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Chapter 5

Textbook Chapter 5 Notes

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Heather Miller

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Notes From Reading CHAPTER 5:M ACROEVOLUTION :P ROCESSES OFVERTEBRATE AND M AMMALIAN EVOLUTION (PGS.95-114) Learning Objectives  Compare microevolution and macroevolution and explain how they are similar and how they differ  Describe how animals are classified and explain how humans fit into such classification as vertebrates and as mammals  Explain why evolutionary relationships are the basis for all scientific biological classifications  Explain what a fossil is and describe how different kinds of fossils are formed  Define the major characteristics of mammals, especially placental mammals  Explain how species are defined by biologists and how they originate from prior species Introduction  The bits and pieces of fossils are the remains of once living, breathing animals  We are primates, which in turn is one type of mammal and mammals are one of the major groups of vertebrates How We Connect: Discovering the Human Place in the Organic World  Classification – in biology, the ordering of organisms into categories, such as orders, families, and genera, to show evolutionary relationships  Multicellular organisms that move about and ingest food are called animals  Chordata – the phylum of the animal kingdom that includes vertebrates o Animals with nerve cord, fill slits and a supporting cord along the back  Vertebrates – animals with segmented, bony spinal columns; includes fishes, amphibians, reptiles (including birds) and mammals  Vertebrates are divided into five classes: cartilaginous fishes, bony fishes, amphibians, reptiles/birds, and mammals Principles of Classification  Taxonomy – is the field that specialized in establishing the rules of classification  For physical similarities to be useful, they must reflect evolutionary descendants  Evolutionary modification in structure occur with only relatively minor genetic changes o A few mutations in certain Hox genes in early vertebrates led to the basic limb plan seen in all subsequent vertebrates, including humans  Large anatomical modifications don’t always require major genetic rearrangements o Shows how we connect biologically with other life-forms, how our evolutionary history and thesis are part of the same grand story of life on earth  Homologies – similarities between organisms based on descent from a common ancestor  Both birds and butterflies have wings, but they shouldn’t be grouped together on the basis of this single characteristics  From quite distance ancestors, both butterflies and birds have developed wings independently  Analogies – similarities between organisms based strictly on common function, with no assumed common evolutionary descent  Homoplasy – the separate evolutionary development of similar characteristics in different groups of organisms o “Homo” = same and “plasy” = growth Constructing Classifications and Interpreting Evolutionary Relationships  Two major approaches when interpreting evolutionary relationships with the goal of producing classifications  (1) Evolutionary systematics – is the more traditional o A traditional approach to classification (and evolutionary interpretation) in which presumed ancestors and descendants are traced in time by analysis of homologous characters Notes From Reading CHAPTER 5:M ACROEVOLUTION :P ROCESSES OFVERTEBRATE AND M AMMALIAN EVOLUTION (PGS.95-114)  (2) Cladistics – emerged primarily in the last three decades o An approach to classification that attempts to make rigorous evolutionary interpretations based solely on analysis of certain types of homologous characters (those considered to be derive characters)  In recent years cladistics methodologies have predominated among anthropologists Comparing Evolutionary Systematics with Cladistics  Similarities between cladistics and evolutionary systematics o Both approaches are interested in tracing evolutionary relationships and constructing classifications that reflect these relationships o Both approaches recognize that organisms must be compared using specific features and that some of these characters are more informative than others o Both approaches focus exclusively on homologies  Differences between cladistics and evolutionary systematics o How characters are chosen o Which groups are compared o How the results are interpreted and incorporated into evolutionary schemas and classifications o Cladistics more explicitly and more rigorously defines the kinds of homologies that yield the most useful information  Some homologous characters are much more informative than other  Ancestral – referring to characters inherited by a group of organisms from a remote ancestor and thus not diagnostic of groups (lineages) that diverged after the character first appeared; also call primitive  In biological anthropology, the term primitive or ancestral simply means that a character seen in two organisms is inherited in both of them from a distant ancestor  Misinterpretation of ancestral characters can easily lead to inaccurate evolutionary conclusions  Cladistics focuses on traits that distinguish particular evolutionary lineages; such traits are far more informative than ancestral traits  Clade – a group of organisms sharing a common ancestor. The group includes the common ancestor and all descendants  Derived (Modified) – referring to characters that are modified from the ancestral condition and thus diagnostic of particular evolutionary lineages An Example of Cladistic Analysis: The Evolutionary History of Cars and Trucks  All “descendant” vehicles share a common ancestor  prototype passenger vehicle  The first major division differentiates passenger cars from trucks  Second split is between luxury cars and sports cars  Modified (derived) traits that distinguish trucks from cars might include type of frame, suspension, wheel size and in some forms, an open cargo bed  Derived characters that might distinguish sports cars from luxury cars could