No creature is an exact copy of its parent. Any part of it
might be slightly bigger or smaller or differently shaped. As the creature
breeds it passes traits on to its offspring. As various traits combine they
become exaggerated, such as two tall parents having taller children and two
smaller parents having smaller children.
If all the most nutritious food in a supermarket was moved to the highest
shelf and the shelves were impossible to climb it would be the tallest children
in the next generation who would be the best fed, those with the tallest
parents.
If the lower shelves were emptied and the unit toppled over scattering the
little remaining nutritious food onto the floor it would be the smallest who
would be most satisfied, their needs being the least, and only the most
flexible of the tall would eat at all.
If the supermarket were to run out completely it would be those with the
stamina to reach the next and the speed to get there before the crowds who
would eat.
It can be misleading to say a creature evolved to have a long neck to eat
the highest fruit to survive. This wrongly implies a purposeful advance.
It is clearer to say that of the range of neck lengths that had existed it
was the shorter ones that died out because they could no longer reach the fruit.
Which is just a natural filtering out of the least efficient when times get
tough.
It will generally have been a significant environmental change causing a
scarcity of food that will have brought about the natural extinction of any one
version of a species if it cannot compete with any other version or species
sharing the food resource.
Mankind has also brought about the extinction of many species though its
own action and through the accidental or intentional contamination of separate
balanced ecosystems with species or diseases from elsewhere.
The deepest areas of the ocean are the places where changes to the climate
on the surface of our planet has had least effect and where the environment
still supports creatures that have remained successful in very early versions.
On the surface of the earth the swamp seems to have been the most
consistent environment, always existing somewhere as the perfect home for
crocodiles and alligators, they being among the oldest versions of any
creatures we can see easily today.
