Transcript evolution by natural selection - Cal State LA

Biol 350: Evolution
Course website:
instructional1.calstatela.edu/pkrug
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click on “Bio 350” to get powerpoint files, study guides, syllabus
Pre-requisite: Genetics (Biol 340)
you will be dropped without notice if you don’t
have this pre-req
Biol 350: Evolution
In 1987, Supreme Court ruled that states cannot require public
schools to balance evolution lessons by teaching creationism
Oct 2004 – school board of Dover, PA implements 1st required
lesson on Intelligent Design in U.S. public schools
Nov 2005 – 8 school board members voted out of office
Dec 2005 – school board’s policy overturned by federal judge
Jun 2008 – Louisiana Gov. Jindal signs “Louisiana Science
Education Act” to allow teaching of Intelligent Design
Politics of Knowledge
Evolution in the 1800’s
A story of thinkers, adventurers, and
the peculiar things they found on islands
Lamarck - “Acquired Characters”
1809 - French biologist proposed that species had changed
over time, and were related by common ancestry
Proposed that individuals changed
to meet the needs of their
environment, and that these
acquired characters were
then passed on to their offspring
Most famous idea - giraffes stretched
their necks to reach high tree branches,
so their offspring inherited longer necks
The Birth of Evolutionary Theory
In the early 1800’s, some enterprising young men began
exploring the world’s biodiversity with an eye for pattern
and process in the natural world.
One was Charles Darwin
- educated, from a wealthy family
- destined to become a preacher,
he set off to explore the world after
college (1832-1836)
- collected and observed animal
life from islands on the Beagle
Evolution and Islands
Islands present simplified examples of ecology & evolution
- fewer species
- extreme modifications of what you find on the mainland
(it’s just obvious that things have changed)
- distinct but related forms from nearby islands, mainland
Darwin’s journeys allowed him to visit the Galapagos islands
off South America, where he found...
- giant tortoises (900 lb, 6 feet long, live for 170 years!)
- algae-eating iguana lizards
- distinct species of finches &
mockingbirds on different islands
Evolution and Islands
Darwin observed that neighboring islands in the Galapagos
had similar, but different, species of mockingbirds
Descendents of one lost
bird from the mainland
colonized the islands..
..over time, became
4 different species
on different islands
Evolution and Islands
Darwin set off on the Beagle with no clear notion
of evolutionary patterns
- returned with basic ideas of his theory + supporting data
However, he knew that proposing how species “came into
existence” would create controversy in Victorian England
- sat on his theory for 20 years, writing Origin of Species
Evolution and Islands
In 1854, a scientific paper contained this important quote:
“Every species has come into existence coincident
both in space and time with a pre-existing, closely
allied species.”
- first suggestion that new species appear not just near,
but actually from, other species
Evolution and Islands
In 1854, a scientific paper contained this important quote:
“Every species has come into existence coincident
both in space and time with a pre-existing, closely
allied species.”
- first suggestion that new species appear not just near,
but actually from, other species
….but this insight didn’t come from Darwin.
It came from a young guy named Alfred Russell Wallace,
another adventurous explorer
Alfred Russell Wallace
Wallace’s family lost their fortune, so he worked, educated
himself, and took off to explore the world as a young man
While Darwin sat home writing his book, Wallace travelled the
world, financing his epeditions by collecting and selling
animals
Wallace’s collections gave him
insight into:
- variation within a species
(all individuals are not the same)
- geographical distribution of species
(not random)
Alfred Russell Wallace
His observations suggested that geographical boundaries
could explain species distributions
one species
of spider
monkey
P. irrorata
Alfred Russell Wallace
His observations suggested that geographical boundaries
could explain species distributions
Different
species
of spider
monkey
P. monachus
one species
of spider
monkey
P. irrorata
Alfred Russell Wallace
His observations suggested that geographical boundaries
could explain species distributions
3rd species, as
predicted by
Wallace,
P. pithecia
Different
species
of spider
monkey
P. monachus
one species
of spider
monkey
P. irrorata
- rivers delineated boundaries between related species
3) Indicated that seemingly related forms of life tended
to exist on neighboring islands…
…UNTIL he crossed from Bali to Lombok
A Malay Mystery
As he moved from Sumatra to Java to Bali, Wallace
found similar bird species…
but then:
“On crossing to Lombok, separated from Bali by a
strait less than 20 miles wide, I naturally expected to
meet with some of these birds again; but during a stay
there of 3 months I never saw one of them, but met
with a totally different set of species, most of which
were utterly unknown not only in Java, but also in
Borneo, Sumatra and Malacca.”
