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Transcript
Defining Life What is life? Evolutionary adaptation and evolution, natural selection Phylogenetic tree Metabolism Defining life 1. 2. 3. 4. 5. 6. Order Reproduction Growth and development Energy utilization Responsiveness to environment Evolutionary adaptation 1. Order ! Molecules in living organisms exhibit order. ◦ Arranged in patterns that make cell structures ! The presence of order in living organisms is a necessary, but not a sufficient condition for life. 2. Reproduction ! Living organisms reproduce or are products of reproduction. ◦ All organisms have finite lifetimes and eventually die. Reproduction corrects for this. ! Types of reproduction organism ◦ Between human beings - sexual ◦ Bacteria reproduce by cell division – asexual ! Exceptions: ◦ Mule is sterile and cannot reproduce even though it is a reproduction between a horse and a donkey ◦ Viruses are incapable of reproducing by themselves, need a living organism ◦ Prions are infectious proteins (mad cow disease) Amoeba – single cell 3. Growth and development ! Living organisms grow and develop in patterns in part by heredity, traits passed to an organism from its parents 4. Energy utilization ! Energy utilization in living organisms is one of the most basic requirements of life, without which organisms could not maintain order, growth and reproduction. 5. Responsiveness to environment ! Life interacts with the surroundings and responds to environmental changes ◦ Exception: human-made devices (thermostats) 6. Evolutionary adaptation ! Life evolves as a result of the interactions between organisms and the environment, leading over time to evolutionary adaptations that make species better suited for the environment ◦ When the adaptations are significant, these organisms may be very different from their ancestors – they may constitute a new species Evolutionary adaptation ! Species: groups of organisms that are genetically distinct ◦ Precise border between species not always clear (especially in e.g., microorganisms) ! Once a species is identified it is given a name consisting of two parts: Genus (generic) and Species (specific) ◦ Homo Sapiens, Homo Neanderthalensis ◦ Horses and donkeys: Equus Caballus and Equus Asinus Of the six basic properties of life, biologists consider the most fundamental to be evolutionary adaptation. Evolution is an ancient idea ! Anaximander (610-547 BC): life arose in water and evolved in more complex forms ! Empedocles (429-432 BC): creatures poorly adapted will die ! Jean Baptiste Lamark (early 1800s): relationship between fossils and living organisms. ◦ Life forms evolved by gradually adapting to perform successfully in their environment; not able to explain how evolution worked ! Charles Darwin: The origin of species, 1859 Darwin’s The origin of species: Overproduction and competition for survival 1. ◦ 2. Population has potential to produce more offspring than the environment can support (food, shelter) => competition for survival Individual variations ◦ Individuals vary in many heritable traits, some traits make them better to compete for survival Conclusion: Unequal reproductive success = natural selection Individuals whose traits best enable them to survive and reproduce will (on average) leave the largest number of offspring that in turn survive to reproduce Evidence for evolution by natural selection: Darwin backed up his claim by documenting cases of related organisms adapted to different environments of lifestyle. The different species of finches from Galapagos evidence of Darwin’s theory of natural selection because they have evolved adaptations from a common ancestor to suit the environmental conditions on different islands. ! Darwin discovered fossils of extinct organisms related to modern organisms (giant armadillos) ! Realized that natural selection explains differences not only between closely related modern species (finches), but larger changes can occur over a long time => extinction of some species and appearance of others. ! Artificial selection: selective breeding of domesticated plants and animals by humans over few thousands of years ◦ Dog breeds with common ancestors: Rottweilers and Chihuahuas ! Evolutionary adaptations are related to changes that occur through time in DNA ! Most basic definition of life which takes accounts of the relative importance of the six fundamental properties of living things is that life is something that can reproduce and evolve through natural selection. ! http://www.nasa.gov/vision/universe/starsgalaxies/ life's_working_definition.html ! Above link nice reading about whether it is suitable to define life at all – general theory of living systems may be more useful ◦ Doesn’t yet exist ! Brings us to the question: Do we need to define life in order to detect it? ! Life may not be definable but there are characteristics of life that might be canonical of all life and they would leave “biosignatures” . ◦ Carbon‐based ◦ Self‐replicating ◦ Uses chemical and light energy ◦ Undergoes Darwinian evolution ◦ Requires water and more than 20 elements All studies on the origin of life rely on these characteristics as the basic starting points. Which of these characteristics of Earth life has the largest likelihood of being different in extra-terrestrial carbon-based life? ! Commonly believed that life can be recognized even if it is very different from life as we know it ◦ Life can be recognized by what it does: living organisms create hallmark molecules and create chemical disequilibrium (Nealson, University of Southern California) ! The Earth-centric approach to search for life on other planetary bodies: ◦ Follow the water, follow the energy, etc. ◦ Look for biosignatures: " Organic compounds that follow the rules of C chemistry found only in organisms (living or fossils) " Ratios of CHON indicating life (‘redfield ratios’) " Isotopic fraction of C,S, N indicating metabolism ◦ Look for intact ‘cells’ enclosed in a membrane Earth-centric approach expressed in media… “The astounding March 11 discovery made at the Ross‐Waterhaus Observatory in Johannesburg, South Africa comes just weeks after University of Arizona scientists announced their findings that a huge flood swamped the Red Planet in ancient times. At least one expert believes this proves that the Noah story is true – only it didn’t happen on Earth.The tale of Noah may have been brought to Earth by Martian visitors in prehistoric times” What about ‘weird’ life (different from Earth life), could we detect it? ! Weird life can be either modifications of Earth’s carbon based life or life that exists out of the habitability conditions on Earth (we are not sure about the full limits of C based life) ◦ Slightly weird: Same biochemistry but different amino acids; novel metabolisms; different genetic code ◦ A bit more weird: Same biochemistry but utilizing novel energy sources other than light or chemical energy ◦ Even more weird: different biochemistry, not-protein catalysis; C based but in non-water solutions; Si based life ◦ Very weird: non-cellular life