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Chapter 3

Chapter 3 Macroevolution and Evolutionary Anthropology.docx

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Michael Schillaci

Chapter 3 – Macroevolution and Evolutionary Anthropology Macroevolution – large scale changes at or above the species level, extending over geological era, and resulting in the formation of new taxonomic groups. Species and Speciation Speciation – evolutionary process involving the formation of a new species Individuals can vary greatly yet still be considered one species (dogs) Typological species concept – similar-looking individuals lumped into discrete categories Modified typological species concept – similar-looking individuals that can successfully produce fertile offspring lumped into discrete species categories Individuals are the same species if they can successfully produce fertile offsprings (no longer favoured) because …  Fails to account for geographic variations  Erroneous conclusion that males of the same species, or conspecific males, represent different species (two males cannot reproduce)  Distinct species can reproduce to form hybrids There are two definitions of species, which has a strong relevance to evolutionary anthropology 1. Biological species concept (BSC) th  First introduced in the 20 century  Introduced by geneticists and researchers who study the diversity of life  Traits may be shared between different species  One species cannot breed with another species  Ernst Mayr (1942) – biological species are actual/potential interbreeding populations which are reproductively isolated from other such groups  Must apply all known morphological, behavioural, and ecological data to use as deductive proof of reproductive isolation between species  BSC does not account for fossil species 2. Phylogenetic species concept (PSC)  There are three versions of the PSC  Species aggregation of sexual populations diagnosable by unique combination of character states  Requires researchers to measure and analyze character states of a sample of individuals and between populations  Can be applied to living organisms and fossils 1 Cladistics – system of biological taxonomy based on the quantitative analysis of comparative data that is used to reconstruct the phylogenic relationships and evolutionary history of groups of organisms Cladistics is a response to weaknesses with phonetics (classification of organisms based on shape and appearance – fails to distinguish species level differences) Speciation Controversies  Is speciation an adaptive or a non-adaptive trait  How does natural selection and genetic drift effect speciation Speciation can occur by natural selection, mutations, and genetic drift Genetic drift increases the variation between populations and decreases the variation between populations Allopatric speciation – species formation that occurs following the geographic isolation of populations Physical barrier causes geographic isolation and reduced gene flow Anthropologist and biologist believe that this is the most common process that can result in speciation There are two modes of allopatric speciation: vicariant and peripatric Vicariant speciation – occurs when a physical barrier creates large, geographically separated populations  the populations diverge and can no longer interbreed Peripatric speciation – occurs when small, peripherally isolated colony of main population diverges to become new species The differences between the two is the population size And the extent of separation between the populations Introduction to Cladistics All life on earth are connected to one another creating a tree of life Cladistics – study of evolutionary relationships among organisms on our planet Cladogram (phylogeny/evolutionary tree)– A branching diagram used to illustrate phylogenetic relationships (evolutionary relationships among organisms) Cladistics includes three main assumptions about the relationship among organisms  Changes in characteristics, which are the genetic and physical features of an organisms, within lineages over time  All organisms are descended from a common ancestor  When lineage split, it divides into exactly two groups 2 Data used to create cladistics trees In some cases researchers use total evidence (employs a set of morphological and molecular data)  issues with fossils Most phylogenetic analyses of fossils a based on teeth Until statistical procedures were developed morphological data differed from molecular data. Biological evolution can produce homoplastic characters – A feature in two or more taxa whose similarity is not due to common descent Phylogenetic analyses should be hypotheses not facts Reading and Interpreting Cladistic trees The two commonly used cladograms are: diagonal cladogram (evolutionary relationships based on angled lines) and rectangular cladogram (evolutionary relationships, employs rectangular bifurcations (junctions)). In both cladograms there are six taxa present (A-F) these letters represent species
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