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Winston Churchill Vioxx Conspiracy, and dirty little secrets “Scientific facts” don’t always give us clear answers to important questions. Who decides what to do with “scientific facts”? What is “life” or “living” Something that has order ? What is “life” or “living” Something that has order ? What is “life” or “living” Something that reproduces ? What is “life” or “living” Something that reproduces ? What is “life” or “living” Something that grows and develops ? What is “life” or “living” Something that utilizes energy ? 3Fe + 4H2O <-===-> Fe3O4 + 4H2 Iron water iron (II,III) oxide hydrogen What is “life” or “living” Something that responds to the environment ? What is “life” or “living” Maintains status quo (homeostasis)? Farmer fixing his fence (life) vs Buffered lake (non-living) Definition of life: “I can not define it, but I’ll know it when I see it” -Supreme Court Justice Stewart Life on Mars? Life on Mars? Martian romantics Life on Mars? Happy face! Life on Mars? Life in extreme Earth environments A novel thermophile isolated from >300°C, 1500m deep, geothermal water pool Bacillus living at 55°C (131°F) Life on Mars fossils ? From Martian meteroite Bacteria (on Earth) Size: 1 µm vs 0.1 µm Are Martian fossils biological ? Martian fossils: -Too small? -biological? acid etches Definition of life: “I can not define it, but I’ll know it when I see it” -Supreme Court Justice Stewart Maybe not so easy after all! Symptoms of life: Order, reproduction, growth, development, energy utilization, response to environment But what distinguishes “life” from non-living chemical reactions? The physical properties of living things can change, and these changes can be inherited by offspring The physical properties of living things can change, and these changes can be inherited by offspring This is possible because the physical properties of “life” are determined by a program. This program can be copied, and when it is copied, it can be changed (mutated) The physical properties of living things can change, and these changes can be inherited by offspring This is possible because the physical properties of “life” are determined by a program. This program can be copied, and when it is copied, it can be changed (mutated) Life is unique because it is a set of chemical reactions that can EVOLVE So, we know what makes “life” unique But there are still many questions about how all the diversity of life came to be… Life is different from “non-living” things because life can Evolve Evolution inevitably results in Natural Selection and Descent with Modification. What’s that, and what’s the result? Natural selection 1. The members of a population have heritable variations. 2. The population produces more offspring than the resources of an environment can support. 3. There is competition for resources; as a result, the better adapted individuals survive and reproduce more than the poorly adapted. 4. Across generations, a larger proportion of the population becomes adapted to the environment. Natural Selection leads to Descent with Modification Once you have life, and competition for resources, natural selection will lead a population to change over time. Birds. Fig 1.11, page 9 Dogs (artificial selection) Descent with modification can lead to new species How much of life’s diversity can be explained by descent with modification? How many different times was life created from non-life in order to get all this diversity? All modern life on Earth is related by descent from a common ancestor (evolution). Why do we believe this? Same 4 nucleotides in DNA Same central dogma Same 20 amino acids in protein Because all life is descendent from one original life-form through an evolutionary process, we can work backward through time to modern life’s earlier and more simple form. All life descended from one common ancestor Figure 1.4, page 6. Three main branches (Domains) When did this occur? And how do they know that? Stromatolites: like microfossils of early life Modern stromatolites Ancient fossils (?) How old is the oldest fossil? Tape measure: 25 feet = 2.5 billion years 1 foot = 0.1 billion = 100 million years 1 inch ~ 10 million years 1/8 of inch ~ 1 million years width of hair (~1/1000 inch) = 10,000 years When did all this happen? And what does it mean? Earth forms Carbon isotope (first evidence of life) First fossil microbes Oldest eukaryotic fossil Animal diversity begins Period of heavy bombardment 4 dinosaurs hominids Oxygen accumulates in atmosphere 3 2 Time - billions of years ago 1 today When did all this happen? Geological timeline Billion years ago 15 4.5 4.0 3.85 2.0 0.5 0.05 0.005 0.0001 0.00001 0.000005 0.0000005 0.00000005 What was happening universe formed in Big Bang Earth formed Heavy bombardment stops Fossils evidence of life (?) Fossils of eukaryotes (?) multi-cellular life becomes abundant dinosaurs go extinct chimp/human diverge firs modern humans humans colonize Americas (Indians) ancient Egypt, Greece, Rome, etc dark ages of Europe your parents were born Life started quickly (~200 my), but intelligent life came so late it might have missed the party all-together (human intelligence arrived after 4 by of evolution, with only another 1 or 2 by left before all life on Earth ends)