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Evolution Ch 7 Pt 1 Wooly mammoth skeleton: Mammoths lived 2 million to about 9,000 years ago. They were about 9 to 15 feet tall. Where would scientists look for possible reasons for extinction? 5 mass extinctions 1 underway • Evidence of five major mass dying of life forms on Earth • Each is followed by a succession of distinctly different organisms which can survive in the absence of predecessors – Example: dinosaurs died » Gave way to rise of mammals » Eventually humans appear Fossil succession shows : Life, as we can best define it: • The definition must be “built” on descriptions that fit all living things. – Living things are both complex and organized – Living things grow and reproduce – Living things respond to stimuli – Living things acquire and use materials and energy – Living things have (use) DNA to store information Misconceptions about evolution: ?? Evolution proceeds strictly by chance ?? Evolved species must be more complex than the predecessor ?? Where are the missing links? ?? humans evolved from monkeys so monkeys should no longer exist Theory of Evolution • A theory explains a series of observations and often unifies related facts through supportive evidence. • Evolution is based on the observed accumulated generation to generation changes within a defined group. • Evolution accounts for – similarities among life forms – differences among life forms Jean-Baptiste de Lamarck – (1744-1829) is best remembered for his theory of Inheritance of Acquired Characteristics: -- new traits arise in organisms because of their needs and repetitive behaviors to meet those needs – Acquired traits are somehow passed on to their descendants • Lamarck’s theory seemed logical at the time and was widely accepted Lamark’s Theory Rethinking… why would giraffes “develop” or actually “express” the trait of longer necks over time? Was the “acquired” trait passed on? Darwin • In 1859, Charles Robert Darwin (1809-1882) published On the Origin of Species – In it he detailed his ideas on evolution formulated 20 years earlier – he proposed a mechanism for evolution – From 1831 to 1836, he had traveled along the southern continents and Europe. What most don’t know about Charles Darwin • Darwin born in England on Feb. 12, 1809 – same day as Abraham Lincoln. • Father a doctor. Mother affluent (Wedgwood pottery family) . • Both families were free thinkers and philosophers. • His private school education was useless for his interests; his hobbies hunting, observing natural world, collecting things, and chemistry. About the same time….. – James Hutton was promoting his old earth and plutonic (igneous) rocks – and Abraham Werner promoted Neptunism (all rocks precipitate from oceans). – Darwin was exposed to Zoomania which promoted Lamarckian ideas. Learned taxidermy from a former black slave who inspired Darwin with his stories of the tropics. And a little more…. • Off to Cambridge, he studied to be a clergyman. Baptized into the Church of England, where it was compatible to be a naturalist. – He hunted, caroused, and collected beetles. – he learned to observe variations within a species from botanist and clergyman Professor Henslow. – Studied geology with Adam Sedgwick, a catastrophism proponent who later named the Cambrian system of rocks in England. – Learned to do field work and record observations meticulously. Darwin spent only 5 weeks in the Galapagos Islands. Here he made observations about distinct differences among similar animals that were directly related to food supply. He published his ideas in 1859, 24 yrs. later. Fig. 7-1, p. 115 Observation of finches in the Galapagos Islands Insect eaters Berry eater Insect eaters Seed eaters Cactus eaters What Darwin noticed • Plant and animal breeders practice artificial selection – breeding plants and animals with desirable traits • A process of selection among variant types in nature could also bring about change • Thomas Malthus’s timely essay on population suggested that human competition for resources and high infant mortality limited a population size Natural Selection (Key Points) The mechanism • Organisms in all populations posses heritable variations. – size, speed, agility, visual acuity, digestive enzymes, color, and so forth • Some variations are more favorable than others – some have a competitive edge in acquiring resources and/or avoiding predators • Not all young survive to reproductive maturity Those with favorable variations are more likely to survive and pass on their favorable variations Survival of the Fittest? • Natural selection is sometimes expressed as “survival of the fittest” “Survival of the Fittest” What does it mean?? • Misconception: • among animals only the biggest, strongest, and fastest are likely to survive – Maybe these traits are an advantage-- but natural selection may favor species other than the obviously bigger, stronger, or faster. Examples? Natural Selection involves differential rates of survival and reproduction Survival of the species depends on producing offspring. Again, rethinking……… the smallest if resources are limited the most easily concealed those that adapt most readily to a new food source those having the ability to detoxify some substance Others? It helps to know what organisms had survived stressful conditions in the past …. The peppered moth Peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon During the Industrial Revolution in England, many of the lichens died out, and the trees that peppered moths rested on became blackened by soot, So, is “natural selection” the mechanism for evolution? • Natural selection works on existing variations in a population – It could not account for the origin of variations • Critics reasoned that should a variant trait arise, it would blend with other traits and would be lost • The answer to these criticisms existed even then in the work of Gregor Mendel, but remained obscure until 1900 Gregor Mendel • controlled genetic experiments with true-breeding strains of garden peas – strains that when self-fertilized always display the same trait, such as flower color • Traits are controlled by a pair of factors now called genes • Genes occur in alternate forms, called alleles – One allele may be dominant over another – Offspring receive one allele of each pair from each parent Mendels Work • The parental generation consisted of true-breeding strains RR = red flowers rr = white flowers • Cross-fertilization yielded a second generation all with the Rr combination of alleles, in which the R (red) is dominant over r (white) Mendel’s Work • The second generation, when self-fertilized produced a third generation with a ratio of three red-flowered plants to one white-flowered plant Why is this important? • The factors (genes) controlling traits do not usually blend during inheritance • Traits not expressed in each generation