Organisms produce more offspring than needed to maintain a constant population. Population sizes stay fairly constant.
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Give the other 2 of Darwin's observations.
Organisms within a species show variation. Offspring resemble their parents.
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What were Darwin's 3 deductions from his observations?
There's competition for survival. Individuals that are best adapted to their environment are more likely than others to survive and breed. Many characteristics are genetic and can be inherited.
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What is natural selection?
The process in which an environmental factor determines which individuals will survive. If an individual has beneficial characteristics for the selection pressure, it will survive and pass on these characteristics.
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What could be a selection pressure?
Predators- individuals adapted to escape, or avoid being eaten. Disease- individuals immune to a disease. Availability of suitable food- individuals adapted to eat the available food.
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What is speciation?
The formation of a new species from a pre-existing one.
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What would have to happen for two groups to become different species?
Need variation in original population from random mutations. Need different selection pressures to act on groups. Best adapted in each group survive & pass on good characteristics. 2 groups very different. No longer produce fertile offspring together
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What is a reproductive barrier?
Any factor which prevents reproduction between members of a species.
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What is allopatric speciation?
Where there is a physical/ geographical separation. This could be a moutain or a river.
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What is sympatric speciation?
Not due to physical separation, but barriers that occur within a population. Such as a change in courtship display, or there may be a biochemical change where the gametes are not compatible.
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In terms of evolution, why do pesticides no longer work as well?
Variation in pest species- random mutations. Pesticide is selection pressure. It kills off pests without resistance gene. Better resistant pests produce fertile offspring with resistance gene-more resistant next generation-survive, breed & pass it on
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Other cards in this set
Card 2
Front
Give the other 2 of Darwin's observations.
Back
Organisms within a species show variation. Offspring resemble their parents.
Card 3
Front
What were Darwin's 3 deductions from his observations?
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