AQA GCSE- Biology 2.8

Additional Science, biology 2.8; speciation, old and new species

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B2.8 Old and new species
Evidence for early forms of life comes from fossils
Fossils are the remains of organisms from many years ago, which are found in rocks
Fossils may be formed in various ways:
from the hard parts of animals that do not decay easily e.g. bones, shells or teeth
from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent e.g.
insects in solidified amber resin (no air/microbes can get in), glaciers or permafrost ground (too cold for decay
microorganisms to function) or very acid peat bogs (pH too low for microbes to function, the bones dissolve rapidly but
flesh and human clothing/animal coats can be preserved in a sort of 'mummified' state)
When parts of the organism are replaced by other materials as they decay - e.g. mineralisation from surrounding
sediments of sand or shale layers
As preserved traces of organisms, e.g. footprints, burrows and rootlet traces
Many early forms of life were soft-bodied, which means that they have left few traces behind, of the few most have been
destroyed by geological activity
We can learn from fossils how much or how little different organisms have changed as life developed on Earth
Extinction may be caused by:
Changes to the environment over geological time - e.g. think of plate tectonic movement over millions of years from
warm equatorial areas to cold arctic areas of the Earth's surface
New predators - one species can consume another; humans have been responsible for many extinctions by over hunting
New diseases - e.g. an animal's immune system unable to cope with a new mutant bacteria or virus
New, more successful, competitor for food invading a particular habitat
A single catastrophic event, e.g. massive volcanic eruptions, collisions with asteroids (huge impact 65 million years ago
may be responsible for the extinction of dinosaurs), onset of an ice age
New species arise as a result of:
A species is a group of similar organisms that can interbreed to give fertile offspring
Speciation is the development of a new species and can happen when populations of the same original species become so
different (genetically) that they can no longer interbreed to give fertile offspring
o Speciation can occur via isolation ­ two populations of a species become separated, e.g. geographically,
o In the two geographical regions, the climate might be different, the other plants and animals may be different. So if each
population can survive, by the process of natural selection, two distinct species can evolve or one population remains the
same, but the other has to adapt to a different environment. Therefore breeding continues separately within each
distinct population - in time producing further genetic distinction
Genetic variation ­ each population has a wide range of alleles that control their characteristics
Natural selection ­ in each population, the alleles that control the characteristics which help the organism to survive are
selected and passed on to the next generation


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