may not be lost even if not seen! • Some variation in populations results from alternate expressions of genes (alleles) – Variation can be maintained! – **Why is variation important to survival of a species? Modern Genetics Complex, double-stranded helical molecules of deoxyribonucleic acid (DNA) called chromosomes are found in cells of all organisms Specific segments of DNA are the basic units of heredity (genes) The number of chromosomes varies from one species to another fruit flies 8; humans 46; horses 64 Modern Thinking • During the 1930s and 1940s, – paleontologists, population biologists, geneticists, and others developed ideas that merged to form a modern synthesis or neo-Darwinian view of evolution • They incorporated chromosome theory of inheritance into evolutionary thinking – They saw changes in genes (mutations) as only one source of variation Most Importantly • They completely rejected Lamarck’s idea of inheritance of acquired characteristics • They reaffirmed the importance of natural selection • But since then, some scientists have challenged the emphasis in modern synthesis that evolution is gradual The Species • Species – a population of similar individuals that in nature interbreed and produce fertile offspring – Species are reproductively isolated from one another • Goats and sheep do not interbreed in nature, so they are separate species • When artifically bred in captivity, offspring are most often sterile. Remember… • Evolution by natural selection works on variation in populations – most of which is accounted for by the reshuffling of alleles from generation to generation during sexual reproduction • The potential for variation is enormous with thousands of genes each with several alleles (varieties), and with offspring receiving 1/2 of their genes from each parent • New variations arise by mutations – change in the chromosomes or genes Mutations • Mutations result in a change in hereditary information • ONLY mutations that take place in sex cells are inheritable, – Can be chromosomal mutations (affecting a large segment of a chromosome) – or point mutations (individual changes in particular genes) • Mutations are random with respect to “fitness” – they may be beneficial, neutral, or harmful to survival! The Species • Species – a population of similar individuals that in nature interbreed and produce fertile offspring – Species are reproductively isolated from one another • Goats and sheep do not interbreed in nature, so they are separate species • When artifically bred in captivity, offspring are most often sterile. Recipe for a species • Speciation is the process by which a new species arises from an ancestral species • It involves change in the genetic makeup of a population, – which also may bring about changes – in form and structure • During allopatric speciation, – species arise when a small part of a population becomes isolated from its parent population Insect eaters Berr y eater Seed Cactus eater eaters s Insect eaters Variations among “Darwin’s finches” were naturally selected from among the existing variations within the gene pool and mutations that may have occurred. What would cause the selection of the observed variations? Allopatric Speciation • Reduction of the area occupied by a species may leave a small isolated population – Two peripheral isolates evolved into new species (i.e. Darwin’s finches) How long does it take for changes to appear? • Although widespread agreement exists on allopatric speciation scientists disagree on how rapidly a new species might evolve • Phyletic gradualism- the gradual accumulation of minor changes which eventually bring about new species Punctuated Equilibrium holds that little or no change takes place in a species during most of its existence then evolution occurs rapidly Styles of Evolution • Divergent evolution occurs when an ancestral species giving rise to diverse descendants adapts to various aspects of the environment – Divergent evolution leads to descendants that differ markedly from their ancestors • Convergent evolution involves the development of similar characteristics in distantly related organisms • Parallel evolution involves the development of similar characteristics in closely related organisms Divergent Evolution Convergent Evolution Parallel Evolution Evolutionary Novelties • All land-dwelling vertebrate animals posses bone and paired limbs so these characteristics are primitive and of little use in establishing relationships among land vertebrates • However, hair and mammary glands are derived characteristics. – Only one subclade, the mammals, has them It wouldn’t be Geology without Death and Destruction….. 99% of all species that ever • Perhaps as many as existed are now extinct • Organisms do not always evolve toward some kind of higher order of perfection or greater complexity • Vertebrates are more complex but not necessarily superior in some survival sense than bacteria – after all, bacteria have persisted for at least 3.5 billion years • Natural selection yields organisms adapted to a specific set of circumstances at a particular time Extinction • The continual extinction of species is referred to as background extinction • It is clearly different from mass extinction during which accelerated extinction rates sharply reduce Earth’s biotic diversity • Extinction is a continual occurrence – …so is the evolution of new species that usually quickly exploits the opportunities another species’ extinction creates – Mammals began a remarkable diversification when they began occupying niches the extinction of dinosaurs and their relatives left vacant Extinction • The mass extinction of dinosaurs and other animals at the end of Mesozoic Era is well known…but not the greatest loss of biologic diversity! • The greatest mass extinction occurred at the end of the Paleozoic Era – end of Permian – More than 90% of all species died out – We will discuss these extinctions and their possible causes throughout the rest of the term Some predictions from the Theory of Evolution Oldest fossil-bearing rocks should have different organisms than more recent rocks There should be fossils connecting orders and classes of descendant organisms. Closely related species should be similar in anatomy, biochemistry, genetics Classification of organisms should show a nested pattern of similarities Isolated populations should closely resemble nearer populations rather than distant ones. Organisms should show a predicted succession in the fossil record: fish, reptiles, mammals Animals that diverged from a common ancestor should evolve to be more different over time Homologous or Analagous? • Homologous structures: – Similar structure – Different purpose • Analagous structures: – Distinctly different structures • Similar purpose Homologous or analagous? See Page 148 Text. Forelimb of humans, whales, bats Wings of birds, bats, flies