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of tunnels and produces all the babies, while the other females and the males
bring her and the babies food and defend the tunnels fi ercely. The Israeli
mole rats, separated by deserts and the Red Sea from their African relatives,
live more solitary lives, and all the females are able to reproduce.
Even though the mole rats live underground, their evolution has been
strongly infl uenced by climatic conditions in the world above. Each species
occupies a dif erent Israeli ecosystem. A species with 60 chromosomes lives
in the hot dry south, including the sandy wasteland of the Negev Desert. A spe-
cies with 58 chromosomes is found in the more climatically moderate region
around Haifa and the Sea of Galilee. And two other species with smaller num-
areas are being fought over by their human inhabitants in part because they
receive fi fteen times as much rain as the Negev. The mole rats, meanwhile,
burrow peacefully under Israel's dangerous northern border with Lebanon
and Syria, blithely ignoring the politically charged world above them.
Nevo has shown that rainfall and the permeability of the soil to oxygen
are tightly correlated with the distributions of these species. The boundaries
between the species are sharp. Matings between the mole rats at the bound-
aries produce some hybrid animals, but these hybrids are ill-adapted and do
poorly.
Chromosome dif erences probably have something to do with the bar-
rier to the free fl ow of genes between the species. Intriguingly, the zones in
which hybrids are found are relatively wide when there are few chromosomal
dif erences between the species. They are narrower and more constricted,
indicating stronger selection against gene fl ow between the species, when
the chromosomal dif erences are greater. The dif erent species of
Spalax
have
evolved through the same processes of mutation, selection, genetic recombi-
nation, and gene fl ow that are operating in Evolution Canyon.
Perhaps, given enough time, the environmental dif erences between the
north- and south-facing slopes of Evolution Canyon might be able to gener-
ate new species. Korol argues that this will not happen, because the dif er-
ences between the two sides of the canyon are not huge and gene fl ow is able
to mix the gene pools at a high rate. But I contend that if gene fl ow is reduced
further in the future, some species in the canyon might split into two.
