Darwins Theory of Evolution by Natural Selection Section
Darwin’s Theory of Evolution by Natural Selection Section 15 -1 and 15 -2
What is evolution? • Evolution – Change over time – The process by which modern organisms have descended from ancient organisms.
What is a theory? • Theory – A well-supported testable explanation of phenomena that have occurred in the natural world.
The theory of evolution by natural selection • The evidence is overwhelming that evolution (change over time) has occurred. • A vigorous debate remains, however, over the relative importance of different mechanisms that drive evolution.
The education of Charles Darwin by the natural world
The education of Charles Darwin by the natural world • Huge variety of living things. • Organisms are well-suited to their environments. • Distributions of some types of living things are puzzling.
The education of Charles Darwin by the natural world • Fossils – the preserved remains of ancient organisms. • Fossils showed how distributions of organisms changed over time.
The education of Charles Darwin by the natural world • The Galapagos Islands became the single most important stop on Darwin’s journey.
Galapagos Islands – 1000 km west of Peru.
Galapagos Islands • Distant from any other land. • Variety of environments on different islands. • Different communities of plants and animals on different islands. • Variations of similar animals that were specific to one island or another.
Questions that shook the foundation what Darwin thought he knew • Had the similar animals been members of the same species at one time? • Had these original species come from the mainland? • If the species had changed, how or why had this occurred?
üCheckpoint • Evolution is what? üChange over time • What is a scientific theory? üA well-supported testable explanation of natural phenomena.
üCheckpoint • What were some of the important observations made by Darwin on his voyage around the world? üVariety üOrganisms well-suited to environments üPuzzling patterns of distribution üfossils
üCheckpoint • Characteristics of the Galapagos Islands? ü Distant from any other land. ü Variety of climates on different islands. ü Different communities of plants and animals on different islands. ü Variations of similar animals that were specific to one island or another.
15 -2 • Ideas that shaped Darwin’s thinking
Ideas that were “in the air” among European scientists and intellectuals • The Earth was much older than had previously been thought. – James Hutton • Geological forces shaped the Earth • These must have taken millions of years
Ideas that were “in the air” among European scientists and intellectuals • Charles Lyell – Scientists must explain past events in terms of processes that they can actually observe presently. • Volcanoes • Erosion • Glaciers • Etc.
Ideas that were “in the air” • Thomas Malthus – English economist – Noticed that babies were being born faster than people were dying. – If human populations continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
Malthus
Ideas that were “in the air” Malthus • Darwin realized that plants and animals would be even more influenced by this Malthusian phenomenon than were humans because of their larger number of offspring. Charles Darwin
Ideas that were “in the air” • Jean-Baptiste Lamarck – Proposed that by selective use or disuse of organs, living things acquired or lost certain traits during their lifetime. – These traits could then be passed on to their offspring. – Over time, this led to change in a species.
Ideas that were “in the air” • Jean-Baptiste Lamarck – Why isn’t Lamarck treated by history in the same way or better than Darwin? – He had the misfortune of being wrong about the mechanism of evolution (inheritance of acquired characters).
Ideas that were “in the air” • Was Darwin uniquely insightful or was theory of evolution by natural selection inevitable given what others were writing and thinking at the time?
Alfred Russel Wallace
üCheckpoint • Hutton üGeological forces shaped the Earth and therefore the Earth must be very old. • Lyell üScientists must explain past events in terms of processes that they can actually observe.
üCheckpoint • Lamarck üThe inheritance of traits modified by use or disuse. • Malthus üLeft unchecked, populations will quickly outgrow their resources.
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