BIOL1402 Chapter 14 Lecture

BIOL1402 Chapter 14 Lecture - 1 Chapter 14 The Origin of...

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1 Chapter 14 Chapter 14 The Origin of Species 2 Introduction ± An ancestral cormorant species is thought to have flown from the Americas to the Galápagos Islands more than 3 million years ago. ± Terrestrial mammals could not make the trip over the wide distance, and no predatory mammals naturally occur on these islands today. ± Without predators, the environment of these cormorants favored birds with smaller wings, perhaps channeling resources to the production of offspring. 3 DEFINING SPECIES 4 14.1 The origin of species is the source of biological diversity ± Microevolution is the change in the gene pool of a population from one generation to the next. ± Speciation is the process by which one species splits into two or more species. – Every time speciation occurs, the diversity of life increases. – The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago. 5 14.2 There are several ways to define a species ± The word species is from the Latin for “kind” or “appearance.” ± Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions. – How similar are members of the same species? – What keeps one species distinct from others? 6 14.2 There are several ways to define a species ± The biological species concept defines a species as – a group of populations, – whose members have the potential to interbreed in nature, and – produce fertile offspring. – Therefore, members of a species are similar because they reproduce with each other. 7 14.2 There are several ways to define a species ± Reproductive isolation – prevents members of different species from mating with each other,
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– prevents gene flow between species, and – maintains separate species. – Therefore, species are distinct from each other because they do not share the same gene pool. 8 14.2 There are several ways to define a species ± The biological species concept can be problematic. – Some pairs of clearly distinct species occasionally interbreed and produce hybrids . – For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears. – Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild. – Reproductive isolation cannot usually be determined for extinct organisms known only from fossils. – Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually. – Therefore, alternate species concepts can be useful.
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BIOL1402 Chapter 14 Lecture - 1 Chapter 14 The Origin of...

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