Transcript Evolution and Natural Selection

EVOLUTION
Definition
• Change in the structure, function and
behaviour of organisms between generations
over time.
• It has only been in the last 200 years that the idea
that species might change has come about
• Fossils of organisms that once existed soon became
discovered which made scientists wonder why some
species disappear= some of the first evidence for the
theory of evolution
Do species change over time?
Have we evolved from a common ancestor?
• There are 9 million different species on Earth- 1.2
have been described, classified and named
What accounts for this biodiversity?
History of the theory of evolution
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Carl Linnaeus
James Hutton
Georges Cuvier
Thomas Malthus
Jean B. Lamarck
Charles Lyell
Charles Darwin
Alfred Wallace
Gregor Mendel
Alfred Wegener
• Questions on website
• Alfred Russell Wallace in the Malay Archipelago from
1854-1862 began to wonder about how species
evolved from the distribution of species. He wrote a
paper and his ideas were similar to Darwin who had
been reluctant to publish his findings of the last 20
years.
• In 1859 Darwin wrote his book ‘ The origin of species
by means of natural selection’. It became one of the
most influential books of all time.
• It outlined his theory of evolution by natural
selection.
Darwin’s four main observations
• Offspring generally appear
similar to their parents.
• No two individuals are
identical
• Organisms have the ability to
produce large numbers of
offspring
• Populations in nature tend
to remain fairly stable in size.
Natural Selection
• Process by which organisms most suited to
their environment are most likely to survive
and pass their genes on to their offspring
( those less well adapted produce fewer
offspring or do not breed at all)
Survival of the fittest
• Variation in organisms characteristics are caused
by the organisms having different DNA (genes).
These genes are produced as a result of
mutations and / or during meiosis.
• Some differences enable the organism to survive
better (compete more successfully)
• The ones with beneficial DNA survive, breed and
pass on their DNA to the next generation
= SURVIVAL OF THE FITTEST
• Those without beneficial DNA die before they
reproduce, so their DNA is less likely to be passed
on.
• The beneficial DNA increases in frequency in the
population and over time may eventually
produce a new species.
New species
• For new species to arise there needs to be:
-variation
-isolation and competition
-selection and speciation
• In meiosis several factors assist to mix up the
maternal and paternal DNA within the cell:
-interphase: mutations can occur when DNA is
replicating
-prophase I: crossing over of homologous
chromosomes to produce 4 unique chromatids
-anaphase I: separation of homologous chromosomes
occurs randomly
Results in 4 haploid gametes each with a unique set of
DNA which produce further variation through sexual
reproduction and fertilisation
Isolation and competition
• Because individuals over produce, yet populations
remain stable COMPETITION must take place.
• Ie. Thomas Malthus- a much larger number of
individuals are produced than can possible survive
• In COMPETITION there are “winners” and “losers”.
Winners are better adapted with more useful
characteristics, they are more able to survive and
breed, so pass on their beneficial DNA.
• Over time when this happens continually, accumulated
changes can give rise to a new species- speciation
• Two populations of the same species may
become isolated from one another due to
continental drift, earthquake etc.
• This could lead to speciation
Selection and speciation
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Competition for food, water
Predation
SELECTION PRESSURES
Disease
Physical and chemical factors
Competition for mates
Competition for space, nesting sites, territory etc
A section of DNA that helps an organism compete
better is “selected for”, so it increases in frequency
• A section of DNA that fails to help an organism survive
is usually “selected against”, so it decreases in
frequency
A few South American finches
arrived to the islands (with slight
genetic variations. Eg colour
Drier islands had seeds with thick
coats
Natural selection would have
favoured birds with larger,
stronger beaks
They were better able to survive,
breed and pass on the genes of
larger, stronger beaks
Over time the whole population
had larger stronger beaks
When no longer able to breed
with those with shorter beaks
they are different species
They are different
species but are
closely related
• Darwin proposed that Natural Selection could
lead to new species being produced over time.
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This was his explanation for the large
number of different species of finch found in
the Galapagos Islands.
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Each species has adaptations to its body,
beak and feet that allow it to feed on specific
types of food in specific areas.
What is a species?
• Definition
Evolution of a new species
• Speciation occurs when there is a
“Reproductive Barrier”, some thing that stops
members of an original population passing
their DNA freely among all members, ie
PREVENTS FREE GENE FLOW
• The barrier may be a geographical barrier =
ALLOPATRIC speciation
• The barrier may be behavioural, biochemical,
or anatomical =SYMPATRIC speciation
Allopatric speciation
Sympatric speciation
• When there is NO geographical barrier
• Initially individuals in the original species may
have variations that can be divisive of the
population.
• Eg in birds some might have slightly:
-different shaped beaks
-shorter wings,
-better nocturnal vision,
-different colour plumage or courting behaviour, etc
• https://www.youtube.com/watch?v=Q2vsG77
PZ80&feature=youtu.be
Peppered moth simulation
Go to:
http://biologycorner.com/worksheets/pepperedmoth.html
• Read through the information and follow the instructions
• Answer questions 7-12 and 21-24