Current Biology Vol 17 No 10
eggs unlike their own? One
possibility is that they are new
hosts, with insufficient time
to have evolved defences.
The other is that defences are
costly — for example, egg
rejection may involve recognition
errors — and parasitism levels
may be below the threshold
where it pays to sustain these
costs. Even among host species
that have evolved egg rejection,
individuals are less likely to
reject eggs when cuckoos are
locally scarce. Cuckoo tricks will
also reflect a trade-off between
costs and benefits. A cuckoo
nestling that kills host young
rids itself of competition once
food arrives but, without the
assistance of other nestlings, it
now has to work harder to solicit
provisioning. This involves some
remarkable tricks; common
cuckoos have rapid begging
calls that sound like many host
young, and Horsfield’s hawk-
cuckoos have wing patches that
simulate extra gaping mouths.
Nevertheless, hosts sometimes
reject cuckoo chicks. Why is this
not more frequent, especially
in cases where the cuckoo is
so different in appearance from
the host’s own young? Further
molecular genetic analyses will
enable us to calibrate when
cuckoos and their host- races
evolved from a common
ancestor and to resolve the
time course of these marvellous
Where can I find out more
Davies, N.B. (2000). Cuckoos, Cowbirds
and Other Cheats. (London: T. and A.D.
Kilner, R.M. (2005). The evolution of
virulence in brood parasites. Ornithol.
Sci. 4, 55–64.
Lahti, D.C. (2005). Evolution of bird eggs in
the absence of cuckoo parasitism. Proc.
Nat. Acad. Sci. USA 102, 18057–18062.
Langmore, N.E., Hunt, S. and Kilner, R.M.
(2003). Escalation of a coevolutionary
arms race through host rejection of
brood parasitic young. Nature 422,
Payne, R.B. (2005). The Cuckoos. (Oxford:
Oxford University Press).
Rothstein, S.I. and Robinson, S.K. (1998).
Parasitic Birds and Their Hosts.
Studies in Coevolution. (Oxford: Oxford
Department of Zoology, University
of Cambridge, Downing Street,
Cambridge CB2 3EJ, UK.
Stephen Potter’s Lifesmanship.
Having spied the master during
the first half of a concert, the
neophyte approached him later at
the pub, and challenged as follows:
“The Debussy (in the second half)
was not good, don’t you think?”
To which the master replied with
astonishment: “You mean you
stayed for the Debussy?”
I wish people wouldn’t worry
about being too transparent. I
once asked Francis Crick why
he spent the day with a pile of
Scientific American magazines and
he said “When you are learning
something new the hardest thing
is to get the basic idea.” The truth
is, most of the time I’d prefer to
hear what the speaker thinks than
what he can prove — the proof
can come later. I’ve never attended
a seminar in which there were
too few slides, or the slides were
too simple, or the speaker failed
to use enough technical terms,
or — amazingly — spoke for too
brief a time. Aaron Novick told
me, long ago, that I had to go to
meetings and seminars — only by
looking at the speaker, he said,
would I know who was believable.
That was back in the days when
there was only a handful of
potentially interesting people.
Let me put the matter this
way. I recently heard a seminar I
loved. The young woman sailed
along briskly, every sentence
having a point without being
pedantic — there was a salient
quality of mind. I was reminded: a
seminar is a performance that has
to be rehearsed (even if silently,
in bits) over an extended period.
It is not just a matter of choosing
which words to use — equally
important is the choice of which
words not to use. In an otherwise
good talk, speaking a wrong word
or phrase can be a disaster — you
or the audience will be diverted
into explanations (or puzzlements)
you desperately want to avoid.
Clear thinking does not guarantee
a good talk: Matt Meselson told
me about a well-known scientist
who, giving a seminar, gave the
impression that a recording of a
perfectly coherent talk was being
played in his head, and he was
commenting on it as it went by.
Unfortunately the way ‘it used
to be done’ is not necessarily a
A visitor, giving a seminar at Cal
Tech, found to his amazement
that when he had finished his
introduction Max Delbrück raised
his hand and said “Stop! Say
it again.” “Say what again?”
asked the speaker, and Max said
“Everything you just said.” So he
repeated, word for word, his 15
minute introduction at which point
Max raised his hand, said “Stop.
That’s what I thought you said,”
and walked out.
What prompted Max — who
imposed his formidable will and
intellect on the nascent field of
molecular biology — to walk out?
My guess is that the lecturer didn’t
say anything wrong so much as
he didn’t say anything at all — at
least not clearly. I go to seminars
surreptitiously, if possible, and
only if there is an inconspicuous
escape route. The danger is
that the speaker will begin by
bandying about some key terms,
showing a few bewildering slides,
and referring to all this stuff we
supposedly already know. I find
myself struck by a sentence,
wondering what exactly was
meant; what constructs is this
person carrying around in his
head? And by the time I emerge
from my musings the seminar is
half over, all is lost, and I sheepishly
extricate myself. This is risky — I
have to rely on friends who can sit
in the fog to extract whatever of
importance might be there.
Concerts too — I try to sit at
the end of rows to facilitate early
getaways when required; I can
always puzzle over the review
the next day. In ‘Old Vienna’, so
the story goes, there was a cost
for such anti- social behavior:
entrance to concerts was free
but there was a charge if you left
early. I am reminded, in a further
digression, of a lesson taught
by the master to the neophyte in