B3 Life on Earth - Evolution

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B3 ­ Life on Earth ­ Answers
1. The basic theory of evolution is that all the different species on Earth have evolved from simple life forms that could
copy or replicate themselves. These simple life forms first developed more than 3500 million years ago (the Earth is
about 4500 million years old). The oldest evidence for life in Britain is of the remains of billions of single-celled
organisms that once lived along the edges of an ancient ocean near the Scottish island of Iona, dating to nearly 3000
million years old. These simple life forms later developed certain traits including cellular structure and genetic code ­
shared by all organisms' today indication that all existing organisms must share a common ancestor. The conditions
then were very different to now, but they must have been just right for life to grow, if they had different the results could
have been different. During that time there has been a large number of species living on Earth, many of which are now
2. Evidence for evolution is provided by:
Fossils which are important as evidence for evolutions, however only a very few living things end up as fossils
because conditions have to be just right for fossils to develop, therefore there are gaps in the fossil record.
The comparison of genes from living things, which helps scientists to work out where different species fit on the
evolutionary tree (classification) - showing how closely related different organisms are and whether they came
from a common ancestor. E.g. humans share 98.8% of chimpanzee DNA but mice share only 85% of chimpanzee
Distribution of Organisms ­ many mammals all over the world share features. Examples of this can be clearly
seen in South America and Africa where lions are similar to leopards. The differences between organisms make
them two different species, but their similarities support the idea that they arose from a common ancestor.
Homologous and Vestigial structures ­ The limbs of amphibians, reptiles and birds are all based on the same
design. This suggests they may have all developed from a common ancestor.
3. Fossils can be formed from:
Hard parts organisms that don't decay easily
Parts of animals and plants which haven't decayed because one or more of the conditions needed for decay
were absent, e.g. oxygen or moisture
Soft parts of organisms which can be replaced by minerals as they decay. This can preserve traces of footprints
or burrows.
4. There are two possible origins for these replicating molecules:
They were produced by conditions on Earth at the time (harsh surface conditions or in deep sea vents). Deep sea
vents on the ocean floor contained minerals. When the hot water from the springs meets cold sea water, minute
bubble of iron sulphide and other chemicals could have acted like tiny cooking pots, forming a thin layer of fatty
protein on the inside of bubble ­ the first cell membranes.
They came from somewhere else, where life had developed in water soaked rocks beneath the surface of a planet.
An external source, which life arrived on, e.g. a comet hitting Earth. This is believed because early Earth was too
hostile for life to have started here.
5. Species: Individuals in a population who can interbreed to produce fertile offspring. Species that breed with other species
produce offspring known as hybrids that are often infertile.
6. Variation can be caused by both genes and the environment. But it is only variation caused by genes that can be passed
on to the next generation.
7. The Process of Natural Selection:
Individuals show variation, i.e. differences due to their genes. This is because of random mutations that occur in
There's competition for food and mates. Also disease and predators keep population sizes constant in spite of
many offspring.
The variation within a species enables some of the individuals to be better adapted to the environment of the time
than others. Those individuals can survive better are able to live and reproduce. This is `survival of the fittest.'
Survivors pass on genes to their offspring resulting in an improved organism evolving over generations ­ this is the
process of evolution. As long as the environment stays the same, the individuals with these alleles will be the fittest
individuals. However if the environment changes different individuals with different alleles may become the fittest.
8. The Process of Selective Breeding:
Individuals show variation due to differences in their genes.
Humans choose the individuals with the features they want
These are the plants or animals that are allowed to breed.
They pass their genes on to their offspring so that more of the next generation will have the chosen feature. If
people keep choosing the same feature even more of the following generation will have it.

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The Peppered Moths as an example of natural selection:
Peppered moths are naturally pale and speckled so they are well camouflaged against silver birch trees. However,
some moths were naturally darker due to their genes ­ this is variation within a species.
Darker coloured and paler moths had to compete for food.
During the industrial revolution air pollution discoloured the trees with soot. Darker moths were better camouflaged
against the blackened trees and buildings. Paler moths were seen by birds and eaten.…read more

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An involuntary or reflex nervous action, which does not require the involvement of the brain. Reflex actions are rapid
and we don't need to think about them.
Removing your hand from a pin is an example of a reflex nervous action:
receptor detects a stimulus i.e.…read more

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Having a larger brain would give individuals an advantage making them more likely to survive.
At first, scientists also thought that the development of big brains allowed the development of being able to stand up
right. They needed more evidence to agree with the explanation to increase confidence in it and prove that the
explanation was correct.
However, fossil evidence found later suggests that walking upright came first because the animal found had a small
brain but walked upright.…read more

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Mass Extinctions: When species disappear in a relatively short time. These occur when environmental change happens
so quickly that animals and plants can't adapt fast enough.
28. Human activity has been responsible in the extinction of some species because:
The introduction of new predators or competition
Industrial activities that cause global warming
Deforestation clears areas, increases CO2 levels and altars the carbon cycle.
29. Humans cause extinction of species directly by killing them through hunting etc.
E.g.…read more


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