EVOLUTION I. Evolution accounts for the diversity of life on Earth Evolution = change over time process by which modern organisms have descended from ancient organisms II. Theories of Evolution A. Scientific theory a well supported testable explanation of natural phenomena a. ex: gravity, plate techtonics b. NOT a guess or hunch B. Jean-Baptiste Lamarck theory of evolution 1809 a. Lamarck s theory: by selective use or disuse of organs, organisms acquired or lost traits during their lifetime; these traits could then be passed on to their offspring b. ex: giraffe and long neck c. problem: Lamarck did not know how traits were inherited C. Charles Darwin contributed more to our understanding of evolution than anyone a. over time, natural selection results in changes in inherited traits of a population III. Ideas that shaped Darwin s thought on evolution A. Made observations, collected evidence in Galapagos Islands off coast of S. America; voyaged on boat called HMS Beagle in 1831 o observed similar species well suited to the environment they inhabited o traits of similar species varied noticeably among different island of the Galapagos ex: tortoises and finches o hypothesized that animals adapted to local conditions on islands after their arrival B. James Hutton and Charles Lyell studied geology in early 1800 s helped scientists recognize that Earth is many millions of years old; older than anyone believed A. Thomas Malthus and human population growth 1798 a. if the human population continued to grow unchecked sooner or later there would be insufficient living space and food creating struggle to survive B. Farmers and artificial selection a. nature provides the variation humans select those variations they find useful i. ex: cows and milk production, hogs and muscle, horses and speed
IV. Evolution by natural selection proposed by Darwin in On the Origin of Species, 1859 A. Struggle for existence more offspring are produces than can survive; members of each species compete to obtain food, living space, and other necessities of life B. Survival of the fittest = Natural Selection a. individuals with an adaptation that makes them more fit for a certain environment will survive and reproduce b. adaptation -- inherited characteristic (trait) that increases an organism s chance of survival i. ex: bird or mammal (rabbit, fox, squirrel) turns white in winter in the north c. fitness ability of an individual to survive and reproduce in its specific environment C. Descent with modification each living species has descended, with changes, from common ancestor V. Evidence of evolution A. fossil record examples of many species that have lived for a time and then became extinct B. geographic distribution of living species looking at similar environments on different continents, different animals have similar anatomy and behavior because of adaptation a. ex: beaver (N. America) and capybara (S. America) i. muskrat (N. America) and coypu (S. America) C. homologous (similar or corresponding) body structures structures that have different mature forms but develop from the same embryonic tissues a. strong evidence that all 4-limbed vertebrates have descended from a common ancestor D. vestigial organs organs so reduced in size that they are just vestiges (traces) of homologous organs in other species a. ex: tail bones, appendix (?), tiny leg bones in boas and pythons, wisdom teeth, hip bones in whales E. similarities in embryology early stages (embryos) of many vertebrate animals are very similar F. components of genetic code and amino acids sequences show evolutionary relationships. a. DNA bases (ATCG) b. Converting glucose to ATP for energy
VI. EVOLUTION OF POPULATIONS (Chapter 16 p. 392-410) A. Population a group of individuals of the same species that interbreed Gene pool all the genes of all the members of a particular population (all alleles) Evolution (in genetic terms) = any change in the relative frequency of alleles in a population B. Sources of genetic variation 1. Mutations change in the sequence of DNA; if beneficial mutation trait will increase in population 2. Recombination genes combining in new ways during the production of gametes for sexual reproduction and crossing over (Meiosis). 3. Gene Flow transfer of genes between populations Ex: people moving to another country or the migration of animals to another population. VII. EVOLUTION AS GENETIC CHANGE A. Evolution by Natural selection: -acts on entire populations not just individual organisms. -never acts directly on genes entire organisms survive to reproduce, or die and do not reproduce. Single-gene and Polygenic Traits 1. Single-gene: natural selection on single gene traits can lead to changes in allele frequencies and thus to evolution. Ex: polydactyl (6 fingers) versus normal digit number (5 fingers) 2. Polygenic Traits: effects on allele frequencies much more complex a) Directional selection individuals at one end of curve have higher fitness Ex. anteater s long tongue; big beaks can feed on large seeds b) Stabilizing selection individuals near center of curve have higher fitness Ex. Human baby weight at birth too small low survival, but too large difficult birth c) Disruptive selection upper and lower ends of curve have higher fitness Ex. large and small seeds common birds beaks are large or small B. Gradualism and Punctuated Equilibrium 1. Gradualism: change that occurs in a species at a slow steady pace 2. Punctuated equilibrium: rapid sudden change in a species Ex: light brown and black pocket mice after volcanic eruption in New Mexico
