Patterns of Evolution Macroevolution largescale evolutionary patterns and

Patterns of Evolution

Macroevolution = large-scale evolutionary patterns and processes that occur over long periods of time. Six patterns: 1. extinction 2. adaptive radiation 3. convergent evolution 4. coevolution 5. punctuated equilibrium 6. changes in developmental genes

More than 99% of all species that have ever lived are now extinct. Effects of mass extinctions n provides ecological opportunities for organisms that survive n results in bursts of evolution that produce many new species

Extinction The extinction of dinosaurs, for example, cleared the way for the evolution of modern birds and mammals.

Extinction http: //www. pbs. org/wgbh/evolution/library/03/2/l_032_02. html Triassic layers are almost devoid of fossils, suggesting a mass extinction event occurred 250 million years ago, at the end of the Permian.

Adaptive radiation = the process by which a single species or a small group of species evolves into several different forms that live in different ways Examples: n Darwin’s finches – more than a dozen evolved from a single species. n On a larger scale, the disappearance of dinosaurs resulted in the adaptive radiation of mammals

Adaptive Radiation of Mammals

ADAPTIVE RADIATION DURING THE CAMBRIAN EXPLOSION (540 MYA)

Convergent Evolution = when unrelated organisms come to resemble each other Structures that look and function similarly but are made of parts that do not share a common evolutionary history are called analogous structures. For example, a dolphin’s fluke and a fish’s tail fin are analogous structures.

Occurs when organisms that are closely connected to one another by ecological interactions evolve together. Coevolution = when two species evolve in response to changes in each other over time. http: //www. pbs. org/wgbh/evolution/library/01/3/l_013_07. html Newt and snake

Coevolution Example: the orchid (unusually long nectar spur) and its moth pollinator (equally long feeding tube). How might natural selection bring about the evolution of this orchid and the moth?

Punctuated equilibrium = a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. -Small pop becomes isolated -Small group migrates -Mass extinctions open up new niches

Punctuated Equilibrium Darwin felt that biological change was slow and steady, an idea known as gradualism. - During the long history of life on Earth, evolution has often occurred at different rates for different organisms at different times.

“Hox genes, ” which all animals have, are the master control genes that guide development. Scientists can turn off and on hox genes during development to produce very large changes in adults. These small changes affect the timing of cell differentiation and gene expression and explain how so many different organisms evolved using the same set of genes.

Changes in Developmental Genes http: //www. pbs. org/wgbh/evolution/library/03/4/l_034_04. html