Transcript Chapter 13 - Evolution

Evolution
• Evolution is descent with modification; the
idea that living species are descendents of
ancestral species that were different from
present-day ones
• Evolution describes the genetic changes in a
population over time
Evolution
• Organisms are adapted to their environment;
a good fit
• As descendents 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
• = descent with modification (evolution)
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 successive 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
• Natural selection is the
brain child of 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
• Struggle for existence/Competition
– More offspring are produced than can be supported
by resources
King Penguin Rookery © Momatiuk - Eastcott/Corbis
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
“Survival of the Fittest”
• Organisms are adapted to their environment
through natural selection
• Natural selection is a pessimistic process
1 Population with varied inherited traits
2 Elimination of individuals with certain traits
3 Reproduction of survivors
Certain
individuals with
a distinct,
inherited
characteristic
will be selected
against, while
others with a
(different)
distinct,
inherited trait
will survive
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
• Remember 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 must lead 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
Seed fern: 150 mya
Trilobite: 230 mya
Allosaurus: 65 mya
Evidence for Evolution
• Microevolution – evolution can be observed
in nature (pesticide-resistance in insects,
Peppered moths/industrial melanism)
• A well-known example of microevolution is
the case of the Peppered moths in England
during the Industrial Revolution
• Known as “industrial melanism”
Microevolution
• Prior to the industrial revolution, light variants
of the peppered moth survived better than
dark variants because they blended well with
the light colored trees (caused by the presence
of a light-colored lichen)
• Pre-industrial era – only light variant known
• 1848 – first dark variant collected
• Mid-1900’s – dark variant made up 90% of
population in industrial areas!
Microevolution
• Poor air quality killed the lichens which
covered the otherwise dark trees and
camouflaged the light moths against
predation
• Light moths were predated
on; dark moths were not
• (Prior to the industrial
revolution, the reverse
would be true)
Evidence for Evolution
• Artificial selection – the process by which
humans have modified other species by
selectively breeding for desired traits
• Darwin got the idea of natural selection from
artificial selection!
www.flickr.com/photos/rinalia/
3285371111/
www.flickr.com/photos/
terryandchristine/
2399227035/
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Artificial Selection
• All dogs are domesticated breeds of the Gray
wolf, Canis lupus; “Fido” is actually a
subspecies of the wolf!
Artificial Selection
Evidence for Evolution
• Homologous structures – similar characteristics
that result from a common ancestry
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
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
Evidence for Evolution
Vestigial structures of a whale
http://www.edwardtbabinski.us/mpm/mpm_whale_limb.html
Evidence for Evolution
• In contrast to homologous structures,
analogous structures also provide evidence
for evolution
• Analogous structures are structures that share
similarities by a way of life, not by a common
ancestry
• Analogous structures arise among unrelated
organisms in response to similar needs or
similar environmental factors
Analogous structures
Examples: wings
of insects (a) and
birds (b); flippers
of seals (c) and
penguins (d)
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 welladapted for today may not be so tomorrow…
Evidence for Natural Selection
• Darwin’s fishes of the Galapagos
14 species of finch; 1
common ancestor
(from the mainland);
different beaks
Anatomical Evidence of Evolution
•
•
•
•
Orchid petals - used as pollinator lure
Snake with 2 leg bones (vestigal)
Manatee fingernails (vestigal)
Humans – muscles for wiggling ears
Developmental similarities reflect
descent from a common ancestor
Ontogeny recapitulates phylogeny!
•
•
•
•
Pop quiz time!!!
Which of the bottom images shows a lemur?
A pig?
A human?
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
• Mutation rates in animals and plants average
~1 in every 100,000 genes per generation (a
slow process!)
• Sexual reproduction is a quick and easy (insert
giggling here) means of increasing genetic
diversity and variation, creating geneticallydistinct 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
http://www.bizofshowbiz.com/uploads/Geico%20Cavemen.jpg
Other theories out there
Name
Descent with modification? Common ancestor? Extinction?
Creation (A)
No
No
No
Transformism (B)
Yes
No
No
Evolution (C)
Yes
Yes
Yes
extinction
(A)
change
(B)
change
(C)
change
FSM
• And my personal favorite – The Church
of the Flying Spaghetti Monster!
• Satirical protest to Kansas Board of Education’s
decision to require the teaching of Intelligent
Design, an alternative to Creationism which
avoids specifying identity of ‘designer’
• Founded in 2005
• The FSM is invisible and undetectable;
evidence of evolution planted by FSM
to test “Pastafarian”’s faith
FSM
Evolution
• Remember, evolution is an accepted (and
well-supported) 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
• Distinct from religion, which is neither testable
or falsifiable; nonetheless, debates over
evolution linger on!