The concept of the individual links population biology with darwinian selec
tion. In spite of its importance, the concept is used with great ambiguity.
Confusions seemingly stem from a limited analysis of the variability found
in attributes classically used to characterize individuality. Such charact
erization involves the simultaneous holding of genetic uniqueness, genetic
homogeneity and autonomy, which in turn are considered invariant attributes
. Data accumulated over the past 15 years, however, indicate that all three
characters can independently be present or absent in different types of mu
lticellular organism. Combining their respective presence or absence leads
to recognizing different kinds of individual; a realization that has ecolog
ical and evolutionary implications.