AP Biology Chapter 15 Darwin and Evolution Darwin: a reluctant rebel

AP Biology Evolution explains the Diversity and Unity of life 1. Diversity – the abundance of different forms of living things on Earth 2. Unity – the biochemical, cellular, genetic, and physiological characteristics/processes common to all living things

AP Biology What is Evolution?  The change in a species over time (i.e. the gene pool changes due to adaptations) 1. The Process: Descent thru Modification  new life comes into existence over time  all species come from common ancestry  all species comes from existing species via modification

AP Biology History of Evolutionary Thought  Carolus Linnaeus ( )  Taxonomist  Binomial Nomenclature  Agreed with the “fixity of species” theory  However, he performed hybridization experiments which made him think a species might change with time

AP Biology LaMarck  Organisms adapted to their environments by acquiring traits  change in their life time  Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm  Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat  transmit acquired characteristics to next generation

AP Biology History of Evolutionary Thought  Alfred Wallace ( )  British naturalist  came up with the same theory as Darwin independently  Natural Selection (Survival of the Fittest)  Darwin’s and Wallace’s ideas were published at the same time  But Wallace did not have as much evidence as Darwin

AP Biology Charles Darwin   British naturalist  Proposed the idea of evolution by natural selection:  Organisms that are best fit for the environment, survive and reproduce (“survival of the fittest”)  Collected clear evidence to support his ideas

AP Biology LaMarckian vs. Darwinian view  LaMarck  in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring  Darwin  giraffes born with longer necks survive better & leave more offspring who inherit their long necks

AP Biology Robert Fitzroy Voyage of the HMS Beagle  Invited to travel around the world  (22 years old!)  makes many observations of nature  main mission of the Beagle was to chart South American coastline

AP Biology Voyage of the HMS Beagle  Stopped in Galapagos Islands  500 miles off coast of Ecuador

AP Biology Galapagos Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 500 miles west of mainland

AP Biology Finch?Sparrow? Woodpecker? Warbler? Darwin found… birds Finch?Sparrow? Woodpecker? Warbler? Collected many different birds on the Galapagos Islands. Thought he found very different kinds…

AP Biology Darwin was amazed to find out: All 14 species of birds were finches… Finch?Sparrow? Woodpecker? Warbler? Finch?Sparrow? Woodpecker? Warbler? But Darwin found… a lot of finches Large Ground Finch Small Ground Finch Warbler FinchVeg. Tree Finch But there is only one species of finch on the mainland! How did one species of finches become so many different species now?

AP Biology Tree Thinking Large-seed eater?Small-seed eater? Warbler?Leaf-browser? Large Ground Finch Small Ground Finch Warbler Finch Veg. Tree Finch Ancestral species Descendant species

AP Biology Correlation of species to food source Adaptive radiation Seed eaters Flower eaters Insect eaters Rapid speciation: new species filling new niches, because they inherited successful adaptations.

AP Biology Voyage: November 24, 1859, Darwin published “On the Origin of Species by Means of Natural Selection”

AP Biology Natural Selection: 4 steps 1. Natural Variation exists in nature 2. Competition - Organisms struggle for survival: more organisms are produced than the environment can support 3. Survival of the fittest: Only the best adapted survives. Adaptations are important 4. Organisms change over time in response to the environment: organisms change but they have a common descent – they have common ancestors

AP Biology Adaptations: inherited characteristics that allow individuals to “do better” in their environment. Adaptations increase their chance of survival and reproduction

AP Biology Types of Natural Selection a.Directional – a shift in the freq. of a trait in a particular direction  common in changing env’ts Ex. Horseracing: pick horses that can run fastest

AP Biology b. Stabilizing – selects for avg. pheno. and against extreme pheno.  common in stable, unchanging env’t

AP Biology c. Disruptive – selects for extreme pheno. and against avg. pheno. b/c subject to predation

AP Biology

This is not just a process of the past… It is all around us today Artificial selection

AP Biology Selective breeding

AP Biology Natural Selection vs. Artificial Selection  Artificial Selection: nature provides variation, and humans select variations that we find useful (domestic animals and crops)  Natural Selection: the environment is the selective force. Only those organisms that are well adapted will survive in the wild.

AP Biology Sexual Selection