Every organism at one time or another has to learn to adapt to a new
environment. This is why evolution of organism is needed in order to survive
changes to its environment, such as the case of the flightless birds. For one
reason or another over a period of 100,000 years the need for wings was
unnecessary to their survival. There could be many reasons why the birds evolved
to be more adaptable to their environment. A small population of birds would
have to replenish and start a new population. In all populations there are great
reproductive potential to replace numbers and expand the number of population.
After their population grew there would be a leveling off of the population once
it reached a stable size. The birds' population would become stable due a lack
of food to support every bird in the population, along with predators helped to
contribute to keeping the population stable. After being on the island a while
the birds' population would start showing a variation in different traits. Such
things as color, wing size and overall size may vary, due to predators and the
terrain of the environment. Eventually the birds evolved to the point where the
use of their wings was no longer needed, as a necessity to survive. The
adaptation could have been because flying itself took to much energy, so to
conserve food they didn't fly too much. The bird's food also could have been
close to the ground and there was no need to really fly. Another thing could
have been that it was hard for predators to catch the birds if they stayed in
think under brush or traveled along the ground. For whatever reason the birds
didn't need their wings this trait was passed of from generation to generation.
The reason this trait was passed on was because it helped the survival of these
individual birds. They were able to reproduce and pass these traits through
heredity.