Download How a species is formed

UNIT
5
The origin of life and evolution
HOW A SPECIES IS FORMED
Biology and Geology 4. Secondary Education
UNIT
7
5
How a species is formed
1. One or more groups of organisms from a population with the same genetic make-up become isolated
A group of omnivorous birds, with thicker or thinner beaks, is
isolated from the rest on an island which has lots of seeds
(island A).
Biology and Geology 4. Secondary Education
Another group of omnivorous birds, with thicker or thinner
beaks, is isolated from the same population on an island
which has lots of insects (island B).
UNIT
7
5
How a species is formed
2. Over time, each group accumulates different genetic variations and natural selection acts on
the populations of each group
On island A, natural selection favours the genetic variations
of birds with thicker beaks, which are better suited to
breaking seeds.
Biology and Geology 4. Secondary Education
On island B, natural selection favours the genetic variations
of birds with thinner beaks, which are better able to capture
insects.
UNIT
7
5
How a species is formed
3. After a long time, the differences between the groups are so great that the two groups become
different species
In time, a species of birds with thick beaks arises on island A.
The cross of one of these birds with one from island B will no
longer produce fertile descendants.
Biology and Geology 4. Secondary Education
In time, a species of birds with thin beaks arises on island B.
The cross of one of these birds with one from island A will
no longer produce fertile descendants.