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Evolution
and extinction
Evolution and extinction
Why have some species of plants and
animals died out?
How do new species of plants and
animals develop?
Evolution and extinction
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fossils
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evolution
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mutations
Theory of evolution
All species of living thing that exist today (and
many more that are now extinct) have evolved
from simple life forms that first developed over
three billion years ago.
Evidence for evolution - fossils
What are fossils?
– The remains of plants and animals from many years
ago.
– Found most often in sedimentary rocks.
How do fossils provide evidence for evolution?
– Fossils of extinct animals and plants can be arranged in
a time sequence.
– This allows inferences to be made about how and when
they evolved.
Fossils in the Grand Canyon
• The sedimentary rocks of the Grand Canyon are hundreds
of millions of years old.
• The Colorado River has cut a gorge through the rock 1.6
km deep.
• Rocks at the bottom of the gorge are 2,000 years old.
• Observation of the fossils in the rock layers suggests:
– fish were the first vertebrates to appear 500 million
years ago.
– reptiles appeared about 300 million years after the fish.
Fossil formation
Fossils can form in the following ways:
1. When parts of the plant or animal have been replaced
by other materials as they decayed:
•
petrifaction –being converted to stone or a stony
substance.
2. Preserved traces of plants and animals:
•
footprints
•
burrows
•
rootlet traces.
Fossil formation (continued)
3. Hard parts of animals that do not decay:
• bones, horns, teeth, tusks.
4. Parts of animals and plants that have not decayed
because of unsuitable conditions:
• mammoths trapped in ice
– too cold for decay.
• bog men found in peat
– too acid for decay.
• mummified remains
– too dry for decay.
Evidence for evolution - geography
What is Continental Drift?
– The slow separation of continental land masses as they
move on tectonic plates.
How does this give evidence for evolution?
– Africa and South America have separated.
– Some animals on these continents are similar but
different; suggesting common ancestors.
• camel
llama
• lion
jaguar
• rhinoceros
tapir
Evidence for evolution – comparing anatomy
What are homologous structures?
– Parts of bodies that have similar structure but are
adapted to different jobs.
Example of a homologous structure:
– The pentadactyl (five-fingered) limb
• amphibians - flippers
• reptiles – legs and claws
• birds - wings
• mammals.
whale – flipper
human – hand
bat – wing.
Gene mutations
What is a gene mutation?
– Changes to a gene caused by changes to the structure
of the section of DNA molecule that makes up the gene.
What causes gene mutations?
– Mutations occur naturally
– The chance of a mutation occurring is increased by
exposure to:
• radiation from radioactive materials
• X-rays or ultraviolet light
• some chemicals.
Mutations in reproductive cells
What is the effect of a mutation in an egg or sperm cell?
– As the foetus develops after fertilisation it may develop
abnormally or die at an early stage in development.
Is this kind of mutation always harmful?
– Some mutations have no obvious effect.
– Occasionally a good mutation occurs that gives an
organism some advantage in the struggle for survival.
– This good gene may be passed on to offspring.
Mutations in ordinary body cells
What is the effect of a mutation in an ordinary body cell?
– The cell in which the mutation occurred may start to
multiply out of control.
– Some of these cells may then break away and invade
other parts of the body.
– This is cancer.
This is caused by exposure to:
– Radiation from radioactive materials.
– X-rays or ultraviolet light.
– Some chemicals, particularly those in cigarette smoke.
Darwin’s theory of evolution
Charles Darwin (1809 – 1882) suggested:
– Life is a struggle for survival
• competition for food
• threats from predators
• disease
• climate changes.
– There are continual changes taking place within a
species (ie variations between individuals) caused
by:
• reshuffling of chromosomes during sexual
reproduction
• mutations.
Darwin also suggested:
– Some individuals have variations that give them an
advantage over others within their species.
– So in the struggle for survival these individuals are
more likely to survive to be able to reproduce and pass
on their advantageous genes to future generations.
– Nature selects the fittest organisms within a species and
rejects the less fit .
• survival of the fittest / natural selection.
– So good mutations help evolution.
Lamarck’s theory of evolution
Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamark
(in 1809) suggested:
– Parts of the body that are used a lot become well
developed.
– These beneficial characteristics, developed during an
individual’s lifetime, could be handed down to offspring.
• This suggests that giraffes have long necks because
individuals in each generation have stretched their
necks a little more during feeding.
Mutant microbes and antibiotics
What are antibiotics?
– Safe chemicals introduced into the body to kill bacteria.
Why are doctors reluctant to use them on too many patients?
– Bacteria produce new generations very rapidly because
of fast reproduction.
– Therefore, there is a higher rate of gene mutations.
– Chance mutations may result in the formation of
resistant groups of bacteria.
Extinction
What causes the extinction of a species?
– Evolution is a slow and gradual process of adapting to
change.
– Extinction occurs when environmental changes occur
too quickly for gradual evolutionary changes to take
place, such as:
• sudden climate changes
• pollution
• pesticides and herbicides
• disease
• introduction of a new, more successful species into
an area.