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Evolution
• Evolution is the idea that living species are
descendants of ancestral species that were
different from present-day ones
• Evolution describes the genetic changes
(mutations) in an organism over time
Evolution
• Organisms are adapted to their environment
• As descendants of a remote ancestor spread
into various habitats over millions and millions of
years, they accumulate diverse modifications
(adaptations) that fit them to specific ways of life
Evolution
• Natural variation among individuals is based on
heredity (and mutation). These variations enable
organisms to become adapted to their
environment over time
Natural Selection
• Natural selection is the process by which
favorable, inherited traits become more
numerous in future generations of a population
of reproducing organisms
• Over time, natural selection leads to species that
are well adapted (highly evolved) to their
environments
Natural Selection
• The concept of natural
selection was developed
by Charles Darwin; a
naturalist who sailed
around the world and noted
the unique adaptations of
animals in many diverse
environments (most
notably the Galapagos
Islands)
The Principles of Natural Selection
• Variation
– Some individuals, due to heredity or mutation,
possess characteristics which make them
better adapted to their environment
The Principles of Natural Selection
• Inheritance of Traits
– Best-suited organisms will survive to produce
more individuals that share same adaptation
The Principles of Natural Selection
• Struggle for existence/Competition
– More offspring are produced than can be
supported by resources
King Penguin Rookery © Momatiuk - Eastcott/Corbis
“Survival of the Fittest”
• Organisms are adapted to their environment
through natural selection
1 Population with varied inherited traits
2 Elimination of individuals with certain traits
3 Reproduction of survivors
Certain
individuals with
one particular
inherited trait will
be eliminated,
while others with
a different
inherited trait will
avoid elimination
Let’s look at an example…
Normal
allele;
vulnerable
to
pesticides
‘Resistant’ allele
passed to next
generation
Survivors
Alternate
allele;
resistant to
pesticides
Mechanisms of Evolution
• Evolution is dependent on genetics
• Reproductive component – organisms must
reproduce
• Heredity component – offspring must resemble
parents (traits passed on to offspring)
• Variation component – there must be genetic
variation among individuals of population
– genetic variation leads to variation in fitness
(the ability to survive and reproduce)
Evolution
• Remember, evolution is the genetic change in
populations over time
• Individuals do NOT evolve; evolution refers to
generation-to-generation changes
• Evolution does not lead to perfectly-adapted
organisms; natural selection results from
environmental factors that vary from place to
place and from time to time (a trait that is
favorable in one situation may be detrimental in
another)
Evolution
• Evolution is a gradual change over time
Evidence for Evolution
• Fossils!!! – the fossil record (the sequence in
which fossils appear in layers of sedimentary
rocks) provide some of the strongest evidence of
evolution
• Sedimentary rocks form from sand and mud that
settles to the bottom of seas, lakes and swamps;
when organisms die, they settle along with the
sediments and are preserved as fossils
Evidence for Evolution
Allosaurus: 65 mya
Seed fern: 150 mya
Trilobite: 230 mya
Artificial Selection
• Artificial selection – the process by which humans
have modified other species by selectively breeding
for desired traits
• All dogs are domesticated breeds of the Gray wolf,
Canis lupus
Evidence for Evolution
• Homologous structures – similar characteristics
that result from a common ancestry
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Developmental similarities reflect descent
from a common ancestor
Evidence for Evolution
• A prime (and very
amusing) example of
homologous structures
are vestigial organs;
remnants of structures
that have no apparent
function, but served
important functions in
organism’s ancestors
Evidence for Evolution
• A good example
of homologous
structures are
vestigial
organs;
remnants of
structures that
have no
apparent
function, but
served important
functions in
organism’s
ancestors
Evidence for Evolution
Vestigial structures of a whale
Evidence for Evolution
• In contrast to homologous structures,
analogous structures also provide evidence for
evolution
• Analogous structures are structures that share
functional similarities, not due to common
ancestry
• Analogous structures arise among unrelated
organisms in response to similar needs or
similar environmental factors
Analogous Structures
Examples:
wings of insects
and birds;
flippers of seals
and penguins
Evidence for Evolution
• Remember, evolution uses the materials and
processes that are already available (it fashions
adaptations, rather than starting from scratch)
• Evolution is a tinkerer, not a master engineer (a
tinkerer uses tools already there to improve)
• Adaptations are not perfect
• Evolution is constant; traits that are helpful for
adaptation today may not be so helpful in the
future
Evidence for Natural Selection
• Darwin’s fishes of the Galapagos Islands
14 species of finch;
1 common ancestor
(from the mainland);
different beaks
Mutations and sexual reproduction are the
driving forces of evolution
• New alleles originate by mutation, a change in
the nucleotide sequence of DNA
• Only mutations in cells that produce gametes
can be passed along to offspring
• Most mutations are harmful, however a mutant
allele may improve the adaptation of an
individual to its environment and enhance its
reproductive success
Mutations and sexual reproduction are the
driving forces of evolution
• Spontaneous mutation rates in animals and
plants average ~1 in every 100,000 genes per
generation (a slow process)
• Sexual reproduction provides a means of
increasing genetic diversity and variation,
creating genetically-distinct individuals with new
combinations of alleles (which may enhance
adaptation and reproductive success)
Evolution
• Evolution is a widely accepted scientific theory
that describes the observed changes in living
things over time
• Scientists use evolution to explain the great
diversity of life, but some dispute its ability to
describe the origins of life on Earth
Other theories out there
Name
Descent with modification?
Creation (A)
No
No
Transformism (B) Yes
Evolution (C)
Common ancestor?
No
Yes
Extinction?
No
No
Yes
Yes
extinction
(A)
change
(B)
change
(C)
change
Evolution
• Remember, evolution is an accepted (and wellsupported) scientific theory
• Scientific theories can never be proven (you
cannot prove a hypothesis) but can be
supported or rejected; must also be testable and
falsifiable