Theory of Evolution 15.2 Evidence of Evolution
How??? Fossils give us evidence for evolution. Problem: HOW DO LIVING ORGANISMS PROVIDE EVIDENCE FOR EVOLUTION? Solution: morphology (similarities in shape and structure), embryology (development), DNA, RNA and protein sequences.
Geologic Time Scale Evidence #1
Fossils • Remains of organisms that died long ago • Can form under different conditions and in differing time periods • Very powerful evidence even today • Steno = superposition • Superposition says that undisturbed areas of the earth form in layers from bottom to top, oldest to newest • These layers contain fossils • The Geologic Time scale was developed to summarize these findings
Fossils, cont. • Relative age of fossils can be determined by comparing fossils found in these layers • Absolute age of fossils can be determined by radiometric dating • An incomplete history – there are gaps which leave questions about evolution and how it occurred
Fossils, cont. • Strata tell us that different organisms lived at different times • Organisms from the past in some cases were very much NOT like organisms today • Fossils in adjacent layers are more like one another than those farther away • Fossils provide clues as to an organism’s environment
Fossils, cont: Transitional Species • These are species that help us fill in gaps in the time scale • They allow us to make inferences between what we think existed at particular time periods and what later descendants • Whales evolved from land mammals???
Biogeography Evidence #2 • Studies where organisms live around the world • Darwin and Wallace both noticed two things: ***closely related animals living in different environments – Australian mice, cats, wolves with pouches ***unrelated animals living in similar environments– Australian mice, cats, wolves with pouches Descent with modification at work
Anatomy and Embryology • Structure and development • Ancestor vs. relative – descending from ape OR descending from a common ancestor • Descent from your cousin, or from your grandparent • Common structure, common ancestor, different environment, different adaptations • Homologous structures: related structures with different functions due to different adaptations - different patterns of evolution forced selective environmental pressures amongst related organisms • Analogous structures: related structures have similar functions but no common ancestor – bird, bat, moth wing – different patterns of evolution forced selective environmental pressures • Vestigial structures: left over structures which currently serve no purpose in us but do in related organisms Evidence #3
Anatomy and Embryology, cont. Homologous structures
“Ontogeny Recapitulates Phylogeny” • Ernst Haeckel – zoologist 1834-1919 • An organism's biological development, or ONTOGENY parallels and summarizes its species' entire evolutionary development, or PHYLOGENY
Biological Molecules • Organisms that share traits have a more recent ancestor • Still developing
15.3 Evolution in Action • Evolution can produce new species of organisms, especially if there are new habitats to invade • When many related species evolve from a single ancestral species, this is called adaptive radiation • Divergent evolution is the process of two or more related species becoming more and more dissimilar. Adaptive radiation is a type of divergent evolution (homologous structures). • Example: Galapagos finches, Hawaiian honeycreepers, anole lizards
Evolution in Action, cont. • On the other hand, it is possible for unrelated species to become more and more similar in appearance as they adapt to the same kind of environment. This is called convergent evolution (analogous structures). • Examples include this cactus and spurge (euphorbia): Notice the resemblance of the cactus (upper left), which grows in the American desert, to the euphorbia, which grows in the African deserts. Both have fleshy stems armed with spines. These adaptations help the plants store water and ward off predators.
Artificial Selection • Where humans choose what their offspring will look like by selecting the parents for certain traits • All domesticated dogs today arose a common wolf ancestor from Eastern Asia about 15,000 years ago
Coevolution • When two or more species evolve together because they influence each other • Examples: bees and flowering plants, predator – prey, humans and antibiotics
Closure Identify each type of evidence (puzzle pieces) for evolution in the following examples: • Mammalian embryos have gill slits • Human blood proteins are very similar to chimps • Domestic chickens are descended from jungle fowl of SE Asia • All clams have two shells, right and left