Transcript Ch 7 ppt

Evolution
Ch 7
Pt 1
Wooly mammoth skeleton: Mammoths lived 2 million to about
9,000 years ago. They were about 9 to 15 feet tall. Where would
scientists look for possible reasons for extinction?
5 mass extinctions
1 underway
• Evidence of five major mass dying of life
forms on Earth
• Each is followed by a succession of
distinctly different organisms which can
survive in the absence of predecessors
– Example: dinosaurs died
» Gave way to rise of mammals
» Eventually humans appear
Fossil succession shows :
Life, as we can best define it:
• The definition must be “built” on
descriptions that fit all living things.
– Living things are both complex and organized
– Living things grow and reproduce
– Living things respond to stimuli
– Living things acquire and use materials and
energy
– Living things have (use) DNA to store
information
Misconceptions
about
evolution:
??
Evolution proceeds strictly by chance
??
Evolved species must be more complex than the
predecessor
??
Where are the missing links?
??
humans evolved from monkeys so monkeys
should no longer exist
Theory of Evolution
• A theory explains a series of observations and often unifies
related facts through supportive evidence.
• Evolution is based on the observed
accumulated generation to generation
changes within a defined group.
• Evolution accounts for
– similarities among life forms
– differences among life forms
Jean-Baptiste de Lamarck
– (1744-1829) is best remembered for his theory of
Inheritance of Acquired Characteristics:
-- new traits arise in organisms because of their needs
and repetitive behaviors to meet those needs
– Acquired traits are somehow passed on to their
descendants
• Lamarck’s theory seemed logical at the time and
was widely accepted
Lamark’s Theory
Rethinking…
why would giraffes “develop” or actually
“express” the trait of longer necks over time?
Was the “acquired” trait passed on?
Darwin
• In 1859, Charles Robert
Darwin (1809-1882) published
On the Origin of Species
– In it he detailed his ideas
on evolution formulated
20 years earlier
– he proposed a
mechanism for evolution
– From 1831 to 1836, he
had traveled along the
southern continents and
Europe.
What most don’t know about Charles Darwin
• Darwin born in England on Feb. 12, 1809 –
same day as Abraham Lincoln.
• Father a doctor. Mother affluent (Wedgwood
pottery family) .
• Both families were free thinkers and
philosophers.
• His private school education was useless for his
interests; his hobbies hunting, observing natural
world, collecting things, and chemistry.
About the same time…..
– James Hutton was promoting his old earth and
plutonic (igneous) rocks
– and Abraham Werner promoted Neptunism (all rocks
precipitate from oceans).
– Darwin was exposed to Zoomania which promoted
Lamarckian ideas. Learned taxidermy from a former
black slave who inspired Darwin with his stories of the
tropics.
And a little more….
• Off to Cambridge, he studied to be a clergyman.
Baptized into the Church of England, where it was
compatible to be a naturalist.
– He hunted, caroused, and collected beetles.
– he learned to observe variations within a species
from botanist and clergyman Professor Henslow.
– Studied geology with Adam Sedgwick, a
catastrophism proponent who later named the
Cambrian system of rocks in England.
– Learned to do field work and record observations
meticulously.
Darwin spent only 5 weeks in the Galapagos
Islands. Here he made observations about
distinct differences among similar
animals that were directly related to food
supply. He published his ideas in 1859,
24 yrs. later.
Fig. 7-1, p. 115
Observation of finches
in the Galapagos Islands
Insect eaters
Berry
eater
Insect eaters
Seed
eaters
Cactus
eaters
What Darwin noticed
• Plant and animal breeders practice artificial selection
– breeding plants and animals with desirable traits
• A process of selection among variant types in nature
could also bring about change
• Thomas Malthus’s timely essay on population
suggested that human competition for resources and
high infant mortality limited a population size
Natural Selection (Key Points)
The mechanism
• Organisms in all populations posses heritable
variations.
