The<unk>  <unk>  of any set of organisms is the most<unk>  individual from which all organisms in the group are directly descended.  The term is most frequently used of humans.
The<unk>  of a set of individuals can sometimes be determined by referring to an established pedigree.
In general, however, it is impossible to identify the specific<unk>  of a set of individuals, but an estimate of the time at which the<unk>  lived can often be given; such estimates can be given based on DNA test results and established mutation rates, or by reference to a non-genetic genealogical model.
The term<unk>  is usually used to describe a<unk><unk>  of individuals within a species.  It can also be used to describe a<unk><unk>  between species (i.e. the species founder).  To avoid confusion, last<unk><unk>  (LCA) or the equivalent term concestor, coined by Richard Dawkins, is sometimes used in place of<unk>  when discussing<unk> y between species.
Most recent common ancestor
Biased sample
Cumulative incidence
Mean lifetime
Incidence 
Point prevalence
Period prevalence
Selectable marker