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Chapter 4

Textbook Chapter 4 - The Evolution and Classification of Species

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Esteban Parra

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Notes From Reading C HAPTER  4: HE  EVOLUTION  AND  CLASSIFICATION OF  PECIES  PGS . 85­106) Introduction - When so-called creation scientists dispute evolution, they generally mean macroevolution - Creationism argues that we cannot directly observe changes over millions of years and therefore cannot conduct scientific tests - We rely on some record – geologic strata or stellar configurations - Geology makes use of the fact that geologic processes occur in a regular manner and so occurred in the same way in ancient times o Available information about current geologic processes helps explain patterns of change in the past - Evolutionary science takes what we know about microevolution and extends it to explain the long-term pattern of macroevolution The Birth and Death of Species - The origin of new species has been observed in historical times and in the present - Charles Darwin sought to explain the basic nature of evolutionary change, believing that extension of these principles could explain the formation of new species What Is a Species? - Biological Species Concept –Adefinition of species that focuses on reproductive capabilities, whereby organisms from different populations are considered to be in the same species if they naturally interbreed and produce fertile offspring o Note: organisms from different populations must be capable of interbreeding. These matings must occur in nature and take place naturally (ie. tiger and lions mate in zoos but don’t breed together in nature). The offspring must be fertile, capable of producing further offspring. - Example: Mules are farm animals produced as the offspring of a horse bred with a donkey o They interbreed naturally (satisfying the first and second part of the definition) o Mules are sterile and cannot produce further offspring o Since not fertile, the horse and he donkey are considered separate species - The biological species concept assumes that two organisms either belong or do not belong to the same species (no intermediate state) - Problem: if some populations of speciesAevolved into species B, at what point did those populations stop being speciesAand start being species B? o Species concept suggests that this change was instantaneous, because a creature belongs to either one species or the other o In real world, the evolution and variation work to break down rigid systems of classifications Species Change - Asingle species can change over time such that enough differences accumulate that we would choose to give it a different species name o Anagenesis – the transformation of a single species over time - Chronospecies – Labels given to different points in the evolutionary lineage of a single species over time. As a species changes over time, the different stages are labeled as chronospecies in recognition of the biological changes that have taken place o In evolution, chronospecies are different stages in the evolution of a single evolutionary lneage - Cladogenesis – The formation of one or more new species from another over time Notes From Reading C HAPTER  4: THE EVOLUTION  AND  CLASSIFICATION OF  SPECIES  PGS . 85­106) - The problem of species naming is complicated by the fact that evolutionary relationships among fossil forms are not always clear Speciation - For a species to become a new species, these genetic differences must be great enough to prevent successful interbreeding with the original parent species - For this to occur, the population must become reproductively isolated from the original parent species Reproductive Isolation - Reproductive Isolation – The genetic isolation of populations that may render them incapable of producing fertile offspring o The genetic change that can lead to an inability to produce fertile offspring - The first step in speciation is the elimination or reduction of gene flow between populations (populations must be genetically isolated from one another for speciation to occur) o Speciation – The origin of a new species - Common form of isolation in animal species: geographic isolation o Two populations are separated by a physical barrier, (I.e., river or mountain range, great distances) - Populations may be isolated by behavioral differences such as feeding habits o Some groups may eat during the day, and other during dusk o Since groups aren’t in frequent contact with one another, there is opportunity for isolation to develop Genetic Divergence - Other evolutionary forces must act upon this isolation to produce a situation in which the isolation groups have changed sufficiently to make fertile interbreeding no longer possible - Isolation does not always lead to speciation - Mutation might act to increase variation among populations as it occurs independently in the genetic composition of separate groups - Genetic drift also contributes to differences in allele frequencies among small populations - Fossil record shows that there are times when evolutionary change is slow, and times when it is fast (in geologic terms) Adaptive Radiation - Adaptive Radiation – The formation of many new species following the availability of new environments or the development of a new adaptation - Example: Darwin finches – the availability of new environmental niches led to the rapid speciation of finches in the Galapagos Islands Extinctions and Mass Extinctions - It is estimated that more than 99 percent of all species that ever existed have become extinct - The exact causes of a species’death vary from situation to situation - When the environment changes too rapidly or when the appropriate genetic variations do not exist, a species can become extinct - Mass Extinction – Many species becoming extinct at about the same time o Fossil records documents 5 mass extinctions in the history of our planet (some are suggesting we are currently in a period of extinction that might be the sixth) Notes From Reading C HAPTER  4: THE  EVOLUTION  AND  CLASSIFICATION OF  SPECIES  PGS . 85­106) - Mass extinctions can be caused by a relatively
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