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Transcript
CHAPTER 22 DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE Evolution : processes that have transformed life on Earth from its earliest forms to the vast diversity that characterizes it today. *diversity of organisms *origins and relationships *similarities and differences *geographical distribution *adaptations to surrounding environment HMS Beagle Who was Charles Darwin? 1809 - 1882 Captain Fitzroy’s traveling companion on the Beagle Hated Was a Medicine ‘substitute’ and Hated almostConfrontations did not get on the HMS Spent Beagle time collecting beetles, catching rats, ….. Geologist, zoologist, paleontologist, naturalist Hated being in the ministry Author of the book “Origin Was called a “disgrace to of Species” thethe family” by his father Robert Darwin! Said - writing it was “Like Confessing a Murder”! VOYAGE OF THE HMS BEAGLE : 1831 - 1836 Fossil record Created by impressions of organisms that existed in the past Fossils in sedimentary rock – show succession of organisms through time (includes transitional forms and extinctions) Slow and subtle processes persisting for long periods of time can add up to substantial change - Geology records this before ‘evolutionary’ theories (plate tectonics, mountain building/erosion……) Jean Baptiste Lamarck: the outcaste! used the fossil record as evidence proposed a theory of evolution where organisms became better and better Mechanism - ”use” and “disuse” leads to: inheritance of acquired characteristics (you ‘acquire’ a phenotype in your lifetime and pass it on to your kids) also means environmental influences can be inherited DON’T BE LAMARCKIAN! FOR YOU WILL BE DISSSSED……. BUT WAIT, NOW, Epigenetics makes Lamarck a new Hero!!!! (oh you did not hear that as far as your not-so -current AP exam goes - stomp with glee on Lamarck all you want!) Carolus Linnaeus: --founded taxonomy and the genus/species system of naming organisms Homo - genus sapien - species AHEM! NOTICE THEY ARE BOTH MALE! DOMAIN Kingdom Country Phylum State Class County Order Town Family Neighborhood Genus Street Species House Number King Philip Came Over For Getting Stoned (yikes!) Observation: 13 or so species of finches on different Galapagos islands; these finches resembled the South American (mainland) finches more than say finches in Asia…. Can you summarize how EVOLUTION occurred to produce separate populations of large and medium beaked Ground Finches in Galapagos Islands? Medium Ground Finch (smaller beak) Large Ground Finch (Larger Beak) Microevolution: changes in allele frequencies (=how often you see a particular phenotype) from generation to generation Speciation/Macroevolution: Evolution of distinct species (that cannot mate) One population of birds on one island After a long time, there are now 2 islands and 2 populations with a reproductive barrier (geographic). many insects in tree holes lots of plants (with hard to crack seeds) The birds adapt to their niche and cannot mate anymore = 2 different species! many insects=long beak lots of plants with seeds=large beak What did Darwin Say? Descent with modification (diverse life forms have risen from a common ancestor) (the CONCLUSION) Descent occurs through the process of Natural selection (the HOW?) Observations: All populations would increase exponentially if all individuals reproduce successfully. Populations tend to remain stable in size. Environmental resources are limited. Inferences: There is competition for resources – the “struggle for existence” Only a small fraction of the population survives Observations: Individuals in a population have varying characteristics. Much of this variation is heritable. Inferences: Survival depends on inheriting the “best fit” physical traits (“reproductive fitness”) This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics Island with many many insects accumulating over the generations. Darwin’s main ideas : 6 steps KNOW THIS INSIDE OUT! 1) All populations will try to increase in time; Resources are limited (intraspecific competition results). Struggle for existence follows. 2) There is an unequal ability of individuals to survive and reproduce - this is ‘variation’ based on genes/epigenome. 3) Natural Selection acts on this inherent VARIATION allowing the “best fit” to survive and pass on their genes. 4) The product of natural selection is the adaptation of populations of organisms to their environment. (= edits the variation to exclude ‘unfit’ individuals) 5) This adaptation is inheritable - so the next generation continues to express that ‘best fit’ trait and then in time….. 