Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

The Microbial Self 89

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

interconnected network of cytoplasm. The network is highly dynamic,
with cytoplasm continuously flowing from one part to another. In this
manner the cell crawls slowly from one place to another in search of
food. If food is scattered in several locations, as in the case of oat flakes
placed on a surface, the cellular network positions itself within hours
to maximize contact with the food sources. To do this the cell connects
the multiple food supplies along the shortest possible path, even find-
ing the best way through a maze. Surprisingly, the networking simulates
a purposefully designed mathematical model for a railway system. The
mechanism for this self-optimization algorithm is yet to be explained.^14
Physarum slime mold is also capable of forming spatial “memory” in
navigating a U-shape barrier to reach a chemo-attractive goal even in the
absence of a gradient guidance (Fig. 4.4). It turns out that as the slime
mold forages, it avoids areas that contain extracellular slime, which the
mold leaves behind as it moves. It uses a chemical feedback as “memory”
of the past.^15

Fig. 4.4. Navigation of Physarum polycephalum around a U-shaped trap. The
multiple short arrows indicate the path taken by the organism to reach the goal (food
source). [See Note 15; courtesy US Natl. Acad. Sci.]