One male was aggressive at capture but later displayed
pacifistic behavior like the others. Another male displayed
1 hour of aggression out of several days of pacifistic behav-
ior. In sum, the pacifistic behavior was tested five times in
small containers for hours and five times in aquaria for 1
week and more. In all cases, pacifistic behavior was the rule,
with only the two short-term aggressive exceptions.
Under similar experimental conditions, we conducted a
control experiment with eight Israeli S. ehrenbergiof 2n
60 (S. judaei), a species with a relatively high level of paci-
fism (Nevo et al. 1986). Immediately upon insertion into
the aquarium, the Israeli mole-rats started fierce fighting in-
volving attacks, biting, and excited agonistic behavior. This
encounter resulted in wounding six out of eight animals
during the 10-minute experiment, which was terminated to
prevent mortality. The control experiment represents the
usual behavior obtained in more than 1,500 pairwise com-
bats of mole-rats from twelve populations (Nevo et al.
1986). The Egyptian pacifistic behavior is outside the range
of all 1,500 tests. The probability of obtaining such an out-
of-range result in three different samples, by pure chance,
is p 10 ^9. Thus a dramatic and significant behavioral
difference exists between Israeli and Egyptian S. ehren-
bergimole-rats, separated by the Sinai Desert. The Egyp-
tian mole-rats displayed amicable aggregative behavior well
beyond the normal range of Israeli mole-rats. The results
and statistical procedure appear in table 1 of Nevo et al.
(1992).
Social evolution in Spalax
In all of our field and laboratory observations and experi-
ments the northern Egyptian mole-rats behaved pacifisti-
cally. A tendency to aggregate also occurs, and this pattern
suggests a potential for future evolution of social behavior.
In contrast, however, our field observations suggest that
almost all animals are solitary. Aggregative behavior may
depend on certain food or temperature conditions. In our
laboratory experiments, aggregation was maximal in open
aquaria, where heat dissipation was larger than in the maze
or field. Thus it appears that while this animal usually lives
solitarily, it may allow neighbors to enter its territory at
times of low temperature. Critical experiments could deter-
mine which stressor as well as any other causes may lead to
aggregation and thereby possibly open the way to a social-
like phase and future social evolution.
Total pacifism in the Egyptian Spalaxisolates in the
harsh environment of the Sahara Desert is understandable
as an ecophysiological adaptive pattern leading to a meta-
bolic economy (Nevo et al. 1986; Ganem and Nevo 1996).
We suggest that the Egyptian S. ehrenbergiwas selected for
pacifist behavior in the Sinai Desert where aggressive pheno-
types were eliminated and total pacifism evolved. A desert
habitat presumably favors pacifist behavioral phenotypes
to minimize overheating, water, and energy expenditures
(Nevo and Shkolnik 1974), and the emergence of sociality
in Spalaxmay also involve defense against potential preda-
tors. The evolution of pacifism in North African Spalax
may follow the aridity – food distribution hypothesis of Jar-
vis et al. (1994), suggesting that social evolution is corre-
lated with harsh environment. Thus ecological factors and
kin selection may have interacted in social evolution in
these species. In brief periods after rains the animals must
cooperate to locate food patches. By living in groups, arid
zone mole-rats can utilize better burrowing conditions. Ac-
cording to this hypothesis, subterranean rodents that in-
habit xeric areas with dispersed patchy food and unpre-
dictable rains can neither expand their tunnel systems nor
disperse from them.
Social behavior in subterranean mammals is relatively
rare, occurring primarily among some South American cte-
nomyids (Lacey 2000), but particularly in the truly social
endemic African bathyergids (Jarvis and Bennett 1990; Jar-
vis et al. 1994; Sherman et al. 1991; Burda 1999; Bennett
and Faulkes 2000). We have now found some convergence
in social evolution. Future critical studies are necessary to
test the nature, pattern, and degree of social evolution in the
field for all Egyptian and Libyan isolates of Spalax ehren-
bergiin North Africa.Recent Speciation of the Spalax ehrenbergi
Superspecies in the El-Hammam Isolate
in Northern EgyptWe propose that the small northern Egyptian isolate of S.
ehrenbergifrom El- Hamman, near El Alamein, separated,
presumably 10,000 –25,000 years ago, from the Israeli com-
plex (Lay and Nadler 1972) and evolved into a new species
(Nevo, Simson, Heth, Redi, and Filippucci 1991). Our con-
clusion is based on the following evidence: (1)Karyotype:
the diploid number of the El-Hammam mole-rats is2n60,
but the karyotype differs in morphology, as deduced from
banding, from that of the Israeli 2n60. (2) Genetic dis-
tance:The Nei genetic distance of the El-Hammam Egyp-
tian isolate from the Israeli 2n60 is D0.061, larger
than the genetic distances among the four Israeli species
(average 0.035; range 0.002 – 0.056). (3) Morphology:The
Egyptian mole-rats differ in cranial and bacular morphol-
ogy from the Israeli Spalax judaei, 2n60, and (4) Be-
havior:The El-Hammam population has evolved a totally
pacifistic behavior displaying at least initial patterns of so-
cial evolution.
We propose that the El-Hammam Egyptian isolate is aEvolution of Pacifism and Sociality in Blind Mole-Rats 301