Download Darwin`s Influences

Evolution
Evolution and the Theory of
Natural Selection
Developing a Theory of Evolution
• Evolution is undeniable. Evolutionary
theory is a collection of carefully reasoned
and tested hypotheses about how
evolutionary change occurs.
• Today’s physicists don’t completely
understand gravity, but it exists.
Influences on Darwin’s
Ideas
Jean Baptiste de Lamarck
• (1744-1829) –
one of the first
to recognize
that living
things changed
over time.
3 assumptions:
• Organisms had an inborn urge to better
themselves
• Change occurred because organisms could
alter their shape based on their needs.
• by trying to fly, birds grew wings.
• Organisms could pass on acquired traits from
generation to generation
• Remember: Lamarck did not understand
genetics
Theory of “Use vs. Disuse”
• The long necks of
giraffes were due to their
stretching for food, and
giraffes passed their
stretched necks on to
their offspring.
• Similarly, the big,
“ripped” muscles
developed by the
village blacksmith with
all his hammering and
slinging of heavy metal
objects would be
expected to be passed
on to his offspring.
Charles Lyell
• Lyell demonstrated
the earth was very
old (4.6 billion years)
Charles Lyell
• Without that information, Darwin’s theory
could not work – it would have taken long
periods of time to evolve millions of
species.
• Darwin witnessed changes in earth
geography – volcanoes, earthquakes – if
the earth can change, so, too could life on
the earth
Farmer’s influence:
• Darwin spoke to plant and animal
breeders
• Breeders altered and improved crops and
livestock
• Darwin wanted to know how these
breeding programs work?
Farmer’s influence:
• Farmers could not cause variation to occur, it
happened or it did not.
• If variation occurred, the farmers could take
advantage of it.
• Breeding cows that gave most milk, or other
desirable characteristics – artificial selection
• Darwin believed that nature must have a similar
process – only allowing the organisms best
suited to their environment to survive – Natural
Selection
Malthus: Population Controls
• Thomas Malthus was an Economist
• observed that babies were being born at a
faster rate than people were dying
• Sooner or later, not enough food or
resources
Malthus: Population Controls
• Darwin realized that this applied to
animals even more than people. Most
animals made more offspring
• Most baby organisms die, and very few
survive to raise their own offspring
• What allows them to survive and raise
offspring? Fitness
Darwin made some profound
observations, from which he inferred
some brilliant conclusions...
• Observation #1. All species have huge potential
fertility
• Observation #2. Except for seasonal fluctuations,
populations tend to maintain a stable size.
• Observation #3. Environmental resources are
limited.
Natural Selection
The Four Basic Ideas
Natural Selection
1. Organisms are capable of producing huge
numbers of offspring.
2. Those offspring are variable in appearance and
function, and some of those variations are
heritable.
3. Environmental resources are limited, and
those varied offspring must compete for their
share.
4. Survival and reproduction of the varied
offspring is not random. Those individuals
whose inherited characteristics make them
better able to compete for resources will live
longer and leave more offspring than those not
as able to compete for those limited
resources.
Genetics and Evolutionary Theory
• Peppered moths
• Verified by HBD
Kettlewell
experiment
• Darwin did not
have the benefit
of understanding
of genetics
Genetic Variation
• Genes are the sources of random variation
• Genetic variation does not occur because
an organism wants it to (as Lamarck
suggests)
• All members of a population (group of
individuals of the same species) share a
common group of genes – the gene pool.
Species
• Species is a group of similar-looking
(though not identical) organisms that
breed with one another and produce fertile
offspring in the natural environment.
• Speciation
• Speciation is a process of organisms
evolving into new species
Niche
• A combination of where an organisms lives
and what functions it performs are called
its niche
• No 2 species can occupy the same niche
in the same location for a long period of
time.
Reproductive Isolation
• Scientists have learned that new species
usually form only when populations are
isolated, or separated
• Species that are separated so they do not
interbreed is called reproductive
isolation
• Gene pools become dissimilar
Allopatric Speciation
• A population becomes physically separated
from the rest of the species by a
geographical barrier that prevents
interbreeding.
