Loadstar 128 #12/q12.d81/t.darwin's bugs

Text File | 1990-01-01 | 10.7 KB | 215 lines

                           D A R W I N 'S   B U G S

     This program demonstrates how evolution can be observed within a
microscopic world, created by a computer program.   Along the way, some very
interesting lessons in survival and in ecology can be learned.

THE WORLD IN A POND

     The basic idea was outlined in Scientific American magazine in May
1989.  The world consists of a pond, which is patrolled by bugs of unknown
heritage.  As they swim around the murky bottom of the pond, these bugs
encounter random bacteria that have fallen to the bottom.  The bugs aren't
too smart, but they know they should eat the bacteria, thus gaining the
energy that they need to keep swimming.  Bugs that don't eat enough will
wither and die.  A bug that is more successful will eat a lot and get fat;
eventually it will split into two bugs, a process called fission.

SWIMMING AROUND

     The trick is for bugs to evolve so that they get better at finding
food.  Each bug has a different movement pattern: some bugs tend to swim in
straight lines, back and forth across the pond.  These bugs are called
'cruisers'.  Some bugs mostly turn in one direction, either right or left,
so they swim around in circles and are called 'twirlers'.  Other bugs that
often back up will tend to sit in one place and jump around; of course they
are called 'jitter-bugs'.

     So here is where evolution comes into it.  At the start, the pond has
many different kinds of bugs.  If a bug has a pattern that is very effective
at gathering food, then it will multiply, and soon there will be lots of
bugs with similar habits.  When the bug splits in two, the new bug gets a
slightly different pattern (a mutation).  This allows new species of bugs to
evolve and be tried out.  Eventually the most successful kinds of bugs
should do best, and gradually take over the whole pond.

     By stocking the pond and letting the bugs swim around for a while, you
should be able to see the slow evolution of more effective swimming
patterns.

THE ECOLOGY

     So which kind of bug is most likely to succeed?  Jitter-bugs do very
well at first, quickly sucking up all the food in their vicinity.  Once the
area is cleaned up, however, they run out of food and usually die pretty
fast, burning up all their energy dancing around (kind of like a disco).
The other kinds of bugs are more careful with their energy, gradually moving
around to different parts of the pond in search of food.  Both kinds of bugs
could survive.

     But there is a rule in science that only one species can survive in a
single specialized ecology: eventually, all other species have to get
squeezed out.  In our pond, the cruisers are usually the successful ones,
because they are less likely to get trapped in an area with little food.
Over time, you will usually see the bugs evolve to this kind of pattern.

THE CAFETERIA

     There is one more complication: we can create two different ecologies
in our pond!  There is one small area of the pond -- kind of like a
cafeteria -- where the program arranges for much more food to be made
available.  The cafeteria is a separate ecology, and it's one where just
about any kind of bug could survive because there's lots of food.  The
problem for the cruisers when they enter this area is that they quickly
cruise out the other side, so they don't benefit too much.  Bugs that tend
to stay put, either twirlers or jitterbugs, will do better in the cafeteria
because their pattern allows them to stick around longer.  When they stray
out of the area, however, they usually die pretty fast.

     If you choose to have these two ecological zones in your pond, then you
should be able to see two different species of bugs evolve: cruisers in the
main pond, and twirlers or jitterbugs in the cafeteria.  Keep in mind that
this evolution is completely random -- the bugs have no brains at all, and
the computer does nothing but keep score.  The results are based just on
random changes and on success in finding food.  It may take a while for the
evolution to take place, and it may come out differently each time the pond
is stocked.  Only time will tell!

     Try turning the high-density area on or off.  Within five to ten
minutes of express operation, you should see a definite change in the
evolution of the bugs.

THE PROGRAM

     The program starts out with 12 bugs, and these can multiply up to a
total of 64.  It uses a lot of information to keep track of all these bugs,
and this is available to you to observe, or to change the living conditions
in the pond.  In order to communicate the information, the program uses both
the graphic screen and the 80-column (text) screen.  You can switch back and
forth between the two screens by pressing the CVBS/RGB button on your
monitor.

     The graphic screen is used for a visual representation of the pond:
bugs are the yellow squares that move around, while food is represented by
the blue dots that don't move.  The cafeteria, if it is activated, will show
up as a high-density area roughly in the middle of the pond.  If you choose,
the bugs can leave grey trails as they move around, or you can erase or
cancel these trails.