– size, speed, agility, visual acuity, digestive enzymes,
color, and so forth
• Some variations are more favorable than others
– some have a competitive edge in acquiring resources
and/or avoiding predators
• Not all young survive to reproductive maturity
Those with favorable variations are more likely to
survive and pass on their favorable variations
Survival of the Fittest?
• Natural selection is sometimes expressed
as “survival of the fittest”
“Survival of the Fittest”
What does it mean??
• Misconception:
• among animals only the biggest, strongest, and fastest
are likely to survive
– Maybe these traits are an advantage-- but natural selection
may favor species other than the obviously bigger, stronger,
or faster. Examples?
Natural Selection involves differential rates of
survival and reproduction
Survival of the species depends on
producing offspring.
Again, rethinking………
the smallest if resources are
limited
the most easily concealed
those that adapt most readily to
a new food source
those having the ability to
detoxify some substance
Others?
It helps to know what organisms
had survived stressful conditions
in the past ….
The peppered moth
Peppered moths had light colouration,
which effectively camouflaged them
against the light-coloured trees and
lichens which they rested upon
During the Industrial Revolution
in England, many of the lichens
died out, and the trees that
peppered moths rested on
became blackened by soot,
So, is “natural selection” the
mechanism for evolution?
• Natural selection works on existing variations in
a population
– It could not account for the origin of variations
• Critics reasoned that should a variant trait arise,
it would blend with other traits and would be lost
• The answer to these criticisms existed even then
in the work of Gregor Mendel, but remained
obscure until 1900
Gregor Mendel
• controlled genetic experiments with true-breeding strains
of garden peas
– strains that when self-fertilized always display the
same trait, such as flower color
• Traits are controlled by a pair of factors now called
genes
• Genes occur in alternate forms, called alleles
– One allele may be dominant over another
– Offspring receive one allele of each pair from each parent
Mendels Work
• The parental generation
consisted of true-breeding
strains
RR = red flowers
rr = white flowers
• Cross-fertilization yielded a
second generation
all with the Rr combination
of alleles, in which the R
(red) is dominant over r
(white)
Mendel’s Work
• The second generation, when self-fertilized
produced a third generation with a ratio of three
red-flowered plants to one white-flowered plant
Why is this important?
• The factors (genes) controlling traits do not
usually blend during inheritance
• Traits not expressed in each generation may
not be lost even if not seen!
• Some variation in populations results from
alternate expressions of genes (alleles)
– Variation can be maintained!
– **Why is variation important to survival of
a species?
Modern Genetics
Complex, double-stranded helical
molecules of deoxyribonucleic acid
(DNA) called chromosomes are found
in cells of all organisms
Specific segments of DNA are the
basic units of heredity (genes)
The number of chromosomes varies
from one species to another
fruit flies 8; humans 46; horses 64
Modern Thinking
• During the 1930s and 1940s,
– paleontologists, population biologists, geneticists, and
others developed ideas that merged to form a
modern synthesis or neo-Darwinian view of
evolution
• They incorporated chromosome theory of
inheritance into evolutionary thinking
– They saw changes in genes (mutations) as
only one source of variation
Most Importantly
• They completely rejected Lamarck’s idea of
inheritance of acquired characteristics
• They reaffirmed the importance of natural
selection
• But since then, some scientists have challenged
the emphasis in modern synthesis that evolution
is gradual
The Species
• Species
– a population of similar individuals that in
nature interbreed and produce fertile
offspring
– Species are reproductively isolated from one
another
• Goats and sheep do not interbreed in nature, so
they are separate species
• When artifically bred in captivity, offspring are most
often sterile.
Remember…
• Evolution by natural selection works on variation in
populations
– most of which is accounted for by the reshuffling of
alleles from generation to generation during sexual
reproduction
• The potential for variation is enormous with thousands of
genes each with several alleles (varieties), and with
offspring receiving 1/2 of their genes from each parent
• New variations arise by mutations
– change in the chromosomes or genes
Mutations
• Mutations result in a change in hereditary
information
• ONLY mutations that take place in sex cells are
inheritable,
– Can be chromosomal mutations (affecting a large
segment of a chromosome)
– or point mutations (individual changes in particular
genes)
• Mutations are random with respect to “fitness”
– they may be beneficial, neutral, or harmful to survival!