• Because gene flow is disrupted by this
physical barrier, new species will form.
Sympatric Speciation
• Two populations are geographically
close to each other, but they are
reproductively isolated from each
other by different habitats, mating
seasons, etc.
Finches of Galapagos
• Darwin observed finches on the
Galapagos Islands
• 14 different finches – evolved from a
common ancestor
• All have body structures and behaviors
that allow them to live in different niches
Finch Feeding Styles
•
•
•
•
Some feed on small seeds
Some crack open larger seeds
Some pick ticks from reptiles
Some use twigs to get insects out of dead
wood
• Vampire finches – drink blood of seabirds
What may have happened?
1. Founding fathers and mothers – ancestral
finches found the Galopagos Islands
(finches do not like to fly over water for any
distance) – They may have gotten lost, or
blown off course etc.
2. Separation of populations – Some birds from
one island (A) crossed to another island
(B).
3. Changes in the Gene Pool - Over time, each
population adapted to the needs of their
environment
What may have happened?
4. Reproductive isolation – Birds from A cross
to B. Will they be able to breed with birds
from B? Probably not. Beak size, shape
whatever.
5. Sharing the island – 3 possibilities –
–
–
–
Coexistence – would need different niches
Extinction – competition with one better suited
than the other for that niche
Further Evolution - if one exhibits enough
genetic variation, competition will cause further
evolution.
Adaptive Radiation
• The process of one species giving rise
to many species is called adaptive
radiation or divergent evolution
Convergent evolution
• A phenomenon in which adaptive
radiation among different organisms
causes different species that have
similar appearance and behavior –
example – fish pectoral fins, dolphin
fins
Analogous structures
• structures with similar function and
appearance but from different
organisms
Genetic Drift
• We now know that gene pools can change,
even without natural selection – this is
Genetic Drift.
• If an individual produces more offspring than
others of the species – by chance
• Usually occurs in small populations *
• Environmental events can wipe out many
individuals that do not carry a particular
allele – that allele becomes more prevalent
All characteristics do not have to
contribute to “Fitness”
• Rhinoceros’ – African – two horns,
Indian – 1 horn
• Horns are an advantage, but number of
horns doesn’t make a large difference
Stabilizing Selection
• All species do not change all of the
time
• Stabilizing Selection – when organisms
are well suited to their environment and
natural selection does not favor
changes – example: shark, Limulus,
turtles, ferns
Pace of Evolution
• some scientists say speciation is the eventual
outcome of gradually accumulating changes of
ancestral species – this is called Gradualism (trouble
is – fossil records are incomplete)
• Mass Extinction - the result of dramatic change in
environment that results in many species vanishing
• Recently findings indicate that a species lived for
long periods then “suddenly” (million years) a new
set of different, but related organisms took their
place for a long time – Punctuated equilibrium
Hardy-Weinberg
•
HW law states --> original of a genotypes alleles remains CONSTANT
•
HW Equilibrium... is defined algebraically
any gene with 2 allelic forms...
A and a
• let frequency of one allele (A) = p & frequency of other allele
(a) = q
•
•
•
then by definition,
HW equation...
p+q = 1
(p + q)2 = p2 + 2 pq + q2 = 1
GG
Gg
gg
Hardy-Weinberg
• What are the H-W frequencies for the
following population of plants with different
colored flowers?
• 63 red (RR), 294 pink (Rr) and 343 white (rr)
= 700 plants, 1400 genes or alleles
• Is the population in H-W equilibrium?
Anthropological Evolution
• The history of hominids
(Present day & extinct)
Phylogeny
• The history of hominid life depicted as a
branching tree
• Earliest hominids are placed at the trunk
• Each branch represents a new species which
inherits many traits from the ancestor but
also has a new trait which appear for the
1st time
Phylogenetic Tree