IB Biology-Chapter 5-Evolution and Biodiversity

Evidence for Evolution Darwin and Wallace @ age 22 Darwin sailed the HMS Beagle (1831)-for 5 years Alfred Russel Wallace independently developed a similar theory They presented ideas to Linnaean Society (1858)

Process of_________________________________ Heritable implies it’s not necessarily fast Cumulative implies that 1 change is not usually enough to have a major impact on species Process of cumulative change in the heritable characteristics of a population

Population-tells us it does not just affect 1 individual Speciation can arise if enough changes occur in a population- because the members of the new population do not have enough from pre-existing population to interbreed-rarely observable during human lifetime All life on earth unified by common origins Neo-Darwinism (modern synthesis)-how DNA shows evidence for evolution by natural selection more than any evidence thus far

The fossil record and evolution It is impossible to go back in time-thousands or millions of years ago and come up w/all the possible fossil evidence Fossils-petrified remains/traces of animals and plants-been collected for ~ 2 centuries Fossil record=accumulation of evidence from fossils

Convincing evidence compiled by paleontologists: Life that existed > 500 mya greatly different than today While earth has had oceans most of its existence, fish fossils have only been found in rocks 500 my old or younger (< 15% of the 3.5 billion y existence of life on earth Although most top predators today are mammal-e.g. Bears, orcas, big cats, and wolves, none were here @ time of dinosaurs or before Apart from organisms such as certain sharks, cockroaches, and ferns, most organisms present today have no similar form in fossil record Life on earth appears to constantly be changing, but most changes are over 100’s, thousands, or millions of years

Aging fossils By examining the differences in ratios of isotopes E.g. A fossil of higher amt C-14 is younger than one w/less C-14 C-14(14C)-slowly loses radioactivity to become N-14---- Decay=process of radioactive parent isotope changing into stable daughter isotope Half-life-speed by which this decay happens-_________________ time it takes ½ parent isotope to decay into stable daughter isotope

14C half-life=__________-so, when an animal dies, their bones will have lost ½ their14C after 5730 yrs./after 11,460 yrs. ½ of that (25% original) will be decayed So-looking ratio of radioactive C-14 to stable N-14, you can determine age of fossil—If there is 12.5 of radioactive isotope and 87.5 of stable,3 half-lives have passed (17,190 yrs.) After a certain # of half-lives, there are so few 14C atoms that it’s difficult to determine age accurately 5730 yrs

There are other isotopes w/longer half-lives, such as K-40 There are other isotopes w/longer half-lives, such as K-40. When minerals in rocks crystalize from magma, they contain a % K-40-Once they have hardened and crystallized, no more K-40 can be Added-However the # reduces as the isotope decays into more stable forms-used to determine age of rocks having formed from magma or lava between 100,000 yrs-4.6 billion years ago

Artificial selection and evolution Fossil record far from complete, but we have a good record of changes in heritable characteristics from science of breeding domesticated animals After practicing selective breeding for dozens and sometimes hundreds of generations, farmers and breeders realized that certain varieties of animals now had unique combinations of characteristics that did not exist before-evolution as a result of an accumulation of sm changes over time-_______________ ∴ this is artificial selection = people choose the traits to be reproduced—not a driving force in evolution of natural ecosystems by human choice

Evolution of homologous structures by adaptive radiation __________________________-similar in form but found in SEEMINGLY different species-as evidence of evolution E.g.- pentadactyl limbs in humans, bats and whales-shape and # bones may vary, general format the same, even though they may have different functions Darwin explained homologous structures were evidence of common ancestors Whales should be able to swim fine whether or not they have 5 phalanges-indicating more the reasoning behind common ancestry Homologous anatomical structures

Species divergence speciation ________________-process of an evolving population changing significantly enough so that the production of offspring w/ original population becomes impossible—i.e. 2 pop’s of a species have diverged(separated) and new species evolves from old one-both species continuing on separate ways speciation

Adaptive radiation Occurs when many similar but distinct species evolve relatively rapidly from a single or sm # species Happens when variations w/in a population allow certain members to exploit a slightly different niche in a more successful way By natural selection and the presence of some kind of barrier (such as water or a mt range), a new species can evolve

E.g.-primates of Madagascar and Comoro Islands-off SE coast of Africa.MYA, w/o competition from other primates, lemurs were prolific- large # offspring meant a greater chance for diversity Among the range of variation in Lemur species-some are better adapted to trees and some to the ground-and some to the desert Some are nocturnal while most are diurnal There are so many species due to _______________ Not a single species found anywhere else in world, yet fossils have been found on coast of Africa, Europe, and Asia It is believed lemurs were not successful in competing w/apes and monkeys-since as soon as traces of the other primates started to become prevalent in the fossil record, the lemur –like organisms became rare adaptive radiation

This would explain why continents and islands tend to have either prosimians or anthropoids-but not both Dozens of species have become extinct recently-esp. because of human anthropoids

Darwin’s finches of Galapagos Islands and Hawaiian Honeycreepers

Continuous variation and the concept of gradual divergence In the diagram (phylogenetic tree) above-species A, B, C, D came from a common ancestor-If any 2 tried to mate-they would not produce fertile offspring The above picture show how one species can have various splits over time-creating more diversity among species Sometimes branches on phylogenetic tree are so far apart that the species no longer physically resemble each other (eg-Darwin’s finches)-yet many species can spread over a wide geographical area

Eg-NOS-p.225 saltmarsh grass—species that has a wide geographical distribution, there can be measureable differences in DNA-because the climate and soil are different in different locations-∴ the pop’s adapt to the conditions available to them-and some versions of genes will be selected for and others will be selected against, so that the pop’s are best adapted to their areas=___________(any phenomena which alters the behavior and fitness of living organisms within a given environment) If this continues to produce genetic differences over a long enough time, it is not difficult to imagine a point @ which the differences are so separated that they become different species There comes a tipping pt beyond which differences outweigh similarities and can no longer freely reproduce selective pressure

Transient morphism---w/in a pop-there is often more than 1 common form Polymorphisms-different versions of a species - (different shapes-) can be result of mutation E.g.-Bison betularia-peppered moth-can have a peppered(grey) form or a melanic(black) form-melanic is a rare mutation that usually affects <1% of a population Grey form well camouflaged against light-colored surfaces, such as tree branches covered w/lichens The melanin(bulk) form is easily preyed upon by birds against light lichens From ~ 1860 a phenomenon was underway that cont’d for more than a century- Melanic form(carbonaria) was increasing in #’s Lichens sensitive to air pollution-industrial revolution producing SO2, which kill lichens-also a lot of blk soot Result was lichen –free, soot –darkened branches-more difficult for light – colored moths to survive predation Near industrial areas, the carbonaria were 95-100% of all the peppered moths @ present carbonaria rarely go above 30%-often 0%(improvement in air quality-UK Clean Air Act of 1956) Transient polymorphisms—changes from light –to dark-and back to light