2 April 2022 | New Scientist | 35Spare parts on demand
The mysterious process of regeneration can help us understand
life in all its complex glory, finds Simon IngsBook
What Is Regeneration?
Jane Maienschein and
Kate MacCord
University of Chicago Press
(out 6 April)
SOME animals are able to grow
an entire new body from tiny parts.
Crabs and lobsters can regenerate
lost tentacles and claws. Hydras and
some worms can regrow their heads.
We humans can replace our skin,
hair, fingernails and even our liver.
Regeneration is such a peculiar
ability that, even in science, it is
surprisingly under-researched. As
a result, there is much we still don’t
know. What Is Regeneration? is a
collaborative effort between Jane
Maienschein and Kate MacCord,
both at the Marine Biological
Laboratory in Woods Hole,
Massachusetts, to fill some of the
gaps. Together, they explore why
regeneration occurs when it does,
why it doesn’t always happen and
what the process can tell us about
the grander mysteries of birth,
death and development.
It turns out to be a seemingly
simple phenomena that, on closer
inspection, becomes far more
complicated. For instance, are we
thinking only about regeneration
of structure, about regeneration of
function or both? Is the regeneration
of the gut flora in your intestines
after a course of antibiotics or
the regeneration of woodland
after a forest fire at all similar
to regrowing a body part?
To try to pin it down, the authors
begin with a history of the study of
the subject, starting with Aristotle
and ending with Magdalena
Zernicka-Goetz’s ongoing research
on cellular signalling. Their account
pivots on the work of Thomas Hunt
Morgan (better known as a pioneer
of chromosomal genetics) and,
in particular, his 1901 book
Regeneration. Morgan, more than
anyone before or since, attempted
to establish clear boundaries
around the phenomenon, and
the terminology he came up
with remains useful.
He identified three kinds of
regeneration. The first two are
restorative regeneration, which
occurs in response to injury, and
physiological regeneration, which
describes replacement, as when
an elk moults its antlers and new
ones grow in their place. The third,
morphallaxis, refers to more
extreme cases, such as when a
hydra, cut into pieces, reorganises
itself into a new hydra without
going through the normal processes
of cell division.
The key to this categorisation is
that the mechanisms of regeneration
aren’t, as the authors put it, “a
special response to changing
environmental conditions but,
rather, an internal normal process
of growth and development”.
So here is the problem: if the
mechanisms of regeneration
can’t be distinguished fromthose of growth and development,
what is to stop everything
ceaselessly regenerating? What
dictates the process of regrowth
and why does it happen only in
some tissues, in some species
and only some of the time?
Maienschein and MacCord
argue that, to fully understand this,
we need to see regeneration as a
window into the world of biology in
general, and the complex feedback
loops that decide what grows,
divides and dies, where and when.
Far from being an interesting
curio, then, studying regeneration
can tell us much about life in
general, from a cellular level right
up to the level of ecosystems, and
inform everything from regenerative
therapies using stem cells to
ecosystem protection and recovery.
Seen through this lens,
regeneration is a far bigger subject
than it might at first seem, and
Maienschein and MacCord take
fewer than 200 pages to anatomise
the complexities and ambiguities
that their simple question throws
up. It is to their credit that they
mostly focus on the big picture and
don’t make the biology any more
complex than it needs to be. ❚Simon Ings is a writer based in LondonIs the regeneration of a forest after
fire fundamentally the same as an
animal regrowing a body part? KA
RE
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