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Ch. 4: The Tree of Life 
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 Ch. 4: The Tree of Life
Ch. 4: The Tree of Life


Please use this thread to discuss the above listed chapter of "Darwin's Dangerous Idea: Evolution and the Meanings of Life" by Daniel Dennett.



Thu Feb 16, 2017 11:52 pm
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Post Re: Ch. 4: The Tree of Life
No special reaction here. I do feel like each chapter ends up being its own "rabbit hole" to a large extent. In this one we have the mildly interesting idea that many kinds of beginnings can only be recognized in hindsight. Hopefully he is going to use that for something, but would it have hurt him to say what?

Dennett doesn't take the question on in his discussion of "mitochondrial Eve", but it is worth noting that the last branching point to include all humans in its branches may have occurred before there were any humans, because we apparently have DNA fed in from the Neanderthals. This doesn't automatically mean that all humans are not on the same "human-only branch" but it could imply that there are "subsequently entangled" branches of humans which trace from a pre-human common ancestor by two (or more) parallel pathways, since interbreeding was evidently possible during part of the time with overlap between humans and Neanderthals (as asserted by "Clan of the Cave-Dwellers" before the DNA evidence was known).

Obviously this violates our intuition about speciation, but let's hope we are all going to have our understanding of speciation improved.



Fri Mar 17, 2017 10:52 am
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Post Re: Ch. 4: The Tree of Life
You hit the nail on the head, it was a mildly interesting discussion of speciation, I suppose it's necessary to get away from the essentialist notion of species. And then the whole Library of Babel idea. I think Dennett has used the book to go off on some semi-random digressions.

It may take me a while to get through, I put it down for a little bit



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Fri Mar 17, 2017 6:30 pm
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Post Re: Ch. 4: The Tree of Life
The library of Babel (or the library of Darwin) seems interesting enough for the first two or three pages, but after that, I kept waiting for a reason to be interested in it. Evidently Dennett worked under Quine, and is very interested in things like enumerating and classifying hypothetical things. Me, not so much.



Sat Mar 18, 2017 9:45 am
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Post Re: Ch. 4: The Tree of Life
Dennet's discussion of speciation reminds me of Dawkin's definition of a gene in The Selfish Gene. We tend to think of a gene for brown eyes and a gene for being tall, but of course in the real world these are bits of DNA with no definite starting place or ending place. There's no actual gene that for any specific trait—actually there might be some, but it's not usually so clear cut. So this is mostly a discussion of semantics. We think of species as having very clear lines of delineation, but it's muddy. Dennett says that speciation has a curious property: we don't know it's happening until we retroactively look back from a later point in time. I've heard that recessions are like that too.

I have also heard that there's no clear definition of life. We make arbitrary designations between "life" and a clump of organic matter, but there's no magic tipping point that allows us to distinguish one from another. In other words, it's complicated.

I'm taking my time reading this book. I read a lot of fiction and so I'm sort of switching back and forth. I hope Dennett gets into game theory at some point.


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Mon Mar 20, 2017 7:52 pm
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Post Re: Ch. 4: The Tree of Life
geo wrote:
We think of species as having very clear lines of delineation, but it's muddy. Dennett says that speciation has a curious property: we don't know it's happening until we retroactively look back from a later point in time.

Yes, I gather that there is a stage in which interbreeding is still possible, but becoming problematic.

It is interesting to think about why humans separated for many thousands of years, especially New World vs. Old World, did not become separate species. Evidently it takes longer than that, although clearly extinction can take less time than that.

geo wrote:
I've heard that recessions are like that too.
Yes and no. It's true that in real time it may take weeks before people's observation of falling sales is confirmed to be economy-wide and they realize it isn't just their business that is affected. But the bit about retrospective identification of recessions refers to a more dramatic issue, and one that does not really match up to the speciation case.

Recessions must be officially identified, because certain laws are triggered when there is a recession on. There are criteria identified by the NBER, which is charged with making the call, but none of them is hard and fast. In 2001, in particular, it was not clear that GDP was falling (before 9/11), which is normally a requirement, but GDP had slowed to barely perceptible growth and unemployment was rising, so the NBER declared (something like six months later) that the recession had begun. (Later data revisions showed GDP had in fact fallen).

It is quite possible that if there had been no 9/11, and the interference with air travel which followed, that the NBER would have read the tea leaves differently and claimed that no recession had happened. That was a hindsight classification, but in theory they are not supposed to base the call on later developments. Usually, of course, it is not such a close call.

When one asks if it is possible for the economy to linger at a tipping point, and have the possibility of going into a recession or not, 2001 is the classic case. But most recessions have reached the point of inevitability by the time the government is aware of them and ready to react. Maybe that is what your comment referred to, but I think that is a phenomenon of delay in receiving information rather than the need to watch dynamic factors play out a little before knowing whether the result is a turn up or down.



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Wed Mar 22, 2017 2:59 am
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