Travel Reference
In-Depth Information
Even before the advent of DNA sequencing, biologists had suspected
that domestic dogs originated from
C. lupus chanco
, the same subspecies as
the cub that the boy in the village had found. The lower jaws of domestic
dogs share with the
chanco
subspecies an oddly shaped hook at the top of the
ascending part of the jaw. The hook is not found in the jawbones of other
wolf subspecies.
But such evidence is highly circumstantial—dogs could have evolved
their bony hook independently of the Asiatic wolves. We must turn to DNA
evidence to get a clearer idea of where dogs came from. Mitochondrial chro-
mosomes provide the information we need.
Mitochondrial DNA—an introduction
Because mitochondria and their DNA play a central role in our understand-
ing of how animal domestication happened, and of how our own species
evolved, it makes sense to pause for a moment to introduce the friendly little
creatures.
Mitochondria are found in most of our cells, and in most of the cells of
wolves and dogs. These tiny structures, bounded by two concentric layers
of protein-studded membrane, are all that remain of bacteria that were for-
merly free-living. Almost two billion years ago some of those free-living bac-
teria found their way inside our remote single-celled ancestors. Perhaps they
were eaten by those teeny ancestors of ours, or perhaps they simply bullied
their way into our ancestors' cells just as malaria parasites and other organ-
isms can invade our cells today. And it is quite possible that the fi rst wave of
those bacterial invaders, like today's intracellular parasites, made our ances-
tors sick.
It turned out, however, that being invaded by these bacteria yielded a fan-
tastic evolutionary payof for our distant ancestors. The payof was so huge
that it greatly outweighed any damage that the invading bacteria might have
caused. This is because our ancestors had previously, in a fi t of carelessness,
lost their ability to use oxygen for respiration. This was a really dumb thing
to do, because organisms that can use oxygen can squeeze eighteen times as
