8th Grade
Natural
Selection
Science
Biology
Ms.Ellin
Getting started
01 Waxy monkey leaf frog
Natural selection
02 Scientific theory of natural selection
Exercise
03
Past question papers
01
Getting started
How organisms adapted
to their environment
02
Natural
selection
Scientific theory of
natural selection
How giraffes might have come to have such long necks
An imaginary story
continue…
An imaginary story
Based on the imaginary story of giraffes,
We can summarise
the theory of
natural selection
like this…
The theory of natural selection
In every species, there is variation The individuals with these
01
among individual organisms advantageous features are therefore
more likely to reproduce, and pass
04
on the genes that produce the
advantageous features to their
offspring
Some of this variation is caused by
02
differences in their genes
Over many generations, the genes
that produce these advantageous
05
features get a little bit more
Some individuals have features that
03 common, and the genes that are not
make it more likely that they will
so useful get a little bit less common
survive than individuals that do not
have these features
Some examples of natural selection
Bacteria and antibiotics
Bacteria have become resistant to some antibiotics.
Peppered moths
Variation of peppered moths in England.
Bacteria and antibiotics
Antibiotics are medicinal drugs that used to cure diseases caused by bacteria. That
are many different antibiotics, but some of them have become resistant to bacteria.
Peppered moths
Peppered moths live in England. Most peppered moths have
pale wings, but some have a gene that gives them dark wings.
Peppered moths fly at night, and spend the daylight hours
resting on tree trunks. They are hunted and eaten by birds. The
pale colour of peppered moths camouflages them perfectly
against lichen-covered tree bark.
But…in 1900, the Industrial Revolution was
taking place in England. Many factories burnt
coal, which polluted the air with smoke. The
smoke killed lichens and made the tree
trunks dark.
Peppered moths
When the tree trunks got darker, the pale moths were not camouflaged. They were more
likely than the dark ones to be eaten by birds.
The dark moths were more likely to survive and
reproduce than the pale moths. They passed on
their genes for their dark colour to their offspring.
Over several generations of moths, more and more
of the offspring inherited these advantageous
genes for dark colour. Over time, the dark colour
became more and more common. Each generation,
more dark moths were born and fewer pale moths.
Peppered moths
The proportion of dark and pale peppered moths
changed over time, when their environment changed. But
imagine what might have happened if the population had
not changed?
If the moths were still pale, then most of them could
have been eaten by birds. The population become so
small that the peppered moths all died out. The species
might have become extinct.
Extinction
03
Practice questions
Cambridge checkpoint past question papers
Past papers
Progression
1 test
Natural selection
Booklet
2 page 97
Extinction
3 May 2016,
Paper 1 Natural selection
Progression test
Thanks!
Does anyone have any questions?
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