Transcript Evolution

EVOLUTION STUDIES
Life Sciences
Hypothesis = a proposed explanation
made on the basis of limited evidence
as a starting point for further
investigation.
Theory = A system of ideas intended
to explain something.
Scientific Theory = Set of principles
that explain and predict phenomena.
Evolution = the gradual development
of something.
Biological Evolution = involves
changes that occur through descent
involving genetic inheritance between
generations.
Theory of Evolution:
Is regarded as a scientific theory
since various hypotheses relating to
evolution have been tested and
verified over time.
Evidence for Evolution:
1)FOSSIL RECORD (Palaeontology):
2) MODIFICATION BY DESCENT
(Homologous structures):
3) BIOGEOGRAPHY:
4) GENETICS:
5) COMPARATIVE EMBRYOLOGY:
Phylogeny
Ontogeny
VARIATION
SPECIES = a group of living organisms
consisting of similar individuals capable of
exchanging genes or interbreeding.
POPULATION = a community of animals,
plants, or humans among whose members
interbreeding occurs, all the inhabitants of
a particular place.
Contributions to variation:
1)Meiosis:
a) Crossing over =
1)Meiosis:
b) Random arrangement of chromosomes =
2) Mutations =
3) Chance fertilisation =
4) Random mating =
Continuous variation = variation that has
no limit on the value that can occur
within a population. A line graph is
used to represent it.
Discontinuous variation = variation in
phenotypic traits in which types are
grouped into discrete categories with
few or no intermediate phenotypes.
Origin of the idea about origins (a
historical development)
Punctuated
equilibrium =
1972
Niles
Eldredge and
Stephen Jay
Gould
Theories of the process of Evolution
1) Lamarckism
(Jean Baptiste de Lamarck –1744–1829)
The idea that an organism can pass on
characteristics that it acquired during
its lifetime to its offspring (also known
as heritability of acquired
characteristics or soft inheritance).
Lamarck’s 1st law:
Law of Use & Disuse
When certain organs became specially
developed as a result of some
environmental need, then the state of
development is hereditary and can be
passed on to the following generation.
Lamarck’s 2nd law :
Law of inheritance of acquired
characteristics:
The inheritance of the newly
developed / lost characteristics by
the following generation, thus the
individual’s inherited the traits of
their ancestors.
Reasons to reject Lamarck’s theory:
1) Characteristics acquired during the
lifetime of a parent are not passed onto the
offspring.
2) An athlete who develops a large muscle
mass through training does not have
children who already possess this large
muscle mass.
3) Ernst Haeckel = In an attempt to disprove
Lamarckism cut off the tails of mice for
several generations. The babies born from
this line of tailless mice still grew tails as
long as their ancestors.
Theories of the process of Evolution
2) Darwinism
(Charles Darwin –1809–1882)
The theory of the evolution of
species by natural selection .
Observations upon which Darwin based
his theory:
1) Organisms of a species produce a
large number of offspring.
2) The offspring naturally show a great
deal of variation.
3) Of the large number of offspring
produced, only a few survive.
4) Characteristics are inherited from
those surviving parents to the
offspring.
Darwin's theory of evolution by natural
selection:
1) Organisms produce a large number of
offspring, that have a great deal of
variation amongst them.
2) Some have favourable characteristics
and some do not.
3) When there is a change in the
environmental conditions or if there is
competition, then organisms with
characteristics which make them more
suited, will survive, whilst organisms
with characteristics that make them less
suited, will die.
4) The organisms that survive, reproduce
and thus pass on the favourable
characteristic to their offspring.
5) The next generation will therefore have
a higher proportion of individuals with
Artificial Selection
The intentional reproduction of
individuals in a population that have
desirable traits.
Artificial Selection - domesticated
animals (selective breeding):
Artificial Selection - domesticated
animals (selective breeding):
Artificial Selection – crop example:
Artificial Selection – crop example:
Similarities between Natural
Selection & Artificial Selection:
1) Want the strongest characteristics
to be passed along generations.
2) Both rely on genotypic and
phenotypic strength.
Differences between Natural Selection &
Artificial Selection:
Natural Selection
1) Driven by nature
2) Variety centred within
natural boundaries
3) Occurs in natural
populations
Artificial Selection
1) Driven by people
2) Variety very different
from nature
3) Occurs only in
domesticated populations
4) Slow process – natural 4) Fast process – driven
time
by people.
Darwin travelled on the HMS Beagle and
studied living organisms in their natural
habitat.
Punctuated Equilibrium
•Darwinism indicates that evolution
takes place through an accumulation
of small or gradual changes that occur
over a long period of time.
•This is supported by the many
transitional fossils in the fossil record
which show the progressive changes
over time.
BUT Punctuated equilibrium explains
the speed at which evolution takes
place, as follows:
1) According to punctuated equilibrium,
evolution is not gradual.
2) Evolution involves long periods of
time where species do not change or
change very little (known as
equilibrium).
3) This alternates with (is punctuated
by) short periods of time where rapid
changes occur through natural
selection.
4) As a result, new species are formed
in a short period of time, relative to the
long periods of no/little change.
5) This is supported by the absence of
transitional fossils (usually termed
missing links) indicating the period of
rapid change.
Formation of new species
Speciation = the formation of new
and distinct species in the course of
evolution. + impact on biodiversity.
Extinction = the state or process of
being or becoming extinct. – impact
on biodiversity.
Speciation through geographic isolation:
1) If a population of a single species
becomes separated by a geographical
barrier (sea, river, mountain, lake), then
the population splits into two populations.
2) There is now no gene flow between
the two populations.
3) Since each population may be exposed
to different environmental conditions,
natural selection occurs independently in
each of the two populations such that the
individuals of the two populations become
very different from each other genotypically
and phenotypically.
4) Even if the two populations were to mix
again, they will not be able to reproduce
with each other. They have thus become
different species.
1) Gene Flow

During migration of individuals from one group to
another, with interbreeding there is a mix of genes
in the gene pool.
ALLOPATRIC SPECIATION –
geographic isolation
Example: Darwin’s finches
Example: Galapagos tortoises
Example: Baobabs & Proteas
SYMPATRIC SPECIATION – due to
natural preferences or influences
Keeping species separate
(Mechanisms of reproductive isolation)
When one species gives rise to two new
species (speciation), the two species
cannot reproduce with each other even if
they mix.
They remain as separate species due to
mechanisms that restrict gene flow
between them.
How each of the reproductive isolation
mechanisms work:
• Breeding at different times of the year
(prezygotic mechanism)
How each of the reproductive isolation
mechanisms work:
• Species-specific courtship behaviour
(animals)
How each of the reproductive isolation
mechanisms work:
• Adaptation to different pollinators (plants)
How each of the reproductive isolation
mechanisms work:
• Infertile offspring (e.g. mules)
Evolution in present times
Natural selection and evolution are still
occurring in present times. Any of the
following examples can illustrate that:
1) The use of DDT and the consequent
resistance to DDT in insects which can
be explained in terms of natural selection
2) The development of resistant strains
of tuberculosis-causing bacteria (MDR
and XDR) to antibiotics due to
mutations (variations) in bacteria and
failure to complete antibiotic courses
3) HIV resistance to anti-retroviral
medication