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BIOL202 - Lectures 16-20

BIOL202 - Lectures 16-20 - Differences in body proportions...

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Differences in body proportions showing adaptation to prevailing climates in Homo sapiens . On the left is an male from a group of arctic Inuit people (formerly referred to as “Eskimos”). On the right is a male native from the Sudanese Nile area in Africa. The tall, thin body of the Sudanese native results in a higher surface area-to-volume ratio which allows for increased dissipation of heat. Note that in addition to having a smaller overall body size, another way to increase the body’s surface to volume ratio is to have a long, thin morphology form with long, thin appendages. The shorter, squatter body of the Inuit results in a lower surface area to volume ratio which helps conserve heat. How did the evolution of different body plans occur?
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LECTURE 16: NATURAL SELECTION I HOW EVOLUTIONARY CHANGE OCCURS Darwin argued: - Species are not immutable; normal "form" of organisms in a species or population can and will change over time. - Modification of the normal form of individuals occurs in response to changes in biotic and abiotic environmental conditions - The species or population evolves new morphological, physiological and behavioral traits that facilitate survival and reproduction in the changed environment - These beneficial traits are called "adaptations" - Different populations of the same species occupying different environments will come to differ in form as they adapt – become "fit', over time, to local environmental conditions - Individuals in different populations of a species can become so different in form that they essentially become unique species; this is the "adaptive radiation" of a species into many species - Adaptive radiation of species has occurred over and over in the history of life giving us the millions of species we have today But how does modification of the "normal form" of organisms in a population occur? How do populations adapt to changes in their environment? Darwin: Adaptation occurs through process called natural selection.
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Logic of Darwin's theory of " evolution by natural selection " Observation : Every species has enormous reproductive potential . In most species, if all offspring produced each year survived to breed themselves, the species would quickly cover the Earth with their kind. Observation : But numbers of no species increases endlessly; resources are in limited supply ; there are limits to the number of individuals the environment can support. Obvious conclusion : Species can and often do produce far more offspring than the environment can support. This leads to intraspecific competition and a “struggle for existence”. Only a fraction of offspring produced in each generation will survive and reproduce . Observation : Individuals in populations are not identical in form; individuals vary in morphology, physiology, behavior.
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