Lecture 12: Threshold 5—Life
Now we focus on life’s astonishing capacity to change, so as to generate
new levels of complexity. How does life adapt? The key is the synergistic
way that metabolism, reproduction, and adaptation work together. The
metabolism of living organisms supplies the energy needed to maintain
their complex structures. Reproduction allows them to copy structures that
work. Adaptation enables living organisms to tweak their structures so as to
explore new ways of extracting energy from their environments. Through
adaptation, living organisms are constantly exploring the possibilities of
their environment.Though there seems to be no intrinsic drive toward greater complexity, some
adaptations will inevitably be more complex than others, which is why, over
time, the upper level of complexity
has slowly increased. Of course,
more complex organisms will
need more energy, so they will
have to develop a more powerful
metabolism. For example, the ¿ rst
organisms that learned to extract
energy from oxygen suddenly had
access to new forms of chemical
energy not available to other life
forms. Clearly, adaptation is the
key. So, to explain how more complex life forms have appeared, including
ourselves, we must explain how adaptation works.Explaining adaptation proved surprisingly dif¿ cult. The most common
traditional answer was that living organisms did not change. They were
adapted to their environments because that was how their creator made them.
This explanation is present in the sacred texts of the Judeo-Christian-Muslim
tradition, and in the works of Carl Linnaeus (1707–1778), the founder of
modern taxonomy (the system by which living organisms are classi¿ ed).Yet even when Linnaeus wrote, there were good reasons for thinking that
living organisms did change. By the 18th century many fossils had been
found of creatures that no longer existed. Why should God have destroyed
his own creations? Besides, animal breeders understood that animals doOnly “inherited
characteristics” are passed
on. A fattened pig will not
necessarily produce fat piglets,
but a pig with fat parents may.