  It is the process through which the characteristics of organisms change over successive
   generations, by means of genetic variation and natural selection.
  Microevolution is defined as changes in gene frequency in a population from one generation to
   the next. A population is a group of organisms who interbreed with each other.
  Macroevolution is evolution on a big scale, the descent of many species from one common
   ancestor over billions of years.
Origin of Life                                            a "hot dilute soup". In this soup, organic
                                                          compounds, the building blocks of life,
  It is generally agreed that all life today             could have formed. This idea was called
   evolved by common descent from a single                biopoiesis
   primitive lifeform.
  All known organisms share certain general          Fundamental Properties of Life
   properties, and to a large degree these
   properties define what we mean by life.               Cellular organization : All organisms
                                                          consist of one or more cells—complex,
  Scientists Disagree about Where Life
                                                          organized assemblages of molecules
   Started : The atmosphere of the early
                                                          enclosed within membranes.
   earth was rich in hydrogen, providing a
   ready supply of energetic electrons with              Sensitivity : All organisms respond to
   which to build organic molecules.                      stimuli— though not always to the same
                                                          stimuli in the same ways.
  The      Miller-Urey      Experiment       :
   Experiments attempting to duplicate the               Growth : All living things assimilate
   conditions of early earth produce many of              energy and use it to grow, a process called
   the key molecules of living organisms.                 metabolism. Plants, algae, and some
                                                          bacteria use sunlight to create covalent
  Theories about the Origin of Cells : The
                                                          carbon-carbon bonds from CO2 and H2O
   first cells are thought to have arisen
                                                          through photosynthesis. This transfer of
   spontaneously, but there is little agreement
                                                          the energy in covalent bonds is essential to
   as to the mechanism.
                                                          all life on earth.
  The Earliest Cells : The earliest fossils
                                                         Development : Multicellular organisms
   are of bacteria too small to see with the
                                                          undergo systematic gene-directed changes
   unaided eye.
                                                          as they grow and mature.
  In 1924 when Alexander Oparin
                                                         Reproduction : All living things
   reasoned that atmospheric oxygen
                                                          reproduce, passing on traits from one
   prevented the synthesis of the organic
                                                          generation to the next. Although some
   molecules. Organic molecules are the
                                                          organisms live for a very long time, no
   necessary building blocks for the
                                                          organism lives forever, as far as we know.
   evolution of life. In his The Origin of
                                                          Because all organisms die, ongoing life is
   Life, Oparin argued that a "primeval soup"
                                                          impossible without reproduction.
   of organic molecules could be created in
   an oxygen-less atmosphere through the                 Regulation : All organisms have
   action of sunlight.                                    regulatory mechanisms that coordinate
                                                          internal processes.
  Around the same time J.B.S. Haldane
   also suggested that the Earth"s pre-biotic            Homeostasis : All living things maintain
   oceans, which were very different from                 relatively constant internal conditions,
   what oceans are now, would have formed                 different from their environment.