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Chapters 13, 14, & 15
 Earth has millions of other kinds of organisms of every
imaginable shape, size, and habitat.
 The variety of living things is called biological diversity.
 How did all these different organisms arise?
 How are they all related?
Evolution= The Tree of Life
 All living things share a common
 We can draw a Tree of Life to
show how every species is
 Evolution: Change over time; the
process by which modern species
have descended from ancient
species (common ancestors).
Evolution… theory or fact?
 It’s both!
 The theory of evolution is an explanation of HOW
evolution happens. Our understanding of this process
is always changing.
 Evolution is also a fact due to the huge amount of
indisputable evidence for its occurrence.
 Lamarck believed genes were
determined by the environment,
and the use or disuse of body parts.
 He thought that if an animal
acquired a characteristic during its
lifetime, it could pass it onto its
offspring (Inheritance of acquired
 Hence giraffes got their long necks
through generations of straining to
reach high branches.
Jean Baptiste de Lamarck
Charles Darwin
 A young, British naturalist interested in biological
diversity and how it occurred.
 Toured the world from 1831-1836 on board the HMS
 Took lengthy observations of the different species found
on the Galapagos Islands. Mainly of the different beaks of
finches, and shapes of tortoise shells found on various
 Published a book on his findings in 1859: The Origin of
Species by means of Natural Selection.
Natural Selection
 The best adapted to the environment survives to
 Proposed by Charles Darwin as the driving force
behind the theory of evolution.
Evolution by Natural Selection
 Natural selection occurs under 5 main conditions
 (1) Variation: Natural differences within a species
caused by mutations, and sexual reproduction.
 Adaptation: A variation that increases an organism’s ability
to survive and reproduce.
 Ex: Organisms of the same species that are faster, have bigger
claws, or are better camouflaged are likely to survive longer.
Natural selection continued…
 (2) The struggle for existence- Members of a population
must compete for food, space, and other limited
necessities of life; (3) competition.
 (4) Overproduction: Too many offspring, must compete,
some survive.
 (5) Survival of the fittest- Those most genetically “fit”
 Caused by variation + overproduction + competition + the
struggle for existence
Darwin’s Conclusions:
 1. The diverse forms of life have arisen by descent with
modification from ancestral species.
 2. The mechanism of modification has been natural
selection working over enormous spans of time.
A summary of Natural
 Only well-adapted individuals survive and reproduce.
From generation to generation, populations continue to
change as they become better adapted, or as their
environment changes.
 Darwin also proposed that, over many generations,
adaptations could cause successful species to evolve
into a new species.
 Speciation: The formation of a new species.