     The 80-column text screen is used to give details on the location,
energy, and movement patterns of the bugs.  In addition, status reports can
be given on all changes, if you wish.  This screen is also used to display
menus, and to ask for user input.

THE MAIN MENU

     When the program first starts up, you will see the main menu on the
80-column screen, and you can come back to this menu anytime you want.  From
it, you have six choices: make your choice by pressing a number key.  (You
don't press RETURN after your choice).  The choices are:

  1.  Print the program controls, either on the screen or on your printer.
  2.  Change the setup.  You can vary the parameters that control the
      program before you start, or at any time while it is running.
  3.  Print out the setup and bug data.  This will list all the factors
      you can change with the setup, on your printer.  If the pond has
      been stocked, it will also list the location, energy level, and
      characteristics of all active bugs.
  4.  Run.  This will stock the pond with new bugs, and begin their lives.
      If the program has been run previously, the old bugs will be
      exterminated.
  5.  Resume.  Once the pond has been stocked, you can return to the menu,
      and the bugs will be put on hold.  Making this choice will continue
      the lives of the bugs that already exist.
  6.  Quit.  End the program, drain the pond, exterminate all bugs and
      return to LOADSTAR.

THE CONTROLS

     When the bugs are alive, you can alter the simulation by pressing a
single letter key.  (Again, you don't press RETURN after pressing the
letter).  For a complete listing of what each letter does, choose 'Program
Instructions' from the main menu.

     There are several different modes of operation:

 -  In the three normal operation modes, the bugs will move about, feeding,
and dying or multiplying as necessary.  You will be advised of their
actions, and the table of statistics will be updated from time to time.  The
'Verbosity' function has three settings to control how many updates you get.

 -  The next mode you can select is 'Express Mode';  with this choice, you
do not receive updates, and the letter keys are not active.  This enables
the bugs to move much faster, about 50,000 individual moves per minute in
total.  With a typical complement of 50 protozoa in the community, each bug
will get to make about 1000 moves a minute (a million and a half a day).

 -  The final mode is 'Parameters';  this choice halts the bugs and displays
a list of all parameter settings.  You change any you wish, then press
RETURN to resume normal operation, or 'x' for express mode.

SOME DETAILS

     A bug's pattern is set by a series of eight numbers;  each number gives
the chance that it will turn in a certain direction.  If the first number is
large, the bug will usually go straight - a cruiser.  The next two numbers
give the chance that it will turn to the right:  either a little to the
right, or sharp right.  The next three numbers control backing up, and allow
backing up with a right turn, or straight back, or back and left.  Finally
the last two numbers control left turns.

     By checking these numbers, you can see what different kinds of bugs
have been created.  Once you become familiar with the details, you may also
want to try altering the bugs to influence evolution yourself.

     You can keep tabs on a particular bug by typing the number of the bug.
An arrow and the number will show on the 40-column screen.  To get rid of
the pointer, press 0.

SURVIVAL TIPS

     The population of the pond is governed by the food value of a meal, and
you can change this.  The program places two bacteria per cycle;  one of
these is placed in the cafeteria, if it is enabled.  Thus, the total energy
input per cycle is two times the value of a meal.  Since each bug consumes
one unit of energy per cycle, the amount of energy consumed per cycle is
exactly equal to the number of bugs.  Over the long term, energy input must
equal energy consumed.

     In theory at least, the maximum population is the amount of energy
added per cycle, ie. two times the value of a meal.  In reality, some
allowance must be made for biological inefficiencies:

Population = (E * n/c) * k
  where E = energy per meal
        n = number of meals placed
        c = rate of consumption
        k = bio-efficiency factor

Given that n=2 and c=1, and that k is about .95, the population will vary
around 1.9*E.  K is not entirely constant, increasing as E increases.  If
the value of a meal is set to 25, then the population will typically be in
the range of 45 to 50.

     Evolution will occur more effectively if bugs have a chance to multiply
and die out as necessary.  Try to keep the different parameters set so that
this can take place.  In the example above, the total population of 45 to 50
allows evolution to take place within the pond's limit of 64.  If you set
the energy value of a meal too high, then all the bugs get fat and lazy, the
population reaches the maximum level, and no evolution can occur.  On the
other hand, if you lower the food value too much, then all the bugs may die
out, or the population will become too small to maintain its genetic base.

     You may want to experiment, but you will find that an energy value of
25 per meal is about right.

SUMMARY

     This program creates an artificial ecology in your computer.  By
modifying the variables, you can observe how the computerized life forms
respond to a varying ecology.  Darwin would be intrigued!

IA
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