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
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
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
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.