Transcript evolution and natural selection - CAPE Biology Unit 1 Haughton

EVOLUTION AND NATURAL
SELECTION
FEBRUARY 18, 2013
CAPE BIOLOGY
MRS. S. HAUGHTON
DEFINITION
• Evolution means change over a period of
time.
• “…evolution can be precisely defined as
any change in the frequency of alleles
within a gene pool from one generation to
the next."
• - Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974
• Individuals don’t evolve, populations do.
• There is no implied “improvement” in
evolution.
• Things don’t change because organisms
want or need them to.
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The study of evolution provides a focus
for investigations into
The nature of life
The origins of life
The diversity of living things
Understanding the similarities in
structure and function they share.
THEORIES
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Theories to explain where life on Earth
came from are varied and uncertain:
Special creation
Spontaneous generation
Steady-state
Cosmozoan
Biochemical evolution
SPECIAL CREATION
• Life was created by a supernatural being
at a particular time.
• Supported by the world’s religions.
• Calculated that creation took place in 4004
B.C.
• A case where faith accepts something for
which there is no empirical evidence.
SPONTANEOUS GENERATION
• Life arose from non-living matter on numerous
occasions.
• Misconceptions: mud/frogs; moldy grain/mice; raw
meat/flies
• van Helmont-dirty shirt / rats (bad science)
• Francesco Redi- meat jars and flies (good)
• Pasteur –soup/germs
STEADY-STATE
• Life has no origin and Earth was always
capable to support life and has changed
very little.
• Theory does not support the evidence of
fossils, however.
COSMOZOAN
• Life arrived on this planet from elsewhere
(outer space).
• Supported by person’s stories of
extraterrestrial and cave drawings of
UFOs.
• Claims made about primitive organisms
being found in meteorites.
• More evidence required.
BIOCHEMICAL EVOLUTION
• Life arose according the chemical and
physical laws.
• Earth very different from it is now (only
simple inorganic substances and high
temperatures).
• Probability of B.E. proven by Stanley
Miller’s experiments.
EARLIEST LIFEFORMS
• Evidence suggests they were heterotrophic.
• Evolved to become photosynthetic, but unstable
and sis not produce energy.
• Later evolved to produce oxygen.
• New oxygen-using lifeforms emerged.
THEORY OF EVOLUTION
• Attempts have always been made to try and
explain the diversity among organisms
• The theory states that evolution is the
development of differentiated organisms
from pre-existing, less differentiated
organisms over a period of time.
• Darwin-On the Origin of Soecies
• Lamarckian – use/disuse theory (giraffe neck
and legs, toe webbing, tails).
EVIDENCE FOR EVOLUTION
Ever wondered about the monkey man thing?
• Palaeontology
• Geographical distribution
• Classification
• Comparative anatomy
• Adaptive radiation
• Comparative embryology
• Comparative biochemistry
Palaeontology
• The study of fossils.
• Supports the theory of progressive
increase in complexity
• Suggests that geographical regions and
climatic conditions changed througout
Earth history
• Fossil types: hard skeletons, petrifaction,
moulds, impressions, imprints, coprolites
Geographical distribution
• Species originate in a particular area
• They disperse out from that area
• Dispersal occurred where land masses were
close together
• Absence of more advanced organisms in a
region indicates prior separation of that region
from the area of origin of those organisms.
• Similar animals in different locations were
the product of different lines of descent
Classification
• Structural similarities between organisms
suggests the existence of an evolutionary
process.
• Result of progressive adaptation.
• Suggest biological organization.
Comparative anatomy
• One of the strongest forms of evidence.
• Organisms with similar anatomical features are
assumed to be relatively closely related.
• Some organisms have anatomical structures
that are very similar in form, but very different in
function. These are called homologous
structures.
• Since these structures are so similar, they
indicate an evolutionary relationship and a
common ancestor of the species that possess
them.
