Natural
selection has 4 processes.
Individuals looks different and have different
characteristics from another within their own species (genetic variation). Some
characteristics suits better for the environment, which has to be passed on
from one generation to the next. The humming birds with long bills will mate
with those that have that too so they'll produce offspring with long bills.
The
second process is over production of offspring. The humming birds produces lots
of offspring but only a few survives.
Another factor of natural selection is
struggle for existence, which leads to differential survival and reproduction.
There are environmental pressures, like not having enough space or food, for
example, humming birds compete fiercely for resources like nectar. Natural
selection will favor individuals that are more efficient at getting nectar and
natural selection will result in changes in wing shape which can allow them to
fly longer distance and affect the length and shape of bill for them to drink
nectar. Little changes may affect how well they feed and survive. Those who are
the fittest survives and are most likely to reproduce and pass on their
advantageous genes to their offspring. If the long bills are more advantageous
and can survive better in a particular environment, then overtime, those with
short bills will disappear because they can't survive and the entire population
would have long bills.
