There is no question that the diversity
of life is enormous, and measures of this biodiversity
are based on species.
It's easy to see that Homo sapiens is a completely
different species from Danaus plexippus (monarch
butterflies). No problem!
But "species" are sometimes hard to define.
Species that are very closely related to each other
can be so similar as to defy differentiation.
That's because species themselves are wrapped up in
the ongoing process of evolution, and they exist on
a temporal and spatial continuum. Click here to learn
more about drawing
boundaries between species.