Punctuated equilibrium is the idea that evolutionary
changes can happen in fits and starts, rather than slowly and continuously. The notion
of "punctuated" can be thought of as a kind of metaphor, with punctuation being
something that stops a process, just like a period stops a sentence. Imagine birds, for
example, that go through a period of drought. Those that have a slight variation in
their beaks that allow them to find food more easily will survive and pass on this
trait. Those that have another kind of beak will not survive. Thus, in one generation,
a dramatic change occurs, and there might be no further changes for many generations,
unless and until there are external forces to created another punctuated change. In a
continuous evolutionary situation, there would be tiny, incremental changes that would
take many generations to "settle" into a useful
trait.
Another way to look at this is to think of that
game in which you change one letter of a word, then the next person changes one more
letter, and this continues until there is an entirely different word. That would be
continuous evolution. However, if you picture a word in which several letters are
changed to get a new word, that would be punctuated
evolution.
Darwin's theory of evolution is by no means
disproved by the idea of punctuate evolution, in my opinion. His theory, simply put, is
that all living creatures have evolved over millions of years, in response to their
environments, as opposed to having been put on this earth in their present forms by some
divine creator. Today, we have more information and better tools that confirm the idea
that this sometimes happens more quickly and dramatically than Darwin
realized.
I have provided links for a good article on
evolution and for a good article on Stephen Jay Gold.
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