Unit 7 Evolution Mallard Creek Biology Evolution theories
Unit 7: Evolution Mallard Creek Biology
Ø Evolution- theories about how life began and flourished on Earth. 1. Spontaneous Generation (abiogenesis)- the idea that living organisms came from nonliving substances v v v Frogs developed from falling drops of rain Mice arose from sweaty underwear and wheat Flies arose from decaying meat 2. Biogenesis- life only arises from living
Disproving Spontaneous Generation Ø Francesco Redi – Meat and maggots Ø Lazzaro Spallanzani – Broth in vacuum Ø Pasteur – Bacteria in broth
The Early Earth is thought to be 4. 6 billion years old. Earth was “melted” by some catastrophic event. Elements rearranged to make the layers of the earth. Ø Reducing atmosphere theory - An atmosphere of hydrogen, nitrogen, carbon dioxide and carbon monoxide formed. NO OXYGEN! Ø Earth cooled and constant rain fell on the planet. Ø Lightning striking the atmosphere and waters caused the formation of organic compounds. Ø Ø Ø
Miller and Urey’s Experiment Miller and Urey’s experiment (1953) was an attempt to demonstrate how organic molecules could have first appeared on early earth. They hypothesized that if the right materials were in the atmosphere, and they were struck by lightning, they might form organic compounds. 1. Simulation of a reducing atmosphere: Gas chamber containing a mixture of methane, ammonia, water and hydrogen. NO OXYGEN! 2. Liquid water. 3. Lightning strike simulated with an electric spark. 4. Amino acids began to form in a trap that caught water that dripped from the gas chamber. This represents the “primordial soup”.
The First Cells Ø The first cells were found in the primordial ocean Ø Primordial- existing at the very beginning Ø Three characteristics: Heterotrophic 2. Prokaryotic 3. Anaerobic 1.
Evolution of Eukaryotes Endosymbiotic Theory – Some prokaryotic cells that were autotrophic were taken in by heterotrophic cells, and they formed a mutualistic relationship. l These were the first cells with chloroplasts. l These cells produced oxygen for the atmosphere Ø Later, other cells took in prokaryotic cells that carried out respiration. These were the first cells with mitochondria. l At first these cells were anaerobic l Cells became aerobic when oxygen was in atmosphere Ø
Geologic Time Scale Ø Eras – Major divisions of earth history. Ø Identified by the types of life present. Ø The fossil record is highly incomplete – there a great number of “missing links”.
Life Begins… and Evolves Precambrian Era Longest era – makes up 7/8 of earth’s history. Ø First bacteria and eukaryotic cells appeared. Ø First photosynthetic organisms appeared – the oxygen they made was added to the atmosphere. Ø Paleozoic Era Ø Begins with Cambrian period – “Explosion of life”. First marine life Invertebrates Ø Fish appeared Ø First land plants and animals because of oxygen in atmosphere Ø Amphibians Ø Ends with “mass extinction” - 90% of all marine species and 70% of land species died out.
Mesozoic Era Ø “Age of the Reptiles” Ø Dinosaurs developed at the beginning, died out at the end. Ø Earliest birds and mammals Ø Conifers abundant, earliest flowering plants appeared. Cenozoic Era Ø Current era – shortest era so far. Ø Age of the mammals. Ø First placental mammalsrats, bats, cats, elephants, whales, humans Ø Large carnivores Ø Humans emerged from northern Africa.
Charles Darwin The “Father of Evolution”Darwin came up with theory of natural selection (NS is the mechanism for Evolution) Ø HMS Beagle Ø Galapagos Islands Ø Adaptations ~ inherited characteristics that enhance an organism’s chance of survival. Ø
Galapagos Turtles and Finches Darwin observed that the curve of the shell of turtles on the Galapagos was adapted to the type of vegetation on each island. Darwin observed that the beak of finches on each island were adapted to the food sources available on each island.
Natural Selection Ø The individual that is best adapted to its environment is most likely to survive, mate, and pass on its genes to offspring. Ø “Survival of the Fittest”
Types of Natural Selection Directional Natural Stabilizing Natural Selection Disruptive Natural Selection favors one extreme trait value over another. Selection favors the intermediate trait over the extreme traits. Selection favors both extremes over the intermediate trait. Example: Peppered moths Example: Baby birth weight Example: Galapagos finches
Different Theories How evolution occurred
Gradualism Ø States that evolution is a slow but continuous process. Ø Occurs as genetic mutations that are successful gradually change populations. Ø Problem: Would require lots of transitional fossils in a specific order. These are not in the fossil record.
Punctuated Equilibrium States that populations stay the same for long periods of time, then suddenly have a burst of changes. Ø Idea is that transitional fossils would be few and rare. Ø
Evidences for Evolution Ø 4 main evidences for evolution: 1. 2. 3. 4. Homologous structures Analogous Structures Embryology Biochemistry
Homologous Structures Ø Structures that are similar in composition, but have different functions. Identify the similarities between these appendages. Identify the different functions of these appendages.
Analogous Structures Ø Structures that have a different composition, but similar function.
Embryology is the study of embryonic development. Ø Idea is that similarities between embryos are indicators of how closely related organisms are. Ø
Biochemistry Current theories look at how close genetic codes are to each other. Ø The more similarities in the DNA of two organisms, the more closely related they are supposed to be. Ø Ø DNA → RNA → Amino acids → Protein
Speciation The formation of a new species. Ø Species ~ A group of organisms that can reproduce successfully and produce fertile offspring. Ø Process Ø l l l A population must diverge (disruptive selection) Geographic isolation must occur to maintain the divergence. Reproductive isolation must occur so that the groups are truly different species.
Geographic Isolation (Allopatry) Ø Members of a species are physically separated. Ø Adaptations to different environments lead to differences that prevent mating.
Geographic Isolation
Reproductive Isolation Ø Barriers that prevent two populations from exchanging genes. Ø Differences in mating rituals, incompatible genitalia, sterile offspring.
Mutations Changes in DNA are thought to be the driving force behind evolution. Ø Mutations increase genetic variation in a population. Ø Accumulation of beneficial mutations lead to new species. Ø
Adaptive Radiation The evolution of several different forms from a simpler ancestor. Ø Requires speciation and adaptation to different habitats. Ø Model: Darwin’s finches Ø l l Common finch ancestor from mainland found island in the Galapagos chain with many unoccupied niches. Speciation occurred as the finch offspring adapted to the new niches available. Many daughter species develop.
Adaptive Radiation
Phylogenetic Tree (Cladogram) Ø Shows the evolutionary relationships among organisms. Ø Each branch shows a point in divergent evolution.
Constructing a Cladogram Identify the organism in the table that is least closely related to the others. Ø Use the information in the table to construct a cladogram. Ø Organism Backbone Legs Hair Earthworm Absent Trout Present Absent Lizard Present Absent Human Present
Phylogenetic Tree
Primate Evolution Ø Ape to Man
Type of Selection? Different grass plants in a population range in length from 8 cm to 28 cm. The 8 -10 cm grass blades receive little sunlight, and the 25 -28 cm grass blades are eaten quickly by grazing animals.
Type of Selection? The spines of a sea urchin population vary in length. The short-spined sea urchins are camouflaged easily on the seafloor. However, long-spined sea urchins are well defended against predators.
Type of Selection? Members of a population of Amazon tree frogs hop from tree to tree searching for food in the rainforest. They vary in leg length. Events result in massive destruction of the forest’s trees. After several generations, only long-legged tree frogs remain alive.
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