A Malay Mystery
- came to be known as Wallace’s Line, dividing:
Borneo from Celebes, and Bali from Lombok
A Malay Mystery
- came to be known as Wallace’s Line, dividing:
Borneo from Celebes, and Bali from Lombok
Bali + points west
Lombok + points east
Tigers
Cockatoos
Bears
Birds of Paradise
Orangutans
Cuscuses & other marsupials
Monkeys
Tree kangaroos (filling niche of
missing monkeys)
Beginnings of Biogeography
Why such a difference? Geological history of the islands:
- Bali lies on the continent shelf; was once part of mainland
along with Java, Borneo and Sumatra
- Lombok and islands to the east are in deep water off the
continental shelf; were never attached to mainland Asia
- are on the same tectonic plate as Australia & New Guinea,
and share their assemblage of animals
Today, biogeography is the study of geographical patterns
in the distribution of species, and the causes behind them
Darwin vs. Wallace
Wallace had started off his travels with the question
already in mind: What is the origin of species?
- most people viewed the arbitrary and inscrutable
arrangement of living things as divine whimsy
Wallace had “always been interested in the geographical
distribution of animals and plants”
- felt that the information in natural history observations
and recorded distributions “..had never been properly
utilized as indications of the way in which species came
into existence.”
Darwin vs. Wallace
Wallace pointed out that old islands have more endemic
(unique) forms of life than young islands
- isolation + time = new species; think about why
- for example, Madagascar: 60 million years old:
80% of plants are endemic, 90% of reptiles, all primates
Wallace also pointed out the Galapagos, as volcanic islands,
had never been attached to the mainland
“they must have been first peopled by the action of winds
and currents… the original species die out, and the
modified prototypes remain.”
Endemic species
Madagascar
Aepyornis maximus (giant ostrich)
dwarf chameleon
pygmy hippo
Malaysia
Pygmy rhino
Catalina Island
Rattle-less rattlesnake
New Zealand
Tuatara, Kiwi
Komodo
Komodo Dragon
Mauritius
Dodo
Darwin vs. Wallace
Wallace had the theory to contest Special Creation
(evolution), but not the mechanism (natural selection)
He and Darwin then began corresponding
- both heavily inspired by Malthus, who wrote about
exponential population growth
In 1858, Darwin received a manuscript from Wallace
outlining the basics of evolution via natural selection
- his friends urged him to quickly write up a summary of
his 20 years’ worth of thoughts + data
- both papers were read aloud together and published
Darwin vs. Wallace
The following year (1859), Darwin published his book
On the Origin of Species by Means of Natural Selection,
or the Preservation of Favoured Races in the Struggle for Life
History subsequently largely forgot about Wallace...
.. but his independent derivation of the role of natural
selection was important in convincing other scientists of
the plausibility of this revolutionary new theory
Evolution by Natural Selection
Darwin’s theory had 4 postulates, or underlying assumptions:
(1) Individuals within a species are variable
(2) Some of this variation is passed to offspring
(in other words, traits are heritable)
(3) In every generation, more offspring are produced than
can survive (due to limited resources)
(4) Survival and reproduction are not random:
- individuals with the most favorable variations survive,
or produce the most young
- this is the principle mechanism of evolution, called
natural selection
Evolution by Natural Selection
Darwin’s 1st postulate:
(1) Individuals within a species are variable
Evolution by Natural Selection
Darwin’s 1st postulate:
(1) Individuals within a species are variable
Mean beak depth
Evolution by Natural Selection
Darwin’s 2nd postulate:
(2) Some of this variation is passed to offspring
(in other words, traits are heritable)
Evolution by Natural Selection
Darwin’s 3rd postulate:
(3) Every generation, more offspring are produced than
can survive (inspired by Malthus)
Organism
aphid
Reproductive potential
524 billion in one year
elephant
19 million in 750 years
a bacterium
cells cover earth 7 feet deep in 2 days
Starfish
1079 offspring in 16 years
Evolution by Natural Selection
Darwin’s 4th postulate:
(4) Survival and reproduction are not random:
- individuals with the most favorable variations survive,
or produce the most young
- this is the principle mechanism of evolution, called
natural selection
Evolution by Natural Selection
Darwin’s 4th postulate:
natural selection
Before drought
Beak
depth
Evolution by Natural Selection
Darwin’s 4th postulate:
natural selection
- drought selected against
shallow beaks
- only deeper beaks could
crack the tough seeds
that were now available
After drought
Beak
depth
Evolution by Natural Selection
A change in the genetic makeup of a population is termed
evolution
- this can happen by chance, by natural selection, by human
breeding programs, etc.
Natural selection causes evolution that results in adaptation,
producing organisms that are better suited to their particular
environment
- adaptation increases fitness, the ability of an organism to
survive and reproduce (contribute to next generation)
Acquired traits?..
