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preparative time. If the adaptive degree of an organism is twice that of another
one, it will reproduce twice as many offspring as another one per unit time. The
representation of adaptive degree makes programs be capable of showing useful
behavior rather than simply self-reproducing.
3. Reproduction
It means self-replicating and producing the offspring. The reproduction in Avida
is accomplished through the four processes shown below:
(1) Allocate new memory to the subprogram;
(2) Copy father program into new memory by copying the commands one by
one;
(3) Divide the program into father program and subprogram;
(4) Place the subprogram in the grid.
4. The selection of placing methods
After the birth of an offspring, which grid should be chosen to place it around the
father? We have the following options:
(1) Choose the empty position: This is a highly limited method of reproduction,
but when dying is started, it is a generally effective method. In this mode,
cells are forbidden to kill each other, and only the newly born living beings
are allowed to move into empty cells.
(2) Choose the oldest one: This is the default method in Avida. The living beings
around the father body (including the father body itself) will be assessed, and
the oldest one among them will be deleted. If there exist several living beings
with the same degree, choose and delete one in the oldest units at random,
and then wait for the arrival of new living beings.
(3) Choose the maximum age/index: This placing method relatively benefits the
living beings with higher indexes, and helps to stimulate the living beings to
study the extra special skills as an encouraging method.
(4) Choose at random: Choose the son living being from the father and its eight
neighbors at random. Because before they have any offspring, about half of
these living beings will be substituted, so this kind of method is bad for
evolving.