Adaptive radiation
• The evolution of an ancestral species, which was
adapted to a particular way of life, into many diverse
species, each adapted to a different habitat.
• Adaptive radiation has occurred in the evolution of many
groups of organisms.
• E.g. Darwin's finches, 14 species of small land birds of
the Galápagos Islands.
• All the finches derive from a single species of grounddwelling, seed-eating finch.
• Because the environmental niches, or habitats, were
unoccupied on the isolated islands, the ancestral stock
was able to differentiate into diverse species
Comparative embryology
• The embryonic stage for many animals is
very similar.
• For example, fish, bird, rabbit, and human
embryos are similar in appearance in the
early stages.
• They all have gill slits, a two-chambered
heart, and a tail with muscles to move it.
• Later on, as the embryos grow and develop,
they become less and less similar.
Comparative biochemistry
• The occurrence of similar biological
chemicals in different organisms suggests
the existence of biochemical homology
(similarity) among organisms.
NATURAL SELECTION
• The mechanism by which new species
arise from already existing ones.
• Natural selection was proposed by Darwin
and Wallace.
• Takes into account 3 observations and 2
deductions made from the observations.
OBSERVATIONS 1 AND 2
1. Individuals in a population produce more
offspring than necessary.
2. The numbers of organisms in
populations remain constant.
DEDUCTION 1
• Therefore, many individuals fail to survive
or reproduce.
• This is a “struggle for existence” within a
population.
• May be interspecific or intraspecific
competition.
OBSERVATION 3
• Variation exists within all popluations.
DEDUCTION 2
• In the “struggle for existence” the
individuals showing variations best
adapted to their environments have a
“reproductive advantage” and produce
more offspring.
• This is survival of the fittest and leads to
natural selection.
VARIATION AND NATURAL
SELECTION
DEFINITION of VARIATION
• Variation refers to the differences
among individuals of the same species.
• Whereas mitosis leads to identical
offspring as the parent cells, meiosis is
said to lead to variation.
• Except for identical twins, no two organisms
produced by sexual reproduction are alike.
• Therefore, variation or variety exists between
all persons, races and species.
• There are two types of variation:
• Continuous variation and
• Discontinuous variation.
CONTINUOUS VARIATION
• In continuous variation, the characteristic,
trait or quality being studied shows a
gradual difference from individual to
individual.
• There is therefore a range of difference.
• Examples are height and weight.
DISCONTINUOUS VARIATION
• In
discontinuous
variation,
the
characteristic being studied shows
clear-cut differences or boundaries.
• There is therefore no range.
• Examples are blood group or ability to
roll the tongue.
QUIZ
• Are the following examples of continuous or
discontinuous variation?
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Possession of a tail __________
Length of middle finger ____________
Length of hair ___________
Hair colour ____________
Number of legs _____________
Length of hair _____________
Eye colour ______________
Height _____________
Weight _____________
Ability to smell a certain substance ___________
Gender _____________
GENETIC AND
ENVIRONMENTAL
VARIATION
CAUSES OF VARIATION
• The two main causes of variation are:
• GENETIC FACTORS
• ENVIRONMENTAL FACTORS
GENETIC FACTORS
• Due to the genes that are passed on from
generation to generation, there are always
certain gene combinations in different
species and even families.
• Also, the segregation and many different
ways in which chromosomes group up
together (random assortment) during meiosis
to make eggs and sperm will lead to many
differences in variation even within species or
our families; e.g. hair colour, eye colour,
blood groups, height etc.
•
Genetic variation arises by:
1. Meiosis: during segregation of chromosomes in
making eggs and sperm.
2. Fertilization: when eggs and sperm, both
carrying unique genes from mom and dad come
together to make off-spring.
3. Mutation: when a gene changes without
warning.
ENVIRONMENTAL FACTORS
• Characteristic caused by an organism’s
environment are sometimes called
acquired characteristics, because the
variation is due to the limitations
presented by their surroundings.
