Re: Would evolution differ greatly on other similiar planets?

Kristina:

The short answer is "no one knows." Because all life on Earth is related
(indicated by our common genetic code), we have exactly one example of an
evolutionary "tree." Maybe some time in the distant future we will have
detailed information about dozens of independently evolved such trees. We
can make some educated guesses, however.

Certain factors constrain what kinds of life forms can be successful, and
so there should be some broad similarities between life on Earth and life
on other Earthlike planets. For instance, everything we know about
chemistry indicates that carbon-based life is the most likely on Earthlike
planets. This is because of the versatile bonding capabilities of the
carbon atom (see any college-level chemistry book for more details).
Similarly, water has been called the Universal Solvent because of its
physicochemical properties, and on an Earthlike planet with liquid water,
water is going to be heavily involved in the evolution of life because it
mediates so many low-temperature chemical reactions. 

Some other things are a little more speculative. There are basically two
successful visual systems on Earth: binocular vision like ours and
multi-ocular compound vision like that of most insects. Vision is probably
going to be important on any Earthlike planet, and so at least a large
number of the larger animals ought to use a visual system like one or
another of the two I mentioned. Similar arguments could be made for the
other senses. However, we cannot really expect detailed similarities, such
as reptile-like critters, mammal-like critters, and so on. There are many
many ways to make a living as an animal, as a cursory stroll through any
zoo or natural history museum makes very clear. And the more you learn, the
more surprises you find. If life on Earth exhibits the bewildering variety
that led a sober paleontologist to name one genus Hallucigenia, and
produced fossils that we still can't identify even at the kingdom level, we
should expect other planets to provide even more surprises. There are wasps
that mate in the egg sack and the males never leave it. I could go on and
on. The point is, the possible ways to make it as a living organism are
pretty close to limitless. Evolution on other planets is not going to
produce animals or plants that are very much like those we see on Earth.
There will be some similarities, but more differences. 

This creates a problem for the would-be world builder, because you don't
have the resources Mother Nature had. You might like to create new and
believable creatures but this could be an impossible task. Most writers
take this approach. They find some really unusual Earth creature,
preferably one that is not known to the average person, and they base an
alien on it. For instance, Alice Sheldon used those parasitic wasps that
put their eggs inside the bodies of living spiders as a model for alien
humanoids that preyed on humans. This method has the advantage that your
alien is automatically believable, because its model is a real living species. 

I suggest that you start reading science books. If you want insectoid
aliens, read about insects and other arthropods. If you need volcanoes,
read about vulcanology. You will get some good ideas from fiction as you
learn more about reality.

Another possible approach is to read the work of expert inventors of alien
species. Greg Bear, Fred Pohl, and Larry Niven are three who have put a lot
of careful thought into inventing believable aliens. There are many more
writers who have done the same.  

If you would like some more help with this kind of question, you might want
to visit www.speculations.com/rumormill.
 Go to the "The Expert Is In" topic. This bulletin board is a resource for 
SF/fantasy/horror writers, and you will find some very helpful people there.

David Kopaska-Merkel
Geological Survey of Alabama
PO Box 869999
Tuscaloosa AL 35404
205-247-3695
davidkm@gsa.state.al.us
www.gsa.state.al.us