What is? The Modern Theory of Evolution 5/3/2012. Evolution Series: Set 3. What is evolution?

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1 Evolution Series: Set 3 Copyright 2005 Version: 2.0 What is? What is evolution? Permanent genetic change (change in gene frequencies) in populations of individuals. IDoes not refer to changes occurring to individuals within their own lifetimes.. : smallscale changes within gene pools over generations. : large scale changes in form, as viewed in the fossil record, involving whole groups of species and genera. The Modern Theory of Evolution Combines the following ideas: Darwin s theory of the origin of species by_. Understanding of -Mendel basis of heredity-weismann + + Darwin Mendel Weismann 1

2 The Concepts of : descendants of ancestral forms adapt to different environments over long periods of time. Mechanism for adaptation is Bases for Natural Selection: Natural Selection Populations produce too many young: many must die Individuals show variation: some variationsare more favorable than others Natural selection favors the best suited at the time Variations are inherited. The best suited variants leave more offspring. Evidence for Evolution Evidence comes from many sources: : identification, interpretation & dating of fossils--some of the most direct evidence of evolution. : study of embryonic development in different organisms & its genetic control. _: study of the morphology of different species. Paleontology Comparative anatomy 2

3 The Record A, but incomplete, record of evolutionary history: species can be traced through fossil relatives to origins. species often similar to, but differ from, species. types often differ between rock layers. Numerous species found as fossils. Fossils can be to establish their approximate absolute. fossil types mark changes in past conditions on Earth. Rates of evolution can vary, with bursts of species formation followed by stable periods. These fossil teeth, from Mastodon, an extinct elephant, are similar to the deciduous teeth of modern elephants. The Archaeopteryx Fossil Eight well-preserved fossil specimens have been discovered in fine-grained limestone in Germany (dated late Jurassic, about 150 million years ago). Reptilian Features Forelimb has three functional fingers with grasping claws. Avian Features Vertebrae are almost flat-faced. Lacks the reductions and fusions present in other birds. Impressions of feathers attached to the forelimb. Breastbone is small and lacks a keel. Belly ribs. True teeth set in sockets in the jaws. Incomplete fusion of the lower leg bones. The hind-limb girdle is typical of dinosaurs, although modified. Long, bony tail. Impressions of feathers attached to the tail. LEFT: Archaeopteryx lithographica Found in 1877 near Blumenberg, Germany Fossils in a Profile rock layers arranged in order in which deposited the most layers nearer the. layers can be disturbed by tectonic activity. Rock layers containing fossils allows us to arrange fossils in (order of occurrence), Does not give date. Most recent sediments Oldest sediments Recent fossils are found in recent sediments Numerous extinct species Fossil types differ in each sedimentary rock layer New fossil types mark changes in environment Only primitive fossils are found in older sediments 3

4 Fossils Relative age of fossils is useful, but fossils provide reliable historical data only if we can determine their absolute age. A number of methods are used to date fossils. Dating Method Age Range (years) Material Dated Electron Spin Resonance Bone, tooth enamel, cave deposits Fission Track 1 million Volcanic rock Obsidian Hydration present Obsidian (volcanic glass) Amino acid racemization 1 million 2000 Bone Thermoluminescence less than Pottery, fired clay, bricks, burned rock Uranium/Thorium Less than Bone, tooth dentine Carbon Bone, shell, charcoal Potassium/Argon million Volcanic rocks A fossil trilobite, a primitive arthropod that dwelled in the seas of the Devonian period 370 million years ago Anatomy 5 digit limbs found in most vertebrates have the same general. Similarity of structure is called. Homologies indicated ancestry. Forelimb Humerus (upper arm) Ulna Radius Carpals (wrist) Metacarpals (palm) Hind Limb Femur (thigh) Fibula Tibia Tarsals (ankle) Metatarsals (sole) Phalanges (fingers) Phalanges (toes) Note that forelimbs and hind limbs have different names for equivalent bones. Structures Basic 5-digit limb has been highly modified to serve specialized functions. Such homologies also indicate Basic limb plan has been adapted to meet the needs of different niches. Bird's wing Bat's wing Mole's forelimb Dog's front leg Seal's flipper Human arm 4

5 Structures Not all inherited from a ancestor. Structures having same function in different organisms may come from different origins. This phenomenon is termed analogy. structures do not imply evolutionary relationships, may indicate. Examples: Eye structure in octopus and mammals. Wings in birds and butterflies. Fins in fish and flippers in mammals Flippers Wings Fins Organs _structures that no longer perform the same function as in other organisms. These organs must have been important in some ancestral form, but became. Selection pressure for complete loss is weak so the structures remain apparently have little use, may perform some secondary function. Kiwis: wings Snakes: pelvic girdle and hind limbs. Eyes of burrowing animals no longer used for vision. Appendix in humans Wisdom teeth Face & Ear Muscles Vestigial Organs in Descendants of large, fourlegged land mammals took up an aquatic existence some 60 million years ago. Over many millions of years, the pelvis and femur of whales have become very small and no longer fulfill a locomotory function. Femur Pelvis Hindlimb Forelimb 5

6 Evidence Lemurs are endemic to the island of Madagascar distribution Basic principle-- each plant and animal species originated only once. The place where this occurred is the centre of origin. The range of a species can be very restricted or, as with humans, almost the whole world (cosmopolitan). Regions that have been separated from the rest of the world for a long time (e.g. Madagascar, Australia, and New Zealand), often have distinctive biota comprising a large number of endemic species (species that are found nowhere else). Map: University of Texas at Austin (Public Domain image) Distribution of species around the world suggests that and spread out (radiated) out into new environments. Good examples are found on _: Galapagos Islands Cape Verde Islands Tristan da Cunha Species thought to be closely related on other evidence found to have greater of DNA in common. Humans and chimpanzees have a in their DNA sequences and are very closely related. DNA of humans and chimpanzees more closely matched than. 6

7 Sequences of amino acids in certain proteins (e.g. and ) have revealed great similarities and specific differences between species. related species have proteins with. Amino acid sequences are determined by & differences are due to. degree of similarity determined number of mutations related species have had more time for Phe Glu Ala Met Tyr Iso Phe Ala Gly Ser Ala Glu Amino acids Hemoglobin Amino acid differences for beta-hemoglobin in primates compared to the human sequence: Squirrel monkey Gibbon Rhesus monkey Primate No. of amino acids different from humans Position of changed amino acids Chimpanzee Identical Gorilla Gibbon Gorilla Rhesus monkey Squirrel monkey Chimpanzee The 'position of changed amino acids' is the point in the protein, composed of 146 amino acids, at which a different amino acid occurs. Evidence Relationships of a large number of different animal groups have been established on basis of immunology. 7

8 UV Light Various forces or phenomenon are at play in the evolutionary process: At the level: Control of gene expression Rate of At the level: mutations Polyploidy Aneuploidy Egg Sperm At the level: Environmental modification of phenotype Reproductive success Selection pressures 'Fitness' of the phenotype 8

9 At the level: Genetic drift and population size altering gene frequencies selection aa aa aa competition effect (gene flow) aa At the level: barriers isolation (prezygotic and postzygotic) pressures competition 9