Chapter 22 Descent with Modification Evolution change in a population of organism over a long period of time o Change in genetic composition of a population Change in any aspect of an organism under genetic control biochemistry morphology behavior Scala naturae scale of nature that life forms were organized by increasing complexity St Augustine of Hippo 354 430 o Rationalized Christianity o Philosopher who proposed that god created the universe in a form unlike today but with the potential to develop into present day conditions Would take a long time programed universe o Problems with his model Supernatural cannot be tested Catastrophism events in the past happened suddenly and were caused by mechanisms different from those operating in the present Lamarck s idea of evolution First testable theory of evolution o inheritance of acquired characteristics o Use and disuse parts of the body used more often will become larger and stronger Snakes stopped using legs so they became weaker and eventually disappeared o Organisms can pass these traits to their offspring o Organisms have an innate desire to become more complex o Testing of the model Use and disuse does work to an extent muscles will get larger with more use Only changes in the germ cells can be passed down Darwin 1809 1882 o Beagle went to map the coast of south America and ended up at the Galapagos Saw 13 species of finch vs 1 species on the mainland Wallace came up with the same idea and they published together o Adaptations inherited characteristics of organisms that enhance survival and reproduction in specific environments o Natural selection process by which individuals that have traits that allow them to survive and reproduce at higher rates Underlying case of descent with modification o Artificial selection humans have manufactured species by breeding those with specific traits o Influences on Darwin Lamarck evolution occurs new species appear Lyell Uniformitarianism mechanisms of change are the same over time Enough time for biological change to occur Malthus we are going to outgrow our food supply Competition for resource Selective breeding plant animals saw how fast evolution o Observations Resources are limited Members of a population often vary in inherited traits All species can reproduce more than what their environment can support and many fail to survive and reproduce o Inferences Individuals whose traits give them a higher probability of surviving and reproducing in a given environment tend to have more offspring than other individuals This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in a population over generations o Natural selection requires variability o Favorable traits vary with environment no perfect variation Support for evolution Evolution doesn t create changes changes occur and natural selection selects those that are most favorable Relies on local environment Homology underlying similarities yet differing functions among organisms indicating a common ancestor o Analogy similar functions but different ancestry Flight organs of a bug vs a bird o Homologous structures variations on a structural theme present in a common ancestor differences in the details Embryos all have tails and gill like structures Vertebral forelimb o Homologous genes also found The homeobox used in the body patterns of all animals Regulatory genes Vary in where and to what extent it is expressed o Vestigial structures features that are no longer used but were once used by ancestors Ear wiggling muscles in humans pelvis in whales At the molecular level DNA RNA Genetic code is universal Pseudogenes are like vestigial organs Embryology o Primitive ancestral structures seen in embryos that are not seen in later developmental stages o Phylotype state all vertebrate embryos have pharyngeal pouches gill slits that develop into other organs around the neck Humans have a tail that is lost at later stages Not the same as vestigial organs Suggests a common ancestor Evolutionary tree diagram that reflects the relationships among groups of organisms Convergent evolution when 2 species resemble one another but aren t related o Sugar glider vs flying squirrel Fossils preserved parts traces of plants or animals that were once alive o Provide a record of evolution appearances and disappearance and changes over time o Hardest parts most likely to be preserved o Footprints could show behavior o Amber preserves the actual tissue o Macro evolution Repeated branching speciation events adaptive radiations followed by selective survival and extinctions Horse evolution Went from a small delicate teethed shrub eating forest dweller with 4 toes to a hooved 1 toed grass eater o Teeth slowly got larger o Remnants of toes in skeleton o Larger body size Many horse like species in each layer only a few escaped extinction o Horses actually went extinct in north America and had to be reintroduced o Paleontology study of fossils o Age of fossils Relative dating stratigraphy Strata superimposed layers of rock The lower the strata the older the fossil Index fossils common forms mollusks arthropods common fossils usually found at the edge of the sea unique to a geologic period and worldwide in distribution o Used as markers o Need to apply dates through absolute dating Absolute dating radioactive decay We know the probability of decay and that the rates of decay cannot be influenced by ambient physical or chemical environments treatments Carbon 14 has a half life of 5730 years o Half life amount of time it takes for of the original amount to decay o Good for only organic materials not fossils because the fossils have been replaced by rock o Rate of 14C is not constant Calibrated against bristlecone pine wood samples Cannot test anything past the 50s Calculations Nt 1 T ln N0 o T age of specimen o decay constant 0 693 t1 2 o t1 2 half life of isotope o Nt amount of isotope at time T o N0 amount of isotope at T 0 Ex o Soapberry bugs beak lengths vary based on which fruit they eat Very speedy evolution o Drug resistant bacteria MRSA resistant to antibiotics Overuse of antibiotics Biogeography geographic distribution of species o Influenced by continental drift o Pangaea all land masses in one spot Explains distribution of fossils and descendants o Endemic when species are found nowhere else in the world Often on islands