Topic 10: How do living things evolve

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Topic 10 How do living things evolve?
Darwin and Beyond
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Charles Darwin - (1809 1882)
Enter Charles Darwin
Physician -Theologian - Naturalist

• Prevailing view one of Gods static perfect
  world

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Darwin on the HMS Beagle
Joined as the Naturalist

• Primary commission of the Beagle was to map the
  coastlines and harbors of South America

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Route of the Beagle
www.oum.ox.ac.uk/learning/htmls/images/map.gif
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Major impacts on Darwins thinking as he sailed
on the HMS Beagle
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Observes shell exposed bed on land (some shells
same as modern species)
must have been underwater at one time, then
uplifted
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January 16, 1832, the H.M.S. Beagle, made its
first stop at São Tiago in the Cape Verde islands
off the west coast of Africa.
Years later, Charles Darwin wrote
"The geology of St. Iago is very striking yet
simple a stream of lava formerly flowed over the
bed of the sea, formed of triturated recent
shells and corals, which it baked into a hard
white rock.
Since then the whole island has been upheaved.
But the line of white rock revealed to me a new
and important fact, namely that there had been
afterwards subsidence round the craters, which
had since been in action, and had poured forth
lava.
It then first dawned on me that I might write a
book on the geology of the countries visited, and
this made me thrill with delight. That was a
memorable hour to me. . . . (Autobiography, p.
81).
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Darwin experiences an earthquake in Chile
. . . I happened to be on shore . . . Lying in
the woods to rest myself. It came on suddenly
and lasted two minutes, but the time appeared
much longer.

• The motion made me almost giddy it was something
  like . . . That felt by a person skating over
  thin ice, which bends under the weight of the
  body.

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Fossils of extinct animals
Fossils outnumber living forms?

• Driven to extinction?

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Biological - Diversity of Plants animals
Huge diversity of plants and animals
Differ from continent to continent
Rhea (4), Emu (6), Ostrich (8)

• Separation caused differences

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Galapagos Islands
Island organisms (endemic) were similar to
mainland organisms
Examples Tortoises Finches
http//www.ecuador.us/images/mapgalap.gif
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Saddle-backed tortoises are found on low, arid
islands
Dome-shaped tortoises are found on high, humid
islands
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Darwins Finches
Different species with different shaped beaks

• All descendents of mainland ground finch

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Years After The Beagle
Idea of Evolution not immediately apparent
Worked on other studies including his discussion
of geological observations and a lengthy work on
barnacles
http//shots.oxo.li/hot/OXO-World/Charles_Darwin.j
pg
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Rev. Thomas Malthus(1766 1834)

• Essay on the Principle of Population
• Without external controls, the human population
  would outstrip its ability to feed itself

www.nndb.com/people/250/000024178/malthus.jpg
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Malthusian Crisis
population
resources
Population Increase exponential
growth Resources (e.g., food) arithmetic growth
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A letter from Alfred Wallace (1823-1919)
In June 1858 Wallace sent Darwinhis essay, On
the Tendency of Varieties to Depart Indefinitely
From the Original Type
Charles Lyell and Joseph Hooke decided to present
the essay with excerpts from a paper that
Darwin had written in 1844 but kept confidential,
to the Linnaean Society of London on 1 July 1858,
highlighting Darwin's priority.
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On the Origin of Species
Published on 24 November 1859

• 20 years after voyage

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Summary of Darwins Ideas

• Reproductive Potential to overpopulate the Earth
  populations relatively stable (struggle for
  existence)

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Summary of Darwins Ideas

• Large percentage of members of a population must
  die early (who lives / who dies if all
  individuals are identical?)

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Summary of Darwins Ideas

• Variation exists among individuals of a
  population leads to increased chance of
  survival of some relative to others in the
  population

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Darwin a pigeon breeder
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• Inferred environment could play role of breeder

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Summary of Darwins Ideas

• Those with traits most adapted to the environment
  more likely to survive to reproduce and produce
  more offspring than those that are less well
  adapted (survive to reproduce)

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Natural Selection leads to Differential
Reproduction

• Results in population changing (Evolving) over
  time
• Environment not constant so best adapted
  organisms continually change
• Natural Selection non-teleological
• Enough time ? formation of new species and
  diversity of life on Earth

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Evidence of Evolution(revisited)
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Biogeography (geographic distribution of species)

• Convergent evolution - marsupials
  - placental animals
• Living things are what and where they are today
  because of events in the past

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Fossil Record

• Sequence was consistent with history of
  vertebrate descent (it collaborated with other
  evidence)

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Comparative Anatomy

• Common descent evident in anatomical similarities
  between species
• Evolution as a remodeler ? ancestral structure
  function one way modified to take on new function
• Structures with same evolutionary and embryonic
  origin in different species called homologous
  structures

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Homologous Structures

• Same skeletal elements make up forearm of human,
  lizard, cat, whale, bat, frog, bird

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Comparative EmbryologySimilar embryonic
development
human
chicken
dog
tortoise
chicken
human
dog
tortoise
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Molecular Biology

• Similarity in DNA and proteins shows degree of
  relatedness among species

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Molecular Biology

• Remember this is NOT LINEAR but BRANCHING

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Natural Selection in the Wild
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English Peppered Moth

• 2 morphs light and dark
• Eaten by visual predator (birds)
• Change in environment yields change in morph

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Natural Selection vs. Evolution

• Isnt about individual moths changes occur in
  population
• NATURAL SELECTION acts on the individual
• EVOLUTION acts on the population

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Remember Natural Selection
Targets the individual phenotype (characteristics)
usually results in an decrease in genetic
variability
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Has nothing to do with
how strong it is
its ability to withstand environmental extremes
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But does deal with
how many fertile offspring it has
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Evolution

• Targets the population's gene pool (alleles)
• Therefore is a change in gene frequency

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Forms of Selection
http//www.sparknotes.com/biology/evolution/natura
lselection/section1.html
Directional Selection
Disruptive Selection
Stabilizing Selection
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• Darwin did not know the mechanism of inheritance
  (genetic basis)

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Misconceptions to think about

• Evolution has never been observed
• Evolution violates the 2nd law of thermodynamics
• There are no transitional fossils
• Evolution proceeds by random chance
• Evolution is only a theory

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From The Origin of Species

• There is grandeur in this view of life, with its
  several powers, having been originally breathed
  into a few forms or into one and that, whilst
  this planet has gone cycling on according to the
  fixed law of gravity, from so simple a beginning
  endless forms most beautiful and most wonderful
  have been, and are being evolved.

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