Travel Reference
In-Depth Information
The fermenting lifestyle is so obviously advantageous that it is not sur-
prising that fermentation of food has evolved more than once in dif erent
branches of the great tree of life. Termites, for example, are able to munch
on our houses, not because they themselves can digest wood, but because
their digestive tracts play host to thriving colonies of microorganisms. These
organisms benefi t the termites by breaking the wood down for them, but
they eventually meet the same digestive fate that awaits the bacteria in mam-
malian ruminant guts. The termites acquired this symbiotic association quite
independently of their remote relatives, the ruminants and other fermenting
mammals.
Because fermentative symbioses have often evolved independently, it
seems to have been relatively straightforward to adapt some region of one's
gut in order to provide a place for thriving microbial populations. The advan-
tage of this type of digestion is great when there is abundant food in the envi-
ronment that is available in no other way. But we do not know the genes
involved in these modifi cations of stomach anatomy.
We have, however, learned a great deal about one particular set of genes
directly involved in fermentative digestion. In the 1980s the pioneering
Berkeley molecular evolutionist Allan C. Wilson began studies that would
eventually demonstrate how these genes have been co-opted to carry out the
same task in similar ways in hoatzins and proboscis monkeys.
Wilson and his colleagues began by investigating the two main types of
ing ourselves, secrete the fi rst type of lysozyme copiously in our tears and
our saliva. It acts as an ef ective antibacterial agent, by breaking down the
tough cell walls of any invading bacteria.
The second type of lysozyme is found in mammalian digestive systems.
It is made in especially large amounts in the stomachs and foreguts of ani-
mals that live by fermentation. But this form of the enzyme is inactive when
it is fi rst secreted.
This initial inactivity is useful, because otherwise the enzyme would
destroy the busily fermenting bacteria on which the animals depend. Then,
as the mix of bacteria and food moves into the stomach's digestive chambers,
the acidity rises and the change in pH activates the enzyme. The unsuspecting
