Darwin’s Theory of Evolution Chapter 16

Section 16.1 Darwin’s Voyage Objectives: State Darwin’s contribution to science Describe the biodiversity Darwin observed Video clip

Evolution: Evolution: change in species over time Charles Darwin Born in England on Feb. 12, 1809 Naturalist who studied diversity of life Took 5 year trip on HMS Beagle (1831-36) HMS Beagle (captain and crew) would be mapping the coastline of S. America Evolution not just something that happened in the past Darwin’s ideas help to explain modern phenomenon like drug-resistant bacteria and newly emerging diseases like the avian or swine flues

Darwin’s Observations Species vary globally Different but ecologically similar animal species inhabited separated, but ecologically similar, habitats around the globe Also, noticed that kangaroos lived only in grasslands of Australia (not in similar grasslands of Europe) and rabbits that lived in grasslands of Europe were not found in grasslands of Australia – WHY?? Rhea S. America Ostrich Africa Emu Australia

Darwin’s Observations Species vary locally Hood Island Tortoise Different yet related species often occupied different habitats within a local area Tortoises of the Islands differed based on Island they were found on - Hood Island: tortoise has curved shell that is open near neck and legs to allow animal to reach the sparce, high vegetation - Isabela Island: tortoise has the dome shaped shell and short neck; vegetation is plentiful on this island Also observed several types of small brown birds on the islands with beaks of different shapes – thought they were wrens, warblers and blackbirds – all turned out to be finches found no where else (although related to species found in S. America) Isabela Island Tortoise

Darwin’s Observations Species vary over time Fossil: preserved remains or traces of ancient organisms Related?? Darwin also collected fossils on his journeys. He found a fossil of an organism called a glyptodont (long-extinct) in an area where armadillos currently live He wondered if the two might be related Looking at pictures – how are they the same? How are they different? On his way home, Darwin thought about what he had seen. He sent plant and animal species he collected out to experts for identification and discovered that many of the species he collected were related (several types of birds that he had observed turned out to be finches found no where else, although they resembled a S. American finch species) Began to wonder if different Galapagos species might have evolved from S. American ancestors

Check-in What is evolution? Contrast the pattern Darwin observed among the large, flightless birds and the pattern he observed among the tortoises. Change in species over time For the second question, have students write for 1 minute in response – then call on several students to share their responses Similar environments seem to result in similarities among organisms. Different environments result in differences among organisms.

Section 16.3 Darwin’s Ideas Objectives: Describe conditions under which natural selection occurs. Explain common descent.

Evolution by Natural Selection Struggle for Existence Not all young survive Some killed by disease, predators Only some reproduce Grasshoppers can lay over 200 eggs at a time. Only a small fraction of these offspring will survive to reproduce.

Evolution by Natural Selection Variation and Adaptation Natural differences among same species Adaptation: heritable variation that increases change of surviving and reproducing Variation in nature – green and yellow grasshoppers (color is a heritable trait) In this case, green is an adaptation because it allows the grasshoppers to blend into their environment and reduces the risk that they will be caught by predators.

Evolution by Natural Selection Survival of the fittest Fitness: how well an organism can survive and reproduce Organisms with favorable traits survive and reproduce Offspring inherit those traits/genes Green grasshoppers have a higher fitness than yellow grasshoppers because their green color allows them to hide better from predators. This means that green grasshoppers survive and reproduce more than yellow grasshoppers in this environment.

Evolution by Natural Selection Natural Selection occurs when More individuals are born than can survive There is natural heritable variation There is variable fitness among individuals More grasshoppers are born than can survive Individuals vary in color and color is a heritable trait Green individuals have a higher fitness in their current environment

Principle of Common Descent Descent with modification “All species – living and extinct – descended from ancient common ancestors” Darwin drew the first tree of life to describe how descent with modification could produce the diversity of life seen today. If you look back in time, you can find common ancestors shared by tigers, panthers, and cheetahs. Further back, you find ancestors that these felines (cats) shared with dogs. Further back, is the common ancestors of all mammals with birds, reptiles and fish. Further back still, are the common ancestors of all living things.

Check-in Describe the expected evolutionary change of these rabbits over time. Include the conditions under which natural selection occurs. Given two variations in rabbit fur color and the new environment (it is getting colder and so there is snow for a greater period of the year), what do you expect to occur. Be sure to describe HOW natural selection will work in this situation.

Section 16.4 Evidence of Evolution Objectives: Describe various types of evidence to support evolution.

Evidence of Evolution Biogeography Closely related but different Distantly related but similar Biogeography – study of where organisms live now and where they and their ancestors lived in the past Finches – populations on the islands evolved from mainland species (environments on the islands selected for closely related species) Similar habitats can produce species that have similar adaptations (environment selects for similar adaptations) even though they are distantly related (eg. similar ground dwelling birds inhabit similar grasslands in several different continents)

Evidence of Evolution Age of Earth Fossils Radioactive dating indicates Earth is about 4.5 billion years old Fossils Trace evolution of modern species from extinct ancestors In order for evolution to have occurred, the Earth must be very old.

Evidence of Evolution Anatomical Structures Homologous: similar structures inherited from common ancestor EX. Similar arm and hand bones in human, cat, whale, bat

Evidence of Evolution Anatomical Structures Analogous: similar function, but different structure (and different ancestor) EX. Wings of bird vs. wings of butterfly

Evidence of Evolution Anatomical Structures Vestigal: reduced in size and function EX. Pelvic bones in whale; appendix in humans

Evidence of Evolution Embryology Similarities in fetal development Early development of vertebrates is very similar which suggests that they have a common ancestor

Evidence of Evolution Biochemistry / DNA Similar DNA patterns 98% similarity between humans and chimps 90% similarity between human and mouse Similarities in the chemical compounds that make up organisms Ex. Cytochrome C used in cellular respiration is similar in almost all living cells

Check-in List some things that provide evidence to support the theory of evolution. Give an example of biogeography in which species are closely related but different. Biogeography, age of Earth, fossils, anatomical structures, embryology, biochemistry/DNA Finches, tortoises

Check-in What type of structure is each of the following an example of: Wings of bird and wings of bee Human appendix Wing of chicken and foreleg of alligator Analogous structure Vestigal structure Homologous structure

References DNA similarity: http://nature.ca/genome/03/c/20/03c_21_e.cfm