). Inference 1 Use Facts 1, 2, 3 The large number of offspring must compete for the limited resources Result - Most offspring will die! More Facts Fact 4 – No two individuals in a population are exactly alike Fact 5 – Variation is inherited Inference 2 Use Facts 4, 5 Those individuals whose inherited characteristics fit them best to their environment will survive and reproduce! Inference 3 Use Facts 4, 5 Offspring inherit the favorable characteristics Populations shift over time as the favorable characteristics accumulate Thomas Malthus Demographer (geographic distribution and population growth) Helped Darwin to develop these inferences Nature Nature: Food, shelter, disasters, climate Determines which characteristics are favorable Favors some, while filtering others Determines who will survive! Result - “Natural Selection” Artificial Selection When man determines the characteristics that survive and reproduce Result - the various breeds of animals and plants we’ve developed. Genetic engineering! Evolution Success Measured By: Survival rate Reproductive rate (success) Whoever lives long enough and has kids is the “winner” in evolution. Requirements for Natural Selection In order for Natural Selection to work, you must have: Long periods of time Variations within a population Subgroups of Natural Selection 1. Populations are the units of Evolution (NOT individuals) 2. Only inherited characteristics can evolve (traits passed from parent to offspring) 3. Natural selection is always operating (based upon environmental factors) Comment Some acquired characteristics may allow a species to evolve "outside" of natural selection Ex: culture, learning, diet, exposure to mutagens Nature vs. nurture Visible Signs of Evolution 1. Biogeography 2. Fossils 3. Taxonomy 4. Comparative Anatomy 5. Comparative Embryology 6. Molecular Biology Biogeography The geographical distribution of species Problem: Species mixtures on islands Marsupials in Australia Biogeography Closely/Evolutionarily-related species tend to be found in the same geographic region However, the same niches (in differing regions of the world) are usually occupied by species that may have evolved similar adaptations – but are DIFFERENT species Ex: sugar glider and flying squirrel **Both have adapted similar adaptations (skin flaps) but are NOT closely related to each other. They have evolved this adaptation independently ** Islands often contain ENDEMIC species (species that are found NO WHERE ELSE in the world!) **Why? Islands are a perfect example of how geography influences evolution Evolution Viewpoint Biogeographical patterns reflect descent from the ancestors that colonized the area Fossils Relics or impressions of organisms from the past Problem: Show changes over time from simple to complex Many fossils don't have descendants Evolution Viewpoint Life has changed over time Many species failed to survive and became extinct Comments: Fossils 1. Fossilization is a rare event 2. Only hard parts fossilize well 3. Problem in finding fossils 4. Interpretation. 5. “Missing links” Taxonomy Science of Classification. Using various characteristics – group organisms by like characteristics Main Categories Domain Kingdom Phylum or Division Class Order Family Genus Species Comparative Anatomy 1. Homologous Structures Common "building plan” with divergent functions Mammal forelimbs Comparative Anatomy Whale Legs 2. Vestigial Organs Rudimentary structures of marginal, if any, use. Human Example Evolution Viewpoint Remodeling of ancestral structures as their functions or adaptations changed Comparative Embryology Problem - closely related organisms go through similar stages in their embryonic development Ex: Gill pouches in vertebrates All animals go through these stages of development!! Evolution Viewpoint Ontogeny is a replay of Phylogeny. (Development reflects descent) Molecular Biology Study of Evolution at the DNA or protein levels Problem - related species have similar DNA sequences Evolution Viewpoint Related species share a common ancestral DNA. The closer the relationship, the more similar the DNA sequences should be. Summary Recognize viewpoints of evolution preceding Darwin, and identify their main points and characteristics. Identify the assumptions, inferences and outcomes of Darwin's Theory of Natural Selection. Recognize the signs of the process of evolution through the mechanism of natural selection.