include engine size and type, wheel base size and a decorative racing stripe SUVs are basically trucks; the presence of a racing stripe could be seen as a homoplasy with sports cars  We need to be careful, looking at several traits, later deciding which are ancestral and which are derived and finally try to recognize the complexity introduced by homoplasy  Any modification in any species is constrained by that species’ evolutionary legacy – what species starts out with Using Cladistics to Interpret Real Organisms  Looking at the relationship of dinosaurs to birds  Traditionally it was thought that birds were a distinct group from reptiles and not especially closely related to any of them (including extinct forms)  The first fossil evidence of a very primitive bird was discovered in 1861 (two years after Darwin’s publication of Origin of Species)  The last two decades have supported the hypothesis that birds are closely related to some dinosaurs Notes From Reading CHAPTER 5:M ACROEVOLUTION :PROCESSES OF VERTEBRATE AND M AMMALIAN EVOLUTION (PGS.95-114)  Two developments in particular have influenced this change of opinion: o Discoveries in the 1990s from China, Madagascar and elsewhere o Application of cladistics methods to the interpretation of these and other fossils  Primitive birds from Madagascar show many other similarities to Velociraptor and its close cousins  There are traces of what were once feathers have been found embossed in fossilized sediments  Birds are not only descended from dinosaurs, they are dinosaurs (and reptiles) – just as humans are mammals, even though people are as different from other mammals as birds are from other reptiles  Strict cladistics analysis assumes that homoplasy is not a common occurrence; if it were, perhaps no evolutionary interpretation could be very straightforward  The proposed relationship between some dinosaurs and birds, the presence of feathers is an excelled example of a shared derived characteristics  therefore linking the forms  Shared Derived – relating to specific character traits shared in common between two life- forms and considered the most useful for making evolutionary interpretations  Cladistics analysis emphasizes that several characteristics should be examined, because homoplasy might muddle an interpretation based on just one or two shared traits  In the bird/dinosaur case, several other characteristics further suggest their evolutionary relationship  Phylogenetic Tree – a chart showing evolutionary relationships as determined by evolutionary systematics. It contains a time component and implies ancestor-descendant relationships  Cladogram – a chart showing evolutionary relationships as determined by cladistics analysis. It’s based solely on interpretation of shared derived characters. It contains no time component and does not imply ancestor descendant relationships.  Phylogenetic trees usually attempt to make hypotheses regarding ancestor-descendant relationships  Cladistics analysis makes no attempt whatsoever to discern ancestor-descendant relationships  Strict cladistics are skeptical that the evidence really permits such specific evolutionary hypotheses to be scientifically confirmed  Physical anthropologists use cladistics analysis to identify and assess the utility of traits and to make testable hypotheses regarding the relationship between groups of organisms  Aspects of both traditional evolutionary systematics and cladistics analysis are combined to produce a more complete picture of evolutionary history Definition of Species  Biological Species Concept – a depiction of species as groups of individuals capable of fertile interbreeding but reproductively isolated from other such groups  Speciation – the process by which a new species evolves from an earlier species. Speciation is the most basic process in macroevolution  According to the biological species concept, the way new species are first produced involves some form of isolation  Gene exchange between populations (gene flow) will be limited if a geographical barrier (Ie. Ocean) effectively separates these populations this is called Geographical Isolation  Genetic differences will accumulate in both populations  If population size is small, the genetic drift will cause allele frequencies to change in both populations  Since drift is random, we wouldn’t expect the effects to be the same  two populations will begin to diverge genetically  If gene exchange is limited, the populations can only become more genetically different over time  Behavioral differences that interfere with courtship – behavioral isolation Notes From Reading CHAPTER 5:M ACROEVOLUTION :P ROCESSES OFVERTEBRATE AND M AMMALIAN EVOLUTION (PGS.95-114) Interpreting Species and Other Groups in the Fossil Record  Each individual organism is a unique combination of genetic material, and the uniqueness is often reflected to some extent in the phenotype  Besides such individual variation, we see other kinds of systematic variation in all biological populations  Age changes alters overall body size, as well as shape, in many mammals  Sexual Dimorphism – differences in physical characteristics between males and females of the same species. o For example, humans are slightly sexually dimorphic for body size, with males being taller, on average, then females of the same population. Sexual dimorphism is very pronounced in many species, such as gorillas Recognizing Fossil Species  A species is a group of interbreeding or potentially interbreeding organisms that is reproductively isolated from other such groups  When studying fossil group, we may observe obvious variation, such as some individuals being larger and with bigger then than others  What is the biological significance of this variation? o Intraspecific – within species; refers to variation seen within the same population o Interspecific – between species; refers to variation beyond that seen within the same species to include additional aspects seen between two or more different species  If the amount of varia
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