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Evoluzione:
i concetti
chiave
The Origin of Species
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Evolution is the explanation for life’s unity
and diversity
Natural selection is the mechanism
3 inferences based on 5 basic observations
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Too many individuals for limited resources
Those with better traits survive and reproduce
Their traits dominate in population and cause it
to evolve
Too many individuals for limited
resources
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In populations, more individuals are born
than can be supported by the environment
Only a fraction will survive to the next
generation (there is a struggle for existence)
Observation 1
Fig 22.8
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Species have great
powers of potential
reproduction
Populations would
increase exponentially
if all individuals
survived and
reproduced
Observation 2
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But populations tend
to remain stable over
time, except for
seasonal fluctuations
Fig 52.17 Moose population
on island in Lake Superior
Observation 3
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Environmental
resources are limited
Discussion in Malthus,
“Essay on the Principle
of Population” helped
clarify this
~ Fig 52.19 Lucky Lynx
and its 1 hare
Those with better traits survive
and reproduce
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Struggle for existence is not random
Depends on an organism’s characters that
are, at least in part, hereditary
More fit individuals will leave more
offspring than less fit individuals
Observation 4
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Individuals in
a population
vary
extensively
Fig 22.9
Observation 5
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Much of this variation
is heritable
However, Darwin did
not know the
mechanism
Fig 1.3b
Their traits dominate in a population
and cause it to evolve
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Unequal ability of individuals to survive
and reproduce leads to gradual change in a
population
More favorable characters accumulate microevolution!
Peter and Rosemary
Grant have been
working on
Galapagos finches
since 1973 on Isla
Daphne Major.
Geospiza fortis is a
seed-eater that cracks
seeds by grasping at
the base of the bill
and applying force.
Beak size is
correlated with
consumed seed size.
Are characteristics variable in a population? YES.
Is some of the variation among individuals heritable? YES.
Is there an excess of offspring such that only some
individuals survive to reproduce? YES.
Is survival and reproduction nonrandom? YES.
Other Evidence for Evolution
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Organisms are
adapted to their
environments
Fig 22.10a A floral mantid on a
flower. Please look at the entire
figure in the text
Other evidence
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Artificial selection
Fig 22.11b Vegetables selected
by humans from wild “kole”
Other evidence
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Examples of natural
selection
Fig 22.12 Evolution of resistance to
insecticides in insect populations
Other evidence
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Homologous
structures
Fig 22.14 Forearm bones in mammals
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Other
evidence
Molecular “record” –
molecular homologies
Fig 17.16 Ribosomal structure (large
subunit of bacterial ribosome)
Other evidence
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Biogeography
Fig 34.32 Adaptive radiation of
Australian marsupials compared to
similarities among other mammals
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Other evidence
Fossil record
Fig 22.7 Elephant evolution based on fossils
Fossil Trilobites
Transitional fossils
Microevolution - generational changes in the
characteristics of a population
Macroevolution - origin of new species and
other taxonomic groups due to
accumulation of change over long periods
of time.
L’evoluzione ha la VISTA lunga…
Le forze motrici dell’evoluzione:
V
I
S
T
A
variation (variazione)
inheritance (ereditarieta’)
selection (selezione)
time (tempo)
adaptation (adattamento)