
The ancestors are not among us - Hooke
http://for-the-love-of-trees.blogspot.com/2016/09/the-ancestors-are-not-among-us.html
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trjordan
OK, I get the argument.

But is there no validity to the idea that a species has not meaningfully
changed in many years? I've heard this idea that modern sharks are closer (in
physiology) than human to our common ancestor. If I want to think about the
common ancestor, I should think about a shark, not a human. I get that modern
sharks are different than ancient sharks, but doesn't the idea of "living
fossil" help me understand how much another species has changed over some time
period?

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thaumasiotes
> doesn't the idea of "living fossil" help me understand how much another
> species has changed over some time period?

No, it doesn't.

First, you'd need a measurement of "change". Without that, the question "how
much change has occurred?" is, obviously, totally meaningless.

Once you supply a measurement of "change", you'll notice one of two things:

(1) (if your definition was motivated by defending the concept of living
fossils): You've hung on to the idea that "living fossils" have changed less
than "modern species", but your definition of "change" serves no useful
purposes.

(2) (if your definition was motivated without reference to "living fossils"):
"Living fossils" mysteriously seem to be no different than any other species.

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nerdponx
This is a bizarre argument to me. Economists, for instance, do not have an
agreed-upon definition for the "money supply". Nevertheless, it is perfectly
reasonable to operate as if such a definition existed, so long as the details
of its definition or not important in the discussion.

Similarly, this is in the same vein as writing pseudocode containing a
function that has not yet been defined. The exact execution steps of the
program are not defined, but you can still reason about its flow all the same.

To say that we cann't determine whether a species has changed, because we
don't have a meaningful way to measure species change, is fine. It does not
follow, however, that species change is inherently unmeasurable, and that
therefore we just can't talk about it at all.

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thaumasiotes
> It does not follow, however, that species change is inherently unmeasurable,
> and that therefore we just can't talk about it at all.

Sure, and I didn't say or imply that anywhere. I said that no matter how you
conceptualize evolutionary change, the concept "living fossil" will be
nonsense.

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kazinator
> _I think this use of the term is related to the misconception that some
> living taxa are the ancestors of other living taxa._

The misconception is that some living taxa _are identical_ to some ancestral
taxa from which something else has also descended that is different.

But isn't it the case that some are at least close (for some intents and
purposes)? Crudely, apes haven't gone away because there are humans. Bacteria
are still here and so on. Just they are not exactly the same like bacteria 300
million years ago.

~~~
nathandaly
I think this is exactly the distinction the article is trykng to make. The
statement "apes haven't gone away because there are humans" has a false
premise: apes have changed a whole bunch since the common ancestor they share
with humans, just like humans have. Back when there were no humans as we know
them, there were also no apes as we know them.

As far as I remember from biology, even if there is no selection pressure on a
population, the population will still experience genetic drift and will still
change over time.

