Darwin's Theory - Natural Selection - Biology PDF

7.2: Darwin’s Theory Return from The Voyage  Darwin (with collaboration from Alfred Wallace) presented his mechanism for evolution based on his findings  One year later in 1859, he published his famous book The Origin of Species The Origin of Species  Two major points:  1) All sp...

7.2: Darwin’s Theory Return from The Voyage  Darwin (with collaboration from Alfred Wallace) presented his mechanism for evolution based on his findings  One year later in 1859, he published his famous book The Origin of Species The Origin of Species  Two major points:  1) All species of organisms living on Earth today are descended from ancestral species  In other words, species __evolve over time____  2) The mechanism that causes species to change over time is ____natural selection____ 1) All Organisms Are Descended From Others  Proposed the major concept of __descent with modification____  Definition: descendants of the earliest organisms spread into various habitats over millions of years and accumulated different modifications, or adaptations  The term ____evolution____ now replaces ‘descent with modification’  Descent with modification explains the diversity of life  Ex. Insects with a common ancestor have different adaptations that allow them to survive in their unique environments (i.e. different camouflage patterns) Camouflage 2) Natural Selection  Theory of natural selection based on 3 major observations:  a) the struggle for existence  b) variation  c) the role of the environment a) The Struggle for Existence  Relatedto Malthus’ idea that species produce more offspring than there are resources in nature  Hence, there is a ‘struggle for existence’ amongst individuals of a population  In most cases, only a small percentage of offspring survive every generation and go on to reproduce  Ex. Pandas produce two to three offspring at a time but usually only one survives due to limited milk production by the mother b) Variation  Variation: differences among members of the ____same species__________  Sometimes a certain variation is best suited to a specific envrionment______________  Individuals with this heritable variation are more likely to produce the most offspring  This variation will become __more common_ over many generations b) Variation c) Role of the Environment  Theenvironment selects individuals in a species with variations that are best suited ______for that environment____ Theory of Natural Selection Natural selection: process by which individuals with inherited characteristics well suited to their environment leave more offspring than individuals with adaptations less suited to the environment Theory of Natural Selection Theory of Natural Selection Survival of the Fittest  Fitness: an individual’s ability to survive and reproduce in a specific environment  Survival of the Fittest: individuals in a population with increased fitness will survive and reproduce the most successfully  Synonym for _____natural selection_________  Note: Natural selection does not make organisms ‘better’; an adaptation might work well in one environment but not so well in another Case Study: The Peppered Moth  Theremust be genetic variation in order for natural selection to occur. There are two forms of the peppered moth prevalent in England. typica carbonaria Case Study: The Peppered Moth  Thelighter colored moth is more difficult to spot against typical tree bark, while the darker moth stands out and makes easier prey. typica carbonaria Case Study: The Peppered Moth Peppered  At Moths the beginning of the industrial revolution in England, coal burning produced soot that covered the countryside of some areas. Peppered Moths Case Study: The Peppered Moth  Now the white moths stand out, while the black moths are hard to see. The black moths are more likely to survive and pass on the genes for dark color to offspring. Over time, the black moths became more common than the white moths. Summary  Evolution according to Lamarck:  Giraffes grew longer necks during their lifetime; this adaptation could be passed on to offspring  Evolution according to Darwin:  Some giraffes would have been born with long necks and some with short (there is _____variation_________)  The environment would have selected for giraffes with long necks (they have higher ____fitness______) Natural Over Many Selection Generations Variation Individuals Evolution of a among with population members of favourable, a species heritable adaptions Troubleshooting  Populations evolve, individuals do not!  Species survive because they adapt, they don’t adapt in order to survive  An adaptation is a characteristic that is heritable; an adaptation that may be useful in one environment may not be in another  Natural selection is the mechanism for evolution  Evolution is not the same as speciation; a population can evolve without creating a totally different species Homework  Answer the following questions:  1) Explain what Darwin meant by ‘descent with modification.’  2) How did Darwin use Malthus’ work to formulate his theory of natural selection?  3) What makes an organism more ‘fit’ than others?  4) How does natural selection depend on variation?  5) Why do distantly related species in different places share similar traits?  6) Lamarck hypothesized that evolution moves species toward perfection. Why is this statement incorrect?