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a201-11f-06-HowSpeciesArise - Introduction to Biological...

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Introduction to Biological Anthropology: Notes 6 What are species and how do they arise? Copyright Bruce Owen 2011 - Two ways to look at evolution - We can look at it up close - What we see in the close-up, short-term, detailed view is called microevolution - Microevolution = evolution within a species (changes in a population that do not result in a new species) - like the evolution of beak depth in a species of finches - after two years of drought, they were still finches, but were finches with slightly deeper beaks - or we can step back and look at long-term changes that are visible in the fossil record - What we notice in the long-term view is the appearance of new species - that is, the kind of evolution that produces the many different, distinct kinds of plants and animals we see today - Macroevolution = evolution that creates new species - Darwin suggested that the accumulation of a lot of small microevolutionary changes ought to add up to bigger, more obvious differences - Eventually, to entirely new species - given enough time, the accumulation of microevolutionary changes in many different populations ought to create countless different species with all sorts of different features - Macroevolution is what Darwin originally set out to explain: - what led to the profusion of different species of plants and animals, each adapted to its environment? - Hence the title of his seminal book: “On the Origin of Species” - But first, what are “species”? - Preliminary definition: Species are (usually) easily distinguishable types of organisms (I’ll define this better later) - The notion of species has two key parts - individuals of the same species are similar to each other - individuals of one species are different from individuals of other species - there are (usually) no intermediate types - no gradation from one species to the other, but rather a gap - no intermediate forms that are hard to classify as one or the other species - there are gorillas and there are chimps, but no “gimps” or “chorillas” - this is curious - why are there distinct kinds of organisms (species), rather than a continuous gradation of characteristics from one kind to the next? - why are there no chorillas? - by and large, species are real categories that exist in nature - unlike many categories used by scientists, species aren’t just invented for the sake of convenience
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Intro to Biological Anthro F 2011 / Owen: What are species and how do they arise? p. 2 - living things really fall into distinct, well-defined categories - Even so, there are a number of different definitions of species. - amazingly enough, there is actually still a lot of debate about what these distinct kinds of organisms really are - and although they seem easy to observe, in some cases there is still room for disagreement - for a summary of some of this debate, see: - http://www.talkorigins.org/faqs/speciation.html - we will consider just the two most interesting of the leading concepts of species: - the biological species concept - the ecological species concept - But first, we need to understand two useful ideas -
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a201-11f-06-HowSpeciesArise - Introduction to Biological...

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