Natural Science Forum / Biology / Paleontology / January 2007

    For the benefit of the ignorant (that's me) could you briefly outline
some others?
    I'm more aware of the obvious clinical manifestations (such as
development of bacterial resistance to antibiotics).
    Others?

Steve

***What does it mean to have a "numerically consistent model of
evolution
that is supported by fossil evidence"? As far as I can tell, the fossil
record does not strongly constrain evolutionary models, and thus can't
be said to support one or another, nor can it be said to be
inconsistent
with any of them.***

It means roughly what it says.  Specifically, try to get the fossil
record -- with or without allowing for extinction events to match a
model of simple exponential growth in number of taxa.  The equation for
exponential growth is pretty simple N = R ^ T where N is the number of
anything.  R is the growth rate (well OK, for the literal minded, it's
really 1 + the growth rate i.e a growth rate of 1% per unit time would
be experessed as 1.01).  T is time.  One equation in two unknowns.
Given two data points, it should be possible to determine the rate at
which new new taxa are being created.  So pick a value for the Lower
Cambrian -- say 500 taxa (which seems low) and a value for today say
5,000,000 taxa.  That implies a growth rate of about 1.0000000176.
Which says that the number of taxa doubles roughly roughly every 5.68
million years.  So when was there only one taxon? I make it somewhere
before 1000ma.

The fossil record OTOH would seem to indicate that metazoans appeared
later and diversified much more rapidly than that.  You can try
juggling the numbers, allowing for extinction events, etc.  My very
cursory efforts lead me to believe that any model that matches the
fossil record is way too contrived to be credible.  Neither do I think
(could be wrong) that magic with fractal distributions, etc is going to
create a model that looks all that much better.

I'm sure that I'm not the only person to try this approach.  If the
numbers actually could be made to work plausibly, I think a numerical
model of evolution would be a standard element of paleontology.

So, I think that, The problem isn't that evolution isn't constrained.
It's that we don't understand the constraint.

===

I agree that number of genera is a sloppy metric, but I submit that it
is better than number of species.  At least genera usually differ in
some meaningful way -- which tends not to be as true of "species".  And
I'm skeptical that this is a problem where cladistics can help although
maybe a decent mathematician (which I certainly am not) can come up
with a tool.  In any case, cladistics clearly has some troubles when
the relationships between taxa are a (near) total mystery as tends to
be increasingly the case in the Atdbanian and before.  Even if we don't
understand the relationships, we can still make possibly useful counts
of how many distinct kinds of critters appear to have existed..

===

***Not actually clear, the fossil record being fragmentary and all. The
oldest diverse Cambrian fauna are around 530-520 million years old,
e.g.
the Chengjiang. But we depend on rare lagerstatten for this
information.
It's not clear how short the time period was -- and it depends also on
what you want to count. Remember that a majority of animal phyla have
no
pre-Quaternary fossil record.***

The Maotsianshan Shale gets a lot of publicity because there are so
many taxa and they are so well preserved.  But there are many other
Early Cambrian and older sites -- with more being found every year.
With a few exceptions like the presence of vertebrates, I don't think
our view of the Early Cambrian would be greatly different without the
Chengjiang fauna.  Also, I personally think that the rules of fossil
preservation probably changed significantly around 550 million years
ago with the advent of active sediment feeders and the destruction of
widespread microbial mats.  My guess is that Ediacaran fossils will
probably prove eventually to be substantially more common than we think
now.  But they will be faint, difficult to interpret, and largely
lacking in complex features that help in differentiation of taxa.
There are organic looking structures on bedding planes in the less
altered exposures of my local Ediacaran formation, but I'll be damned
if I can tell you what kind of plants or animals they might represent.

***This is nonsense. Almost every modern evolutionist believes that the
mechanism behind adaptive evolution (there are other kinds, but that's
what you probably mean) is natural selection acting on random mutation.
And the random mutations in question are generally small changes of the
sort Darwin was speaking of. Where have you been for the past century?
***

John, the proper order is Ready, Aim, Fire.  Not Ready, Fire, Aim.
What I said was that Darwin was wrong about how changes occur -- which
he was.  I did not say that Evolution en toto had been disproved.  Nor
do I think that.

As for mutations being small steps.  Not really that clear.  Most
aren't visible at all.  (And, for that matter, most surely are lethal).
But the mutation mechanism permits much larger changes than gradual
change.  If anything, this supports evolution as it allows for large
enough changes to matter.  Not that big a deal nowdays I think, but
maybe important in the Ediacaran and Lower Cambrian when there seems to
have been quite remarkable (by modern standards) diversification in a
relatively short time span.

***I'm not sure they're at all relevant to the OP's post. ***

Nor, in retrospect, am I.