Natural selection was the process unrecognized by his
predecessors such as Lamarck, who preached that
acquired traits could be passed to offspring
(i.e, giraffes who kept trying to reach the higher branches)
For instance, who wouldja think wrote this:
“I think there can be little doubt that use in our domestic animals
strengthens and enlarges certain parts, and disuse
diminishes them; and that such modifications are inherited.”
Acquired traits?..
Natural selection was the process unrecognized by his
predecessors such as Lamarck, who preached that
acquired traits could be passed to offspring
(i.e, giraffes who kept trying to reach the higher branches)
For instance, who wouldja think wrote this:
“I think there can be little doubt that use in our domestic animals
strengthens and enlarges certain parts, and disuse
diminishes them; and that such modifications are inherited.”
 from Darwin’s Origin of Species!
Darwin & acquired traits
-and“The wingless condition of so many [island] beetles is
mainly due to the action of natural selection, but
probably combined with disuse”
“For during thousands of successive generations each
individual beetle which flew least, either from its wings
having been ever so little less perfectly developed
or from indolent habit, will have had the best chance
of surviving from not being blown out to sea”
- Origin of Species
Darwin & acquired traits
-and“The wingless condition of so many [island] beetles is
mainly due to the action of natural selection, but
probably combined with disuse”
“For during thousands of successive generations each
individual beetle which flew least, either from its wings
having been ever so little less perfectly developed - yeah!
or from indolent habit, will have had the best chance
of surviving from not being blown out to sea”
- Origin of Species
Darwin & acquired traits
-and“The wingless condition of so many [island] beetles is
mainly due to the action of natural selection, but
probably combined with disuse”
“For during thousands of successive generations each
individual beetle which flew least, either from its wings
having been ever so little less perfectly developed
or from indolent habit, will have had the best chance
of surviving from not being blown out to sea”
Mm, not so much
- Origin of Species
Problems with Darwin’s Explanation
There were two major problems in Darwin’s theory:
(1) Darwin didn’t have any knowledge of Mendelian
genetics, so he didn’t get how heritability worked
(2) mutation had not been discovered, so Darwin couldn’t
explain where variation came from
(especially new variations)
The Modern Synthesis
This was solved between 1932-1953 in a series of books
that integrated genetics with evolution by natural selection
- this is termed the Modern Synthesis
- explained things in terms of alleles, which are different
versions of a given gene
The Modern Synthesis
Modern synthesis restated Darwin’s 4 postulates:
(1) Individuals in a population are variable for most traits,
because mutation creates new alleles and sexual
reproduction creates new allele combinations in every
generation
(2) Individuals pass their particular alleles to their offspring
(3) More offspring are produced than can survive
(4) Individuals that survive, or reproduce the most, have
allele combinations that best adapt them to their
environment
Darwin’s Particular Genius
Over his career, Darwin wrote about 3 kinds of selection:
(1) Natural selection
- makes a species better adapted to its environment
- increases survival
(2) Sexual selection
- makes one sex more appealing to the other
- increases reproduction
(3) Artificial selection
- we choose desired traits and amplify them through
selective breeding of domestic organisms
In the 150 years since, no one has come up with another kind
Variation comes first
The central principle of Darwinian evolution by natural selection
is variation precedes adaptation
- mutations come first and happen by chance
- if a mutation confers an advantage, its frequency tends to rise
- this causes a population to evolve because its allele
frequencies change over time (one allele gets more common)
- also means the population becomes better adapted to
its environment (more individuals have the good allele,
which increases survival)
Individuals cannot “try to mutate” to survive
Some things to Remember
1) evolution is defined as genetic change in a population
over time – a change in allele frequencies
- not all evolution is driven by selection, thus not all evolution
produces adaptation
- random or chance deaths can change the genetic makeup of
a population, but won’t necessarily make that population
better adapted to its environment
- such non-adaptive, random change is called
genetic drift; we will talk about this a lot more, later on
Some things to Remember
1) evolution is defined as genetic change in a population
over time – a change in allele frequencies
- not all evolution is driven by selection, thus not all evolution
produces adaptation
2) natural selection works on individuals, but evolution
happens to populations
3) selection acts on phenotypes (what you see), not
directly on the alleles that cause those phenotypes
4) selection can’t act on anything that’s not genetically
based – acquired traits may cause you to live or die, but if
they aren’t passed on to offspring, evolution doesn’t result
Some important books about islands:
Origin of Species
(Charles Darwin, 1859)
Island Life
(Alfred Wallace, 1880)
Theory of Island Biogeography
(Robert MacArthur and Ed Wilson, 1967)
Song of the Dodo
(David Quammen, 1996)