I wrote to Carl Zimmer, and he replied within two hours. That's pretty cool!
So I thought I'd put everything I learned about this here as an answer with all the links, and if you guys have more to add, feel free to post more answers.
My Original Email:
Currently I'm reading She Has Her Mother's Laugh, which is a fascinating book, and I'm thoroughly hooked. However, while reading it, I came across this passage that troubled me. The bit in question is in Chapter 2: Traveling Across the Face of Time.
"It also meant that the inheritance of acquired traits - taken as a
fact by Hippocrates, Lamarck, and Darwin alike - was impossible."
From what I've read on the subject over the years, almost unanimously people agree that Darwin opposed the idea of Lamarckian heredity. I thought that Darwin's idea is that small modifications arising from random mutations (although he didn't know about DNA and genes at the time), if beneficial, were retained and accumulated over the generations resulting in new species. But is it not the case? Did actually Darwin subscribe to the idea of Lamarckian heredity?
I did a little bit of research on this, and found some conflicting and confusing information.
To start with, I've read Darwin's Origin of Species and though I remembered him opposing the idea, so I searched through the book again and found the following para.
Thus, as I believe, the wonderful fact of two distinctly defined
castes of sterile workers existing in the same nest, both widely
different from each other and from their parents, has originated. We
can see how useful their production may have been to a social
community of insects, on the same principle that the division of
labour is useful to civilised man. As ants work by inherited instincts
and by inherited tools or weapons, and not by acquired knowledge and
manufactured instruments, a perfect division of labour could be
effected with them only by the workers being sterile; for had they
been fertile, they would have intercrossed, and their instincts and
structure would have become blended. And nature has, as I believe,
effected this admirable division of labour in the communities of ants,
by the means of natural selection. But I am bound to confess, that,
with all my faith in this principle, I should never have anticipated
that natural selection could have been efficient in so high a degree,
had not the case of these neuter insects convinced me of the fact. I
have, therefore, discussed this case, at some little but wholly
insufficient length, in order to show the power of natural selection,
and likewise because this is by far the most serious special
difficulty, which my theory has encountered. The case, also, is very
interesting, as it proves that with animals, as with plants, any
amount of modification in structure can be effected by the
accumulation of numerous, slight, and as we must call them accidental,
variations, which are in any manner profitable, without exercise or
habit having come into play. For no amount of exercise, or habit, or
volition, in the utterly sterile members of a community could possibly
have affected the structure or instincts of the fertile members, which
alone leave descendants. I am surprised that no one has advanced this
demonstrative case of neuter insects, against the well-known doctrine
If you read the last few sentences, Darwin says "accumulation of numerous, slight, and as we must call them accidental, variations,..." which to me indicates he's referring to random mutations in genes even though he didn't know what genes were. Furthermore, a little later, "For no amount of exercise, or habit, or volition, in the utterly sterile members of a community could possibly have affected the structure or instincts of the fertile members, which alone leave descendants." and "I am surprised that no one has advanced this demonstrative case of neuter insects, against the well-known doctrine of Lamarck."
To me this clearly indicates he was opposed to the idea of Lamarckian heredity. Could you please explain a little bit more about your stance? I'd love to hear the different viewpoint and the reason(s) behind it.
Since I was curious about this, I posted the same question on StackExchange biology forum.
One of the users pointed me to an article by Michael T. Ghiselin who seems to be in agreement with you regarding the matter.
While some of his points about textbook authors misunderstanding Lamarckian heredity sounds fair and valid, I can't quite see how he came to the conclusion that Darwin agreed with Lamarck. The passage he points to (Lamarck was the first man whose conclusions ...") doesn't say anything about Darwin agreeing with Lamarck about acquired traits being passed down the generations.
In Wiki page about Pangenesis, the following is mentioned just as you have in your book.
"Darwin thought that environmental effects that caused altered
characteristics would lead to altered gemmules for the affected body
part. The altered gemmules would then have a chance of being
transferred to offspring, since they were assumed to be produced
throughout an organisms life.2 Thus, pangenesis theory allowed for
the Lamarckian idea of transmission of characteristics acquired
through use and disuse. Accidental gemmule development in incorrect
parts of the body could explain deformations and the 'monstrosities'
Darwin cited in Variation."
Which indeed supports your viewpoint, but to me that seems like a direct contradiction to Darwin's own words in Origin of Species.
So which of it is true? Or, since Pangenesis theory came after he published Origin, did he change his mind later?
Carl Zimmer's reply:
Thanks for your email. I've also had to struggle to work out Darwin's
views about Lamarck--they were complicated and changed over his
career. Basically, the more Darwin thought about heredity, the more he
warmed up to the possibility of the inheritance of acquired
characters. I've attached a few good papers that may be of interest.
Best wishes, Carl Zimmer
Papers Referred by Carl Zimmer:
Gemmules and Elements: On Darwin’s and Mendel’s Concepts and Methods in Heredity.
Lamarck, Evolution, and the Inheritance of Acquired Characters.
orgThe Early History of the Idea of the Inheritance of Acquired Characters and of Pangenesis.
I haven't read those papers yet, will do so when I find time and hopefully it will shed some more light on it.
So, I'm still not quite sure about the issue, but I do think Carl Zimmer's point of view is fair enough, that it is possible Darwin's views evolved over time. Particularly, given that nobody knew what exactly even heredity means at the time, it's possible that Darwin thought it cannot just be ruled out. Besides doesn't seem like he was out campaigning for the idea, rather allowed for it with his Pangenesis hypothesis.
After all, Darwin's theory was about how small modifications accumulated over time leads to species change, not how those changes occurred in the first place. So, while it turned out to be untrue, if there was a mechanism in which experiences could be stored in the unit that transmitted heredity, you can probably incorporate that into Darwin's theory of evolution. That probably was a line of thought Darwin had.