Transcript Theories of Evolution

Theories of Evolution
Students know the theory of evolution
That there is evidence that evolution
has taken place.
Some of the other theories of how life
began on Earth
HSW – interpret evidence relating to
evolutionary theory
HSW – learn that the credibility of the
evidence may increase if it is
consistent with existing ideas or
scientific consensus
Learning Outcomes
• All students know that the theory of evolution is the
one accepted by most scientists
• Most students can state the theory of evolution and
describe some of the evidence that evolution has
taken place. They have some understanding of why
Darwin’s theory of natural selection was only
gradually accepted.
• Some students can identify the differences between
evolution and other theories. They can suggest
reasons for the different theories explaining life on
Earth
Theories for change
Dates of theories: Lamarck (1809), Cuvier (1825) &
Darwin (1844, but not published until 1859)
.
Cuvier
(1769-1832)
Darwin
(1809-1882)
Theories for change
Dates of theories: Lamarck (1809), Cuvier (1825) &
Darwin (1844, but not published until 1859)
In the early 19th century:
1 The generally accepted date of the creation was 4004 BC.
2 The Church taught that the Bible was the literal truth.
3 More was known about variation and adaptation of animals and
plants than ever before.
4 Many accepted that fossils were the remains of organisms from
the past.
5 Scientists saw that different layers of rocks contained
different sets of fossils.
6 Some taught that fossils showed that some living things died out
and were then replaced by others.
7 The Earth’s crust is constantly changing . why not living things?
8 Small changes in living things had been observed.
Lamarck’s theory of evolution
Jean-Baptiste Lamarck (1744-1829) was a French botanist
who believed that species evolved because they inherited
traits acquired through the over or under-use of body parts.
How would this theory explain a
giraffe’s long neck?
The short-necked ancestors of
modern giraffes needed to reach the
leaves on tall trees when food was
scarce.
Over their lifetimes these
giraffes stretched their necks; a
trait which was then passed on
to their offspring.
Lemarck’s theory of acquired
characteristics
• Every type of animal evolved from
primitive worms.
• He believed that the change from worms
was causes by the inheritance of acquired
characteristics.
• Useful changes in the parents are passed
on to the offspring
( so body builders all have children with
huge muscles?)
Who was Charles Darwin?
Darwin’s theory of evolution
The British naturalist Charles Darwin
(1809–1882) later suggested a more
persuasive argument for evolution.
Darwin proposed that evolution took
place through natural and sexual
selection.
Darwin developed his theory of
evolution after noticing close
similarities between certain fossils and
the adaptations of modern day animals
he saw during his round-the-world
voyage on the HMS Beagle.
Darwin’s theory of evolution
• That all living organisms have evolved
from simpler life forms.
• This evolution comes about by a process
of natural selection.
• Only those most suited to their
environment survive – the survival of the
fittest
Natural selection
How the giraffe got its neck
How does Darwin’s theory explain a giraffe’s long neck?
Due to natural variation, the ancestors of modern
giraffes would have had necks of different length.
Giraffes with longer necks would have been able
to reach more food than those with shorter necks.
As a result, the long-necked giraffes were
more likely to be healthy and live to produce
more high-quality offspring.
This, in turn, would increase the chances of
their long-necked characteristic (an adaptive
trait) being passed on to future generations.
Galápagos finches
In the Galápagos, Darwin noticed that different islands had
different types of finches, with different types of beak.
 Some finches had strong and claw-like
beaks, suitable for crushing seeds.
 Other finches had thin and delicate beaks,
suitable for picking insects from holes in
the ground.
Darwin thought all the finches could have evolved from one
type of finch that came from the mainland.
Natural variation meant that some finches had slightly
different beaks. These finches would have been able to eat
different types of food and avoid competition. They would
therefore have survived and passed on their genes.
What happens when habitats change?
Adaptive evolution ensures that individuals within a species
have traits allowing them to survive and reproduce in their
habitat.
If the habitat changes, however, successful traits can
become a disadvantage.
For example, if global warming caused
Arctic snow to melt, brown rabbits may
be better camouflaged and so more
likely to survive than white rabbits.
Individuals that fail to reproduce, compete effectively for food
or survive against new predators will eventually die out. If the
last individual of a species dies, the species is extinct.
New theories are
new, creative ideas
To get a theory accepted,
you must explain how it could
happen (a mechanism)
A good theory may not
always be accepted, even
when the evidence is.
Creationism
• This is where people believe that God
made the world in seven days.
Intelligent design
• What is the theory of intelligent
design?
• The theory of intelligent design holds that
certain features of the universe and of
living things are best explained by an
intelligent cause, not an undirected
process such as natural selection.
Is intelligent design incompatible with
evolution?
• It depends on what one means by the word
"evolution." If one simply means "change over time,"
or even that living things are related by common
ancestry, then there is no inherent conflict between
evolutionary theory and intelligent design theory.
• However, the dominant theory of evolution today is
neo-Darwinism, which contends that evolution is
driven by natural selection acting on random
mutations, an unpredictable and purposeless
process that "has no discernable direction or goal,
including survival of a species."
• It is this specific claim made by neo-Darwinism that
intelligent design theory directly challenges.