Download Evolution and Inheritance: Natural selection

Evolution and Inheritance: Natural selection
Objectives
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Recognise that animals and plants have changed over time and that fossils provide
information about living things from Earth’s past.
Identify adaptations in living things and see that adaptation may lead to evolution.
Plenary
Remind pupils that two animals can produce offspring which are similar but not identical. A pair of
Arctic hares produce two offspring: one with cream fur and one with white fur. Which hare is most
likely to survive in its snowy habitat?
Ancient fossils
Show the pupils some real fossils, or photographs of fossils. They may be able to recall that
fossils are formed when dead organisms are trapped in rock. How long ago did they die?
(Likely to be tens or hundreds of millions of years old). These lengths of time are difficult to
comprehend.
ACTIVITY: Ask pupils to stretch their arms outwards and imagine they are a 5 billion year
long timeline: their left fingertips are the beginning of Earth and their right fingertips are the
current day. The very simplest (single cell) life forms started to exist around their left elbows.
Around their right wrists, more complicated life forms which could form fossils started to
develop. Along their right fingers are the dinosaurs (around 100 million years ago). The last
half-millimetre of their right fingertips is all of human history.
Pupils must note:
By looking at fossils, we can see how living things looked in Earth’s history.
Evolution by natural selection
Between generations of living things, some random changes (mutations) appear. Some of these
changes are useful, such as the white fur on the Arctic hare. Animals and plants with these useful
characteristics are more likely to survive and produce offspring with the same characteristics. This is
natural selection.
Living things change over millions of years, too slow for us to watch. To see how animals and plants
have changed we have to look at their fossils. Show the pupils images to demonstrate the evolution of
the horse. How do we know what the ancient horses looked like? How does the modern horse look
different from the earlier horses?
Pupils must note:
Living things develop adaptations to survive. This can cause change over long periods of time. This
process of change is called evolution.
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Ideal adaptations
Living things become better at survival generation after generation. Over millions of years they
evolve. Thick fur, excellent vision or colours for camouflage may help animals survive. Pupils should
think of a characteristic of their favourite animal (not domestic animals as they have undergone
artificial selection) which helps it survive in the wild.
Pupils should recognise that evolution does not ‘plan ahead’ so living things are not perfect. For
example, humans have appendices that we do not need.
Using the worksheet, pupils should match the survival situations with the relevant adaptations that
may appear in animals and plants.
Cold habitat: thick fur. Hot desert: stores water. Fast predators: run quickly. Muddy swamp: brown
skin. Leaves in tall trees: Long legs and necks.
Possible extra-curricular questions
Where do new characteristics come from?
New characteristics come from random mutations appearing in the genetic material of offspring.
These mutations in the offspring may be favourable (sharp teeth, muscular legs) or a hindrance.
Useful mutations may be carried on to the next generation.
How did humans evolve?
Humans are primates. Primates emerged in the age of the dinosaurs, around 85 million years ago. 20
million years ago, the Great Apes appeared and some stood on two legs. About 2.5 million years ago,
‘Homo’ evolved – the genus that all humans (not just Homo sapiens) belong to. An early human,
Homo habilis, used basic tools and had brains the same size as chimpanzees. Over a million years,
brain capacity increased, as intelligence helped them to survive, and they began to resemble modern
humans. Modern humans (Homo sapiens) appeared between 400,000 and 200,000 years ago and is
the only species of Homo left alive today.
How did flight evolve?
This remains uncertain and there are several possible theories as to how flight developed. Some
scientists propose that flight arose from predators diving down on their prey from a height and that
wing-like flaps developed to help them stay in the air for longer. This fits the fossil record for the first
bird (or half-reptile, half-bird), archaeopteryx.
Can we force animals and plants to evolve?
In artificial selection, we choose animals or plants with favourable characteristics and force them to
produce offspring with the same characteristics. Examples include fancy pigeons, heavy livestock or
dog breeds, adapted for different jobs.
What will humans evolve into?
This is difficult to know because evolution occurs very slowly. Humans have no predators to escape
from and use technology to keep us well-fed and safe, so we are under less pressure to survive.
However, humans are sometimes forced to develop characteristics, such as resistance to diseases or
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ability to digest certain foods. Some propose that humans will continue to grow taller, although this
may be due to better nutrition, not due to natural selection!
Why have some animals evolved to be beautiful or cute?
Many animals develop beautiful appearances, songs or behaviours in order to attract a mate; this is
known as ‘sexual selection’. Adaptations due to sexual selection include: a peacock’s tail feathers, a
blackbird’s song, a whale’s song or a booby’s blue feet. Some evolutionary biologists suggest that a
‘cute’ and infantile appearance in some animals provokes a nurturing response in fully-grown
animals of the same species, prolonging survival.
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