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Sources of Variation
- The exchanging and recombining of genes during meiosis and
fertilization result in a great variety of
new possible gene combinations from that of the parents.
- Mutations are random changes in the
genes or DNA of sex cells may result in new gene combinations creating
variation in the offspring formed from
these.
Only
mutations that occur in sex cells can be passed on to the
offspring. Mutations which occur in other cells can be passed on to other
body cells only. The experiences an organism has during its lifetime can
affect its offspring only if the genes in its own sex cells are changed by the
experience.
Variation
and Evolution
Evolution
is the consequence of the following factors:
- the potential for a species to increase its numbers
- the genetic variability of offspring due to mutation and
recombination of genes
- a finite supply of the resources required for life
- the ensuing selection by the environment of those
offspring better able to survive
and leave offspring.
Some
characteristics give individuals an advantage over others in
surviving and reproducing, and the advantaged offspring, in turn, are
more likely than others to survive and reproduce. The proportion of individuals
that have advantageous characteristics will increase.
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An Example of Variation Driving Natural Selection |
| Natural selection favors longer necks
better chance to get higher leaves. Favored character
passed on to next generation. |
| Original group exhibits
variation in neck length. |
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After many generations,
the group is still variable, but shows a general
increase in neck length. |
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The
variation of organisms within a species increases the
likelihood that at least some members of the species will survive under
changed environmental conditions.
The
great diversity of organisms is the result of billions of
years of selection
for favorable variations that has filled available niches of
our planet with life forms.
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