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Transcript
Chapter 7 Evolution and the Fossil Record 1 Chapter 7 - Guiding Questions • What lines of evidence convinced Charles Darwin that organic evolution produced the species of the modern world? • What are the components of natural selection? • What is the source of the variability that is the basis of natural selection? • What role does geography play in speciation? • What factors lead to evolutionary radiation? • Why is convergence one of the most convincing kinds of evidence that evolutionary changes are adaptive? • Why do species become extinct? • What is mass extinction? • In what ways can evolutionary trends develop? 2 Evolution Evolution – changes in populations, which consist of groups of individuals that live together and belong to the same species – a change in gene frequencies – populations evolve, not individuals • YOU can’t evolve! Extinct ground sloth (20 ft long) 3 Evolution Adaptations – specialized features of animals and plants (or any other organism) which perform one or more useful functions – allow that organism to excel in its environment – YOU can only modify characteristics over which your genes have control; e.g., tanning Cat skull Horse skull Venus Flytrap 4 Inefficient Evolution • can only operate by changing what is already present; • it’s the business of remodeling rather than new construction from scratch • e.g., to make a new structure, natural selection starts by modifying an already existing one – e.g., how could ‘night vision’ evolve? 5 Charles Darwin • 1831 – set sail on the Beagle – schooled in uniformitarianism • Lyell’s Principles of Geology – a keen observer of natural phenomena • 1859-On the Origin of Species by Natural Selection 6 Some of Darwin’s Observations • Rhea – large flightless birds – found only in South America – also found extinct, fossil forms • Some similarities but also obvious differences from ostrich (Africa) and emu (Australia) 7 More of Darwin’s Observations • sloths and extinct armadillos – unique to the Americas 8 More of Darwin’s Observations • Oceanic islands – many barren; Hawaii has no native snakes, frogs, FW fish, etc. – species must have originated elsewhere • Galápagos Islands – tortoises with shells unique on each island – shared a common ancestry – followed later by differentiation 9 Galapagos Islands Range from 3 to 5 my old 10 Galapagos Tortoises • 14 subspecies, 11 extant, several with very small populations – e.g., Lonesome George 11 Lonesome George Isla Pinta 12 Darwin’s Famous Finches • Finches of the Galápagos – different beak types • slender-insectivorous • sturdy-seed crushing • woodpecker-like-tool user – differentiation based on lifestyle – curiously resemble a South American mainland finch 13 Adaptive Radiation of Darwin’s Finches 14 Feeding Adaptations of Ground Finches 15 Charles Darwin • Additional observations – Anatomical relationships • embryos of many vertebrates are quite similar, even superficially indistinguishable 16 17 Charles Darwin • Additional observations – Anatomical relationships • embryos of many vertebrates quite similar • homology – presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions 18 19 Charles Darwin • Additional observations – Anatomical relationships • embryos of many vertebrates quite similar • homology – presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions • vestigial organs – organs that serve no apparent purpose but resemble organs that perform functions in other creatures 20 Pelvic structures in whales and snakes 21 Vestigial Structures 22 Theory of Evolution • Natural Selection- ‘survival of the fittest’ – the process that operates in nature but parallels the artificial selection by which breeders develop new varieties of plants and animals • success of an individual determined by advantages it has over others – survives to bear offspring with same trait 23 24 25 Antibiotic Resistant Bacteria 26 The Basis for Natural Selection • There is much variation between members of a species. 27 28 The Basis for Natural Selection 1. There is much variation between members of a species 2. Reproduction is way in excess of the number that the habitat can survive e.g., Robins 29 E.g., Robins 30 The Basis for Natural Selection 1. There is much variation between members of a species 2. Reproduction is way in excess of the number that the habitat can survive e.g., Robins 3. Differential reproductive success-those best adapted survive to reproduce the most 31 Will the all survive? 32 Theory of Evolution • Darwin didn’t have all the tools we have today to explain his idea. • Genetics was in its infancy—Mendel’s ideas, though contemporary with Darin, weren’t appreciated for decades. • Genes-hereditary factors • Particulate inheritance – Gregor Mendel’s idea that organisms retain identities through generations – Peas • No blending • Colors could be masked for generations 33 34 Theory of Evolution • Mutations – alteration of genes – provides for variability – very few are helpful • DNA – Deoxyribonucleic Acid – transmits chemically coded information – mostly found in chromosomes 35 36 Theory of Evolution • sexual recombination – each parent contributes one half of its chromosomes to offspring via a gamete • special reproductive cell containing one of each type of chromosome – female ovum/egg; male sperm – yields new combinations-e.g., my kids aren’t exact copies of me; genes of their mother and me are both present. • mutations increase variability—and we all have them! • gene pool – sum total of genetic components of a population or group of interbreeding individuals – you have only a small subset of the human gene pool • reproductive barriers limit the pool and keep species separate • speciation – origin of a new species from two or more individuals of a preexisting species 37 Reproductive Isolation Spring breeder Fall breeder 38 Origination • Evolutionary radiations – pattern of expansion from some ancestral adaptive condition represented by descendant taxa • adaptive breakthrough – appearance of key features that allow radiation to occur • fossil record documents patterns – E.g., Jurassic corals 39 Jurassic Corals 40 Origination • Rates of speciation – Galápagos Islands-formed millions of years ago – Lake Victoria • 13,000 years old • 497 unique species of cichlid fish, many with specialized adaptations • Molecular clock – assume average rate of mutation – determine pace of change – extrapolate timing of change 41 Convergence • Evolution of similar forms in two or more different biological groups • Marsupials and placental mammals – similar form – isolated, adaptive convergent evolution after initial divergence 42 • caused by extreme impacts of limiting factors Extinction – predation – disease – competition • pseudoextinction – species evolutionary line of descent continues but members are given a new name • high rates of extinction make useful index fossil – ammonoids 43 Extinction • rates – average rate has declined through time • mass extinctions – many extinctions within a brief interval of time – largest events peak at extinction of >40% genera – rapid increase (radiation) follows 44 Modern Mass Extinctions • fossil patterns reflected in modern – tropical species – large animals • loss of habitat • direct exploitation • likely replacement by opportunistic species 45 Evolutionary Trends • Cope’s rule – body size increases during evolution of a group of animals – structural limitations on size • specialized adaptations limit evolution – elephants – manatees 46 Evolutionary Trends Whales • terrestrial origin – 50 Ma – small (2 m) mammals with feet • marine adaptation – – – – 40 Ma lost hind limbs no pelvic bones up to 20 m 47 Phylogeny • Phylogeny – complex, large-scale trend within a branching tree of life – gradual large-scale change from one species to another is rare • e.g., Jurassic coiled oysters 48 Phylogeny • Axolotl – example of rapid speciation from parent species • parent is amphibious • offspring is aquatic throughout life after one simple genetic change 49 Phylogeny • rates • gradualistic model – very slow rates • punctuational model – rapid evolution with little change between steps – bowfin fish • little change in 60 m.y. 50 Phylogeny • Horses – increase in body size – evolved tall complex molars and single-hoofed toe – change driven by climate • expansion of grasslands • Dollo’s law – evolutionary transition from at least several genetic changes is highly unlikely to be reversed by subsequent evolution 51 52 53