SOME primitive organisms may be impossible to divide into species.
Take, for example, the genus Halorubrum, salt-loving, bacteria-like organisms that are part of the group known as . Thane Papke of the University of Connecticut at Storrs and his colleagues compared genetic sequences of Halorubrum from three different ponds, two in Spain and one in Algeria.
While there were plenty of genetic differences, the archaeans swapped genes so prolifically that there were no clear boundaries enabling them to be assigned to distinct species (). The same may be true of…
