Darwinian Evolution Chapter 22

What you need to know! How Lamarck’s and other notable predecessors’ views of the mechanism of evolution differed from Darwin’s. The difference between structures that are homologous and those that are analogous, and how this relates to evolution. The role of adaptations, variation, time, reproductive success, and heritability in evolution.

Preceding Darwin Aristotle 384-322 BC – Scala naturae: oragnization of life based on increasing complexity Linnaeus 1707-1778 – taxonomy: naming and classifying all organisms, binomial nomenclature: genus and species Cuvier 1769-1832 – father of paleontology, study of fossils leads to theory of catastrophism (mass extinction) which explains the boundaries between strata and the location of different species

Preceding Darwin Hutton 1726-1797 & Lyell 1797-1875 – Theory of Gradualism (uniformitarianism): Earth geology changes slowly and continuously The Earth must be VERY old Darwin studied Lyell’s work

Preceding Darwin Lamark 1744-1829 – 1st theory of evolution Use or disuse of body parts leads to their development or deterioration (acquired characteristics) Inheritance of acquired characteristics

Early Darwin 5 year voyage on the HMS Beagle 1831-1836 Naturalist – collected plants, animals, and fossils Major finds on the Galapagos Islands Finches Tortoises Common ancestor

Late Darwin “Origin of Species” Natural variation exists in all populations All organisms produce many offspring with variations All organisms compete for limited resources Natural Selection Descent with modification

Artificial Selection Human selection of favorable traits over 100’s of generations Darwin used this model to develop natural selection and descent with modification

Natural Selection Darwin’s mechanism for evolution is natural selection (an explanation for adaptations) What was Lamark’s mechanism? Adaptations: characteristics that enhance an organisms ability to survive (i.e. desert fox – large ears; arctic fox – small ears) Organisms that have advantageous heritable traits (fitness) survive and reproduce at a higher rate Environmental changes may result in adaptations, and sometimes speciation (the founder effect) Individuals do not evolve, Populations do!

Descent with Modification Offspring are genetically different from their parents As we move forward in time diversity increases (speciation) As we move backward in time diversity decreases (fewer species) If we go back far enough all species are related (ancient common ancestor)

Evolution Summed Up Evolution is change in species over time. Heritable variations exist within a population. These variations can result in differential reproductive success. Over generations, this can result in changes in the genetic composition of the population. Individuals do not evolve! Populations do!

Patterns of Evolution Divergent Evolution Convergent Evolution 2 different species evolve from a common ancestor (different adaptations) Convergent Evolution Different species show the same adaptations due to similar environments (analogous structures) Parallel Evolution 2 different animal groups evolve similarly in separated environments (mammals and marsupials) Coevolution Both predators and prey adapt to each other over time