C. Genetic Drift a random change in allele frequency Certain individuals may leave more descendants than others, and over time this can cause an allele to become common in the population. Caused by chance, not natural selection. VIII. Speciation formation of a new species -Species group of organisms that breed with each other and produce fertile offspring in the natural environment A. How do new species arise? 1. Reproductive isolation= when members of two populations cannot interbreed and produce fertile offspring. 2. How does reproductive isolation occur: barriers to gene flow are created. I. behavioral isolation courtship rituals or other behaviors are different ex: Eastern meadow lark will not respond to Western meadowlark mating songs II. geographic isolation population separated by geographic barrier like river ex: one population of squirrels divided into 2 or more smaller populations by formation of Grand Canyon III. temporal isolation populations reproduce at different times can be different seasons or time of day ex: plant species that flower at different times of the year; toad species that live in same area, but one species mates in early summer and other in late summer 3. Darwin s finches an example of speciation - descended from a common ancestor from mainland S. America - natural selection shaped beaks as they adapted to different foods in different islands B. Divergent Evolution process of 2 or more related species becoming more and more dissimilar ex: red fox and kit fox --red fox lives in forest where red color blends with trees; kit fox lives in deserts where its light brown color blends in with sandy environment --similarity in structure indicate a common ancestor, but as they adapted to different environment the appearance of 2 species diverged C. Convergent Evolution unrelated species become more and more similar as they adapt to same kind of environment ex: Cactus growing in American desert resembles cactus which grows in African desert. Both have fleshy stems for storing water and spines to ward off predators.
EVERYDAY EVOLUTION: Antibiotic Resistant Bacteria Evolution is a process which requires genetic varieties, large population changes, and long periods of time. Thus, it is very challenging to see evolution occur in one lifetime. Can you think of a modern day example of evolution you ve encountered? Certain species of bacteria are common examples of potentially life threatening evolution. Recall that bacteria are tiny, unicellular, prokaryotic organisms. Bacterial reproduction occurs through a quick and simple form of asexual mitosis. This form of reproduction can occur at alarming speeds and has given bacteria the ability to evolve in short periods of time! View the diagram below. Harmful (disease causing) bacteria can be treated using antibiotic drugs, which destroy bacteria if taken correctly. However, some bacteria have resistance to antibiotics due to random genetic mutations. This small population of bacteria, if left untreated, could reproduce and create a new antibiotic resistant strain. Using the above information and previous knowledge, let s analyze the following questions and scenarios: 1. Are bacteria living or non-living? Do they contain genetic material? Living, DNA 2. What causes new species of bacteria to arise in a population? Genetic mutations in DNA 3. Doctors inform patients to take all of their antibiotics even if symptoms subside. What are doctors attempting to reduce or avoid? A patient could still have antibiotic resistant survivors. If these bacteria are able to reproduce inside of the body, a new generation of antibiotic resistant bacteria will form. If these bacteria spread to numerous individuals, there will be no treatment for this infection. A superbug could form and cause significant damage. 4. In recent years, agricultural industries have started injecting their livestock with antibiotics to increase muscle tissue growth. What concerns could be raised to the agricultural industry about the overuse of antibiotics? The agricultural industry could cause our arsenal of antibiotics against current bacteria to become ineffective.
Phylogeny Darwin s ideas about descent with modification have given rise to the study ofphylogeny, or evolutionary relationships among organisms. Understanding a phylogeny is a lot like reading a family tree. The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of that ancestor. As you move from the root to the tips, you are moving forward in time. When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages. Speciation to form a new biological species from an existing one Misconceptions about Humans: The phylogeny of living species most closely related to us looks like this: It is important to remember that: Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human.