6) New species formed as sufficient adaptations accumulated in time such that they could no longer mate with the ancestral species 1) Descent with modification - all present day organisms have descended from ancestors by the accumulation of adaptations through natural selection Descent with modification - the conclusion. Descendents accumulated diverse modifications or adaptations that fit them to specific ways of life and habitats - resulting in formation of new species. All present day organisms are related through descent from unknown ancestors in the past. DESCENT WITH MODIFICATION – CORE OF DARWINIAN THEORY -More descent: Organisms are related through descent from common ancestors So….. All organisms in a CLASS have a common ancestor at the level of the PHYLUM and so on… • This evolutionary tree of the elephant family is based on evidence from fossils. Fig. 22.7 Fig. 22.9 Apply the concept of Natural Selection and predict what will happen to these beetle species in this new environment Fig. 22.9 Apply the concept of Natural Selection and predict what will happen to these beetle species in this new environment • For example, these related species of insects called mantids have diverse shapes and colors that evolved in different environments. Fig. 22.10 Artificial Selection: The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits. Short period of time needed for Artificial Selection What common EVOLUTION misconceptions do students have? Organisms “choose” to evolve better traits (Lamarckian) Natural Selection causes variation Natural selection acts on ALL variation Natural Selection acts on individuals and therefore individuals evolve What is EVOLUTION? Evolution is measured as the change in relative proportions of heritable variation in a population over a succession of generations. Is there evidence for evolution? Insecticide resistance AIDS Pepperred moth Homologies (Anatomical Embryological Molecular) Biogeography Fossil Record 2a) Natural selection in action: the evolution of insecticideresistance occurs in nature - individuals with the best fit genes that can resist the insecticide will survive…. Fig. 22.12 2b) Natural selection in action: the evolution of drugresistant HIV - 3TC drug resistance developed - 100% HIV become resistant in 3-4 weeks! 2c) Natural selection in action: the peppered moth - originally light colored on light bark; Industrialized England - bark became covered in soot; so bark became dark; moth evolved to become dark 3a) Anatomical -human hand, cat limb, whale flipper, bat wing - they all have the same basic bone structure and design; they have ALL evolved from B)SoHOMOLOGIES – a common ancestor with a similar ‘limb design’. Related to this: Similarities in characteristics resulting from common ancestry is known as are homology. 3b) Genetic Homologies: Homeoboxes a common set of developmental genes seen in species as diverse as the fly to 1) Homologous Structures: Same skeletal mammals! elements, but different functions Same ancestor- tetrapod forelimb. HOMOLOGOUS STRUCTURES 3b) Molecular Homologies Basic genetic Code (all organisms) and…. Ontogeny recapitulates phylogeny what ever does this mean? Ontogeny recapitulates phylogeny what ever does this mean? Ontogeny recapitulates phylogeny - the phylum origin is ‘recapped’ in the embryo 3c) Embryological Homologies - embryos look alike in related species! All vertebrate embryos have ‘pharyngeal pouches’ in their throat. These in the Adult become gills of fish or the Eustacean tubes in other vertebrates! Homologies mirror the tree of life. 3d) Vestigial organs, structures that are not used, but which had important functions in ancestors - still retained in descendents, so evolution ‘happened’. Some Alleged Vestigial Organs in Man Tonsils Coccyx (tail bone) Thymus Little toe Nipples on males Nodes on ears "Darwin's points" Pineal gland Adenoids Nictitating membrane of eye Appendix Wisdom teeth Parathyroid Ear muscles for wiggling Body hair 3d) Vestigial organs – spurs in snakes, hind leg bones in whales. 4) Fossil Evidence- Capture evolutionary transitions - all species not present at the same time 5) Biogeography- The geographical distribution of species . Species tend to be more closely related to other species from the same area than to other species with the same way of life, but living in different areas CONVERGENT EVOLUTION 5) Biogeography- extension- Island species related to mainland species As Darwin said, “There is grandeur in this view of life.” Fig. 22.18