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The Theory of Evolution
What exactly is a theory?


A theory is a well tested concept that
explains a wide variety of observations.
A theory should be able to make
predictions about future observations.
What is Biological Evolution?
Biological evolution is the change that
species undergo over time. More
precisely, it is the change in the gene
pools of living populations of species
which occurs over time.
What exactly does theory of evolution
state?
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All life forms (species) have developed from other
species.
All living things are related to one another to
varying degrees through common decent (shared
common ancestors).
All life on Earth has a common origin. In other
words, that in the distant past, there once existed
an original life form that gave rise to all subsequent
life forms.
The process by which one species evolves into
another involves heritable genetic mutations.
How does Natural selection Work?

Any Species of
animals produces
more offspring then
the environment can
handle.
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There are individual differences among the
offspring (mutations).
Because too many offspring are in the
environment only some will survive.

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Those that possess traits to survive best
in the environment will survive.
Those that do not die pass on their
genetic code to their offspring.

In this way only the fittest of the species will
survive and through this process of Natural
Selection evolution or changes occur in the
species.
What is the Evidence for Evolution?
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Fossil Record
Biogeography
Comparative Anatomy
Comparative Embryology
Comparative Biochemistry
Fossil Record

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Organisms have
changed over time.
Some present species
are not present in the
fossil record
Some current species
are similar, but not
identical, to some
previous species.
Biogeography

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Organisms evolve to adapt to their
particular environment, then spread to
other locales.
Evidence comes from the distribution of
similar species found around the world
Biogeography
Comparative Anatomy

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Related organisms share a unity of body
plan.
The same body structures can perform
adaptive functions.
Among vertebrates, forelimbs have the
same set of bones.
Homologous Structures
Comparative Embryology

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Related organisms develop similarly.
Early embryos of all vertebrates are very
similar
Early development reflects evolutionary
origins
- “Ontogeny recapitulates phylogeny”
Do these look Similar?
Comparative Biochemistry

All living things use the same basic
biological molecules for similar functions.
- The nitrogen bases in all organism are the
same: A T G C.

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Metabolic systems are similar among
species.
- Photosynthesis, respiration, fermentation, etc.
Basic cell structure is almost universal.
Vestigial Organs

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Hunan appendix is useless yet in other
mammals, including primates, it is necessary to
aid in digestion of high cellulose diet.
Human external ear muscles still present but
useless.
Humans have tailbones and some babies are
occasionally born with tails.
Some snakes have skeletal limbs.
Misconceptions about Evolution

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Evolution only
progresses forward
Reality: There are
several species
including the crocodile
and the shark that
have remained
virtually unchanged
for millions of years

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Man evolved from
monkeys
Reality is that man is
on different branch of
the evolutionary tree
than monkeys.

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Evolution occurs in individuals
Reality is that evolution occurs in
populations.
There are no modern intermediate
species

Consider the
platypus! It is a
mammal that lays
eggs.
Different Model of Evolution

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Evolution always occurs very slowly
Reality: Punctuated evolution can occur
over a relatively short time.