people did not die off as fast as demographers expected. But
human survival data are hard to interpret scientifically, given
the confusing effects of wars and improvements in medical
practice. It might be that the considerable benefits of medical
practice have been especially profound among the oldest old.
Human cohorts do not supply good data for scientific infer-
ence. Human data were never going to give a clear answer to
the question of the implacability of aging.
Things changed dramatically in the early 1990s when
insect cohorts were used to study mortality rates late in life.
[6;7] In caged insects, kept under good conditions, mortality
rates stop increasing in late life.  The new facts of death
reveal three phases of mortality: juvenile, aging, and late life.
In the juvenile period, mortality rates do not show sustained
increases. In the aging phase, mortality rates increase rapidly.
In the third phase of life, mortality rates are roughly constant,
though they tend to maintain a very high level. Organisms
that reach the third phase can be said to be biological immor-
tal, in that they no longer age. This is the new immortality
that I wish to introduce to discussions of the attainment of
But before doing so, I want to put the new immortality into
a general biological context. One way in which we can classify
organisms is to divide those that are always immortal from
those that have a period of rapidly increasing mortality rates
aging prior to a period of immortality. The aging species age
first and then are immortal. Immortality is thus the universal
condition of life. Aging is the less common condition. This is
a fact of enormous significance for the long-term future of the