  A sufficiently advanced extraterrestrial civilization can send out a swarm of
self-replicating probes for space exploration. Given the fast-growing number of
such a probe, even if there is only one extraterrestrial civilization sending
out such probes in the Milky Way galaxy, we should still expect to see them.
The fact that we do not consists part of the Fermi paradox. The suggestion that
self-replicating probes will eventually mutate to consume their progenitors and
therefore significantly reduce the number of total probes has been investigated
and dismissed in the literature. In this work, we re-visit this question with a
more realistic Lotka-Volterra model, and show that mutated probes would drive
the progenitor probes into "extinction", thereby replacing them to spread
throughout the galaxy. Thus, the efficiency of mutated probes in reducing the
total number of self-replicating probes is even less than previously thought.
As part of the analysis, we also suggest that, somewhat counter-intuitively, in
designing self-replicating probes, one should not program them to stop
replicating when sufficient mutation causes the probes to fail to recognize the
progenitor probes as "self".