• E.g. a plant grown in a small pot will limit
its growth to fit in the pot.
• E.g. if water is deep underground, the
normally short roots of plants will grow
very long to reach it.
• Variation leads to natural selection and
evolution over millions of years.
NATURAL AND ARTIFICIAL
SELECTION
DEFINITIONS
•
Selection: the process in which certain
populations are favoured for survival
over others because of useful traits
they may possess.
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Selection pressure: a factor acting on
a population which favours certain
varieties for survival e.g. climate
change
• Natural selection: occurs when the
selection pressure comes from the
natural surroundings or environment of
the populations.
• Artificial selection: occurs when man
determines which population possess
the favourable trait and so encourages
the survival and continuation of that
population.
NATURAL SELECTION IN
NATURE
DARWINIAN THEORY
•
In 1859, a scientist called Charles
Darwin proposed the following theories
to support evolution.
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His theory was called the Theory of
Natural Selection which occurs every
day in nature and is an ongoing process.
1. Variation helps some organisms adapt
better than others
2. Most organisms over-produce their offspring to ensure some survive.
3. Organisms in populations will always be
struggling and competing with other
members.
4. The fittest (best adapted) will survive
5. This ensures that only advantageous
traits are passed on to future offspring.
6. So, over a long period of time, the
population will be left with the stronger
individuals, which are best adapted.
EVIDENCE FOR NATURAL
SELECTION
•
Changes over long periods can be
observed in the fossils of organisms
•
The case of the peppered moth
(polymorphism)
•
Antibiotic resistance in bacteria
POLYMORPHISM
• Polymorphism occurs when two or more clearly
different phenotypes exist in the same population of a
species — in other words, the occurrence of more than
one form or morph.
• In order to be classified as such, morphs must occupy
the same habitat at the same time and belong to
a panmictic population (one with random mating).
• Polymorphism is common in nature; it is related
to biodiversity, genetic variation and adaptation; it usually
functions to retain variety of form in a population living in
a varied environment.Polymorphism results from
evolutionary processes, as does any aspect of a
species.
• It is heritable, and is modified by natural selection.
PEPPERED MOTH
• Natural selection does not always
cause change especially if the
environment remains the same and the
organism is already well adapted.
• In this case, this type of natural
selection is called stabilising selection.
ADVANTAGES AND
DISADVANTAGES OF
NATURAL SELECTION
ADVANTAGES
• The fittest, best adapted organisms
remain in the population.
CARRYING OUT ARTIFICIAL
SELECTION
1. Inbreeding: where Man mates related
organisms to maintain desired traits,
e.g. mating “sibling” dogs to keep size
and fur colour for dog shows.
2. Outbreeding: where Man mates
unrelated organisms from same or
different species to attain desired
traits, e.g. a zebra with a horse to get
a unique striping pattern
ADVANTAGES AND
DISADVANTAGES OF
ARTIFICIAL SELECTION
• Overall advantages are: Man gets the
desired traits that he wants
• Advantage of inbreeding: the desired
trait is maintained throughout the
generations with only slight or
insignificant differences.
• Advantage of outbreeding: outbred
organisms are stronger than inbred
• Overall disadvantage: Loss of diversity; all
individuals are similar
• Disadvantage of inbreeding: unwanted genes
are also passed along through the
generations e.g. diseases
• Disadvantage of outbreeding: the desired
trait is more difficult to attain and maintain
NATURAL SELECTION VS.
ARTIFICIAL SELECTION
• NATURAL
• ARTIFICIAL
• Selection pressure • Selection pressure
from environment
from MAN
• Fittest
individuals • Individuals
with
favoured
desired
traits
favoured
• Change is gradual as • Change is quick to
attain
desired
environment
organism
changes
• Resultant organisms • Resultant organisms
very different
usually different in
small ways
• Offspring
remain • Future offspring may
healthy
develop
complications