Posted by: Rob Viens | July 23, 2013

Three Blind “Mice” and Jean-Baptiste Lamarck

After getting thrown off course by “mysterious” currents for a day or so, the Beagle returned to Maldonado for one last chance to finish preparing for the trip south. Darwin writes:

“Gained the harbor of Maldonado. — the weather being very light & hazy detained us. — We had a strong instance of the dangerous navigation of the Plata; having good Latitude observations & having only left port for two days we were nearly 40 miles out of our reckoning. This was entirely owing to a strong current. — of which there was no means of previously ascertaining the existence.” (July 21/22)

Along with the brown rat discussed in the last post, Darwin also talks about another rodent in his Zoological Notebook – the tuco-tuco.  Last Fall he discovered some fossil tuco-tuco teeth, so I’ve already written a little about this unique little critter (see Tiny Tuco-Tuco Teeth).  But I thought it might be an interesting time to share Darwin’s comments amount Lamarck in regards to the blind tuco-tuco Darwin discovered in Uruguay recently.  Let’s just say, the Beagle may have been lost at sea for a day, and the tuco-tuco’s may have been blind, but in Darwin’s mind it was Jean-Baptiste Lamarck who was more in the dark than anyone (or anything) else.

First a note on the tuco-tuco that inspired the conversation:

“The man who caught them asserted that very many are invariably found blind. A specimen which I preserved in spirits was in this state; Mr. Reid considers it to be the effect of inflammation in the nictitating membrane. When the animal was alive I placed my finger within half an inch of its head, and not the slightest notice was taken: it made its way, however, about the room nearly as well as the others. Considering the strictly subterranean habits of the tucutuco, the blindness, though so common, cannot be a very serious evil; yet it appears strange that any animal should possess an organ frequently subject to be injured.” (Voyage of the Beagle)

Brazilian tuco-tuco – Ctenomys brasiliensis (from Alcide Dessalines d’Orbigny, 1847)

tuco tuco

Read that last sentence again – Darwin is teasing his reader about the significance of an observation that would later be quite relevant to the concept of evolution by natural selection.  Remember that this particular quote was written after he returned to London, at a time when many scholars suggest that Darwin already had a basic idea of his evolutionary hypothesis.  It makes one wonder what he already had figured out when he wrote this line in Voyage – just why does that little tuco-tuco have an eye at all when it is ultimately a disadvantage?

In any case, the best part of the paragraph comes next when Darwin takes the opportunity to call out one of his contemporary (sort of) rivals in evolutionary thought. He comments on how Jean-Baptiste Lamarck would react to this blindness – taking the opportunity to get in a little “dig”:

“Lamarck would have been delighted with this fact, had he known it, when speculating (probably with more truth than usual with him) on the gradually-acquired blindness of the Aspalax, a Gnawer living under ground, and of the Proteus, a reptile living in dark caverns filled with water; in both of which animals the eye is in an almost rudimentary state, and is covered by a tendinous membrane and skin. In the common mole the eye is extraordinarily small but perfect, though many anatomists doubt whether it is connected with the true optic nerve; its vision must certainly be imperfect, though probably useful to the animal when it leaves its burrow. In the tucutuco, which I believe never comes to the surface of the ground, the eye is rather larger, but often rendered blind and useless, though without apparently causing any inconvenience to the animal: no doubt Lamarck would have said that the tucutuco is now passing into the state of the Aspalax and Proteus.” (Voyage of the Beagle)

Jean-Baptiste Lamarck has the distinction of being the scientist who most intro biology students think of as being the guy who got evolution wrong.  And clearly, in writing less than a decade after his death, Darwin’s quote suggests that he did not think too highly of his ideas either. But in reality, Lamarck gets a bad rap. He was a good scientist, a leader in his field and strong proponent for the idea of evolution. It just so happens he got the mechanism wrong.

Jean-Baptiste Lamarck:

Jean Baptiste Lamarck

Lamarck was born in France in 1744 (making him 65 by the time Darwin was even born) and died in 1829 (just 2 years before Darwin’s departure on the Beagle). After serving in the army, Lamarck returned to the world of science, concentrating his efforts on his interest in botany.  After publishing some notable books on the plants of France, he began to turn his attention to animals – starting (like Darwin) with an interest in invertebrates. (He published a landmark 7-volume publication on them in 1801.) By the time the Muséum national d’Histoire naturelle opened in 1793, he was the logical choice to be appointed the professor of zoology.

Ultimately, however, Lamarck his best known for his contributions to evolution.  He was certainly one of the scientists that helped pave the way for Darwin’s hypotheses – making a convincing argument that plants and animals changed/evolved over time. In fact, blind moles were one of the animals he used as evidence for his hypotheses. But he was also convinced that there was a law of nature that said that living things were progress “up a ladder” towards greater complexity. (Of course this is not the case, we now know that living things can just as easily evolve a less complex structure if it gives them an advantage.)  He also suggest that living things adapted to their environment by “working out” organs or body parts.  The classic example was the suggestion that a giraffe’s neck grew longer because the giraffe stretched it out to reach the leaves on the tall trees (i.e., a regular neck-lengthening routine). Furthermore he suggested that these acquired traits could be passed on to offspring – what is often called “inheritance of acquired traits”.  In other words, if you worked out, your kids would have big muscles, too. And if they worked out and their kids worked out, and so on…you could evolve a race of super-muscular humans.  Alas it does not work that way (which is probably a good thing for us). We now work under the hypothesis that what we do to our bodies and what we pass on through our genes are two different things (for the most part).

I do think Darwin came to respect Lamarck’s contributions to the field of evolution (even if he did not agree with the details), but as a young man still making his name in the sciences, he couldn’t help but poke at the ideas of a rival.

Did Lamarck get some things wrong? Yup.  Is that bad?  Well good or bad, it is a natural part of the progression of science. Darwin got things wrong too, though he ended up getting some big ideas right, too. But that is how we learn aout the world around us.

And here is the “kicker”  – there are some things about the inheritance of acquired characteristics that may be turning out to be correct after all.  The growing field of epigenetics is revealing that our environment may impact gene expression in such a away that these characteristics are passed on to our children. In other words, a characteristic that I “acquire” by being exposed to a chemical (let’s say tobacco smoke) could be passed on and exhibited by my offspring.  Not bad JB – turns out you may have been on to something! (RJV)

Advertisements

Responses

  1. Great entry!

    • Thanks Jim! And thank you for all your support and encouragement over the first couple years of the voyage – it helps keep me inspired to keep going!


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: