|Why do different continents have different types
of living organisms?|
|Question Date: 2017-09-15|
Great question. There are a few answers. One is
that conditions on continents can be very
different. As species evolve in different
environments, they are under different pressures.
For example, a species that survives and
reproduces well in a warm, wet environment may die
in a cool, dry environment. So two species may
even belong to the same family and share an
ancestor that was different from both of them, but
be very different from each other.
The opposite of this is when very distantly
related species end up looking similar because
they evolved in the same sort of environment. For
example, in our desert conditions in North
America, we expect to see various species of
cacti, with no leaves, sharp needles, and a
waxy-waterproof surface. In African deserts, they
have euphorbia, which have no leaves, sharp
needles, and a waxy-waterproof surface. This site:
pictures has great pictures of both.
These two different families of cacti are not
the descendants of ancestors with no leaves, sharp
needles, and a waxy-waterproof surface. They
evolved these traits independently from each
other. This is an example of convergent
Can you think of other examples of
closely-related species that have adapted to very
different environments or distantly-related
species that look alike because they have adapted
to similar environments?
Thanks for asking,
Good question! It has to do with what species
were where when they evolved, and is thus a
historical accident, but it also has to do with
different conditions in different parts of the
world, and with the ability of species to disperse
across parts of the world that they cannot live
(trees, for example, do not grow in oceans
There is a lot of research ongoing in this area
as we try to find the answer. It depends on the
species, of course - each species has its own,
unique history, but there are patterns, and those
patterns are still being studied.
Thanks for the great question.
The tectonic plates that make up the crust of the
earth move around over the course of millions of
years. As they do, the continents and oceans on
top of the tectonic plates move as well.
Eventually populations of the same species get
split up as the plates move and continents split
apart, with oceans or mountains forming in between
them. (Note this is over millions of years and
Now, when the same species is separated by a
new mountain range or ocean, evolution by natural
selection may begin to act on the two different
populations in different ways. This is because
there might be important differences between the
two locations, including the types of food
available or what predators there might be.
Different selective pressures in these
different locations therefore favor the evolution
of different traits in different environments,
and new species may even arise from this process
(this is called allopatric speciation).
The same process can happen when some members
of a species migrate to a new environment and
don’t go back, for instance from Asia into the
Americans over an ice bridge in the Arctic.
Species that made it across were acted upon by
natural selection in their new environment and
So different continents have different types
of living organisms as natural selection has acted
on individuals of species isolated from those
members on other continents. We should expect,
and we find, species that are highly genetically
related across the different continents. However,
millions of years of natural selection have led to
the evolution of different species across the
Thanks for the great question,
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