The Species
• Species
– a population of similar individuals that in
nature interbreed and produce fertile
offspring
– Species are reproductively isolated from one
another
• Goats and sheep do not interbreed in nature, so
they are separate species
• When artifically bred in captivity, offspring are most
often sterile.
Recipe for a species
• Speciation is the process by which a new
species arises from an ancestral species
• It involves change in the genetic makeup of a
population,
– which also may bring about changes
– in form and structure
• During allopatric speciation,
– species arise when a small part of a population
becomes isolated from its parent population
Insect
eaters
Berr
y
eater
Seed Cactus
eater eaters
s
Insect
eaters
Variations among “Darwin’s finches” were
naturally selected from among the
existing variations within the gene pool
and mutations that may have occurred.
What would cause the selection of the
observed variations?
Allopatric Speciation
• Reduction of the area occupied by a
species may leave a small isolated
population
– Two peripheral isolates evolved into new
species (i.e. Darwin’s finches)
How long does it take for
changes to appear?
• Although widespread
agreement exists on
allopatric speciation
scientists disagree on how
rapidly a new species might
evolve
• Phyletic gradualism- the
gradual accumulation of
minor changes which
eventually bring about new
species
Punctuated Equilibrium
holds that little or no
change takes place
in a species during
most of its existence
then evolution occurs
rapidly
Styles of Evolution
• Divergent evolution occurs when an ancestral species
giving rise to diverse descendants adapts to various
aspects of the environment
– Divergent evolution leads to descendants that differ
markedly from their ancestors
• Convergent evolution involves the development of
similar characteristics in distantly related organisms
• Parallel evolution involves the development of similar
characteristics in closely related organisms
Divergent Evolution
Convergent Evolution
Parallel Evolution
Evolutionary Novelties
• All land-dwelling vertebrate animals posses
bone and paired limbs so these characteristics
are primitive and of little use in establishing
relationships among land vertebrates
• However, hair and mammary glands are derived
characteristics.
– Only one subclade, the mammals, has them
It wouldn’t be Geology without
Death and Destruction…..
99% of all species that ever
• Perhaps as many as
existed are now extinct
• Organisms do not always evolve toward some kind
of higher order of perfection or greater complexity
• Vertebrates are more complex but not necessarily
superior in some survival sense than bacteria
– after all, bacteria have persisted for at least 3.5 billion
years
• Natural selection yields organisms adapted to a
specific set of circumstances at a particular time
Extinction
• The continual extinction of species is referred to as
background extinction
• It is clearly different from mass extinction during
which accelerated extinction rates sharply reduce
Earth’s biotic diversity
• Extinction is a continual occurrence
– …so is the evolution of new species that usually quickly
exploits the opportunities another species’ extinction
creates
– Mammals began a remarkable diversification when they
began occupying niches the extinction of dinosaurs and
their relatives left vacant
Extinction
• The mass extinction of dinosaurs and other animals at
the end of Mesozoic Era is well known…but not the
greatest loss of biologic diversity!
• The greatest mass extinction occurred at the end
of the Paleozoic Era – end of Permian
– More than 90% of all species died out
– We will discuss these extinctions and their possible
causes throughout the rest of the term
Some predictions from the Theory
of Evolution
Oldest fossil-bearing rocks should have different organisms than
more recent rocks
There should be fossils connecting orders and classes of
descendant organisms.
Closely related species should be similar in anatomy, biochemistry,
genetics
Classification of organisms should show a nested pattern of
similarities
Isolated populations should closely resemble nearer populations
rather than distant ones.
Organisms should show a predicted succession in the fossil record:
fish, reptiles, mammals
Animals that diverged from a common ancestor should evolve to be
more different over time
Homologous or Analagous?
• Homologous structures:
– Similar structure
– Different purpose
• Analagous structures:
– Distinctly different structures
• Similar purpose
Homologous or analagous?
See Page 148 Text.
Forelimb of humans, whales, bats
Wings of birds, bats, flies