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5.4 Evolution 5.4.1 Define evolution cumulative change in the heritable characteristics of a population. • ‘heritable’ – • changes must be passed on genetically from one generation to the next • implies that evolution doesn’t happen overnight • ‘cumulative’ • one change isn’t enough to have major impact on the species • ‘population’ • changes do not affect just one individual 5.4.1 Define evolution Five “sub theories” : Evolution: all life is and has been perpetually changing Common descent: if traced back far enough, all life has common ancestor Gradualism: evol change is slow & gradual Multiplication of species: speciation leads to diversity of life; pops adapt to locations, become reproductively isolated from other pops Natural selection: produce genetic variation & select for/against History of Evolutionary Thoughts Lamarck’s Theory of Evolution Jean-Baptiste Lamarck, 1809 one of first scientists to understand that change occurs over time stated that changes are adaptations to environment acquired in an organism’s lifetime said acquired changes were passed to offspring Lamarck’s Theory of Evolution Idea called Law of Use and Disuse If a body part were used, it got stronger If body part NOT used, it deteriorated Lamarck’s Theory of Evolution Inheritance of Acquired Characteristics proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime these traits could then be passed on to their offspring over time this led to new species Lamarck’s Theory of Evolution Lamarck’s Mistakes Lamarck did not know how traits were inherited (Traits are passed through genes !) genes are NOT changed by activities in life change through mutation occurs before an organism is born Charles Darwin 1809-1882 British naturalist In 1858, Darwin and Wallace independently proposed the idea of evolution by natural selection Charles Darwin Darwin published On the Origin of Species by Means of Natural Selection the following year Charles Darwin (1809-1882) 5.4.2 Outline evidence for evolution. Fossil record transition species Comparative Anatomy homologous & vestigial structures Comparative Embryology • embryonic development Molecular record protein & DNA sequence Artificial selection human-caused evolution Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time Fossil record Fossil record A record showing us that today’s organisms descended from ancestral species 550 500 Body size (kg) 450 Equus 400 350 300 250 Merychippus 200 Mesohippus Hyracotherium 150 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 Millions of years ago 5 0 Fossil record A record showing us that today’s organisms descended from ancestral species Fossil record Land Mammal ? ? ? ? Fossil record Fossil discovery of early tetrapod in 2006 (Tiktaalik) “missing link” from sea to land animals Comparative Anatomy Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor Comparative Anatomy Homologous structures similarities in characteristics resulting from common ancestry Results of adaptive radiation - emergence of many species from common ancestor All vertebrates have similar bone structures in their limbs Comparative Anatomy Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don’t be fooled by their looks! Comparative Anatomy Analogous structures Flight evolved in 3 separate animal groups evolved similar “solution” to similar “problems” may have developed as a result of convergent evolution – unrelated species share the same environment (similar environmental pressures) and independently evolve similar structures Comparative Anatomy Analogous structures Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related Those fins & tails & sleek bodies are analogous structures! Comparative Anatomy Homologous structures Analogous structures Results from: Results from: Adaptive radiation Convergent evolution Common ancestor Different ancestors Similar origin Different origin Different functions Similar functions Ex. wing of bat, human Ex. wings of bird, wings of arm, dolphin flipper insect Remember: Adaptive radiation Convergent evolution Comparative Anatomy Vestigial structures Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for noncritical structures without reducing fitness snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone, appendix Comparative Anatomy Vestigial structures PBS: Whales in the Making http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc. Molecular record DNA & proteins are a molecular record of evolutionary relationships Closely related species have sequences that are more similar than distantly related species Human/kangaroo 100 Human/ cow Dog/ cow Nucleotide substitutions 75 Rabbit/ rodent Human/rodent Llama/ cow Horse/ donkey 50 Horse/cow Sheep/ goat Pig/ cow 25 Goat/cow 0 0 25 50 75 Millions of years ago 100 125 Molecular record Human Macaque Dog Bird Frog Lamprey 32 45 67 125 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans Artificial selection (selective breeding) Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties” line of evidence that supports evolution by natural selection the breeding of domestic plants and animals to produce specific desirable traits (ex. different breeds of dogs) people are doing the “selecting” rather than the environment Artificial selection (selective breeding) 5.4.3 State that populations tend to produce more offspring than the environment can support. Natural populations (a population consists of all the individuals of one species in a particular area) of all organisms have the potential to increase rapidly – organisms produce far more offspring than can possibly survive 5.4.3 State that populations tend to produce more offspring than the environment can support. More than needed to keep species around More than K (carrying capacity) can support, but limited resources Intraspecific competition Some have competitive advantage such as traits, behaviors, symbiosis) More fit (competing for resources, fighting disease, etc.) = More likely to successfully reproduce Freq of these alleles higher in next generation 5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival. 5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival. • Some individuals selected FOR • Some selected AGAINST • Survivors (selected FOR) form new breeding population • Increases freq of advantageous alleles 5.4.5 State that the members of a species show variation. Individual members of a population differ from one another in their ability to obtain resources, withstand environmental extremes, escape predators etc. (Variation) 5.4.5 State that the members of a species show variation. At least some of the variation among individuals in traits that affect survival and reproduction is due to genetic differences that can be passed on from parent to offspring – natural selection Over many generations, differential, or unequal, reproduction among individuals with different genetic makeup changes the overall genetic composition of the population – evolution Evolution is the result of natural selection 5.4.6 Explain how sexual reproduction promotes variation in a species. 5.4.6 Explain how sexual reproduction promotes variation in a species. MIXING IT UP w/MEIOSIS! Random assortment of chromosomes in Metaphase I 2^n combinations of chroms in daughter cells 8,388,608 in humans!! Crossing-over in Prophase I New combos of alleles on a chromosomes Random fertilization any gamete can fertilize any gamete from the other individual Darwin’s Theory of Natural Selection: 1. Populations produce more offspring than can 2. 3. 4. 5. possibly survive. (overproduction) Individuals in a population vary extensively from each other, mostly due to inheritance. (variation) Struggle to survive: individuals whose inherited characteristics best fit to environment leave more offspring than less fit. (survival of the fittest) Unequal ability of individuals to survive and reproduce leads to gradual change in population. (adaptation) Favorable characteristics accumulate over generations – (descent with modification). 5.4.7 Explain how natural selection leads to evolution. 5.4.7 Explain how natural selection leads to evolution. Individuals with genetic characteristics that are WELL- adapted for environment Tend to be MORE successful at accessing resources And thus have BETTER chance of surviving to maturity Since they survive to adulthood, these successful organisms have a better chance to reproduce and pass on their genetic characteristics to the next generation. Over many generations, accumulation of changes in the heritable characteristics of a population results in evolution. THE GENE POOL HAS CHANGED! 5.4.8 Explain 2 examples of evolution in response to environmental change. (one must be antibiotic resistance in bacteria) 5.4.8 Explain 2 examples of evolution in response to environmental change. (one must be antibiotic resistance in bacteria) http://www.sumanasinc.com/scienceinfocus/sif_antibiotics.html 5.4.8 Explain 2 examples of evolution in response to environmental change – peppered moth melanism 5.4.8 Explain 2 examples of evolution in response to environmental change – peppered moth melanism 5.4.8 Explain 2 examples of evolution in response to environmental change – insecticide resistance Insecticide Resistance – evolution in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective