biol 350: evolution

Biol 350: EvolutionCourse website:

instructional1.calstatela.edu/pkrug

NO WWW at beginning!

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: EvolutionIn 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 TheoryIn 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 IslandsIslands 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 IslandsDarwin 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


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


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)


His observations suggested that geographical boundaries could explain species distributions

one speciesof spidermonkeyP. irrorata



Different speciesof spidermonkeyP. monachus




3rd species, as predicted byWallace,P. pithecia

- rivers delineated boundaries between related species

Different speciesof spidermonkeyP. monachus


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 BiogeographyWhy 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.”

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.”

Darwin vs. Wallace

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 SelectionDarwin’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:



Darwin’s 1st postulate:


Mean beak depth


Darwin’s 2nd postulate:

(2) Some of this variation is passed to offspring (in other words, traits are heritable)


Darwin’s 3rd postulate:

(3) Every generation, more offspring are produced than can survive (inspired by Malthus)

Organism Reproductive potentialaphid 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


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


Darwin’s 4th postulate: natural selection

Before drought

Beakdepth


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

Beakdepth


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


-and-



- Origin of Species

- yeah!


-and-



- Origin of SpeciesMm, not so much

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 SynthesisModern 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 GeniusOver 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 firstThe 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 Remember1) 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 Remember1) 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)

biol 350: evolution

Documents

different species

new species

galapagos islands

different islandsevolution

nearby islands

neighboring islands

beagle evolution

existence coincident