> These data seem to me (and to the authors of the study you quoted, and
> to other biologist I know) to fall quite short of being "paradigm-
> shifting" data, for the following reasons:
Thanks for the feedback. I understand your reasons. At least, this
will help to focus research interests!
> 1) It's not at all clear that molecular clock techniques are calibrated
> well enough to support the small error bars given by Wang et al. Their
> study is impressive, but molecular clock techniques extended over
> hundreds of millions of years are much better at giving relative dates
> than absolute ones. Their error bars take into account statistical
> errors, and perhaps some known systematic errors. However, there could
> well be (and probably are) some other, unaccounted, systematic errors,
> because obtaining absolute dates from such techniques relies on several
> assumptions which are accurate (in my opinion at least) to only about
> "plus or minus a factor of 2."
Having said this, the authors concerned have sought to address these
problems. If we go with your view, there is still an unresolved gap
in our knowledge.
> 2) I would not at all be surprised if many of the phyla split from each
> other several hundred million years before the Cambrian explosion, with
> their representatives being microscopic and soft-bodied -- living "in
> the shadow," as it were, of the Ediacaran critters.
The hunt for such tiny animals must already be on. Fossilised
embryos were found last year - if these can be found, there must be
potential for finding microscopic ancestors for the Cambrian fauna.
Until we do, there is a significant gap in our knowledge.
> 3) The paradigm of common ancestry is judged to derive strong support
> from the pattern of nested homologies which we see in gene sequences,
> genome organization, and developmental programs -- patterns well-
> matched to the fossil record. These patterns don't stop at the level
> of family, order, or class. They continue right up to the phylum
> level.
I think the Kuhnian revolution that I alluded to would result in a
rethink of these data.
> Recent developments in cosmology -- regarding the age of the universe -
> - offer an interesting story with many parallel features. (Did you
> happen to follow this story?)
Not closely enough perhaps. But I am aware of the problem you
describe.
> [some text snipped] But in the mid-
> 90's, as we got better measurements of Hubble's constant, the best
> estimates of the age of the universe kept creeping towards the lower
> end of that range, while the age of the oldest stars stubbornly stayed
> just as high or slightly higher than the best estimates of the age of
> the universe.
As I understand it, the most recent work on the Hubble Constant leads
to a 12 Ba cosmos. This is less than the ages of the oldest stars.
> Problem? Well, cosmologists weren't TOO worried about a
> "Kuhnian crisis." Why? First, comfort was taken in the fact that
> these two independent techniques gave numbers which really were pretty
> close to each other. Second, each technique relied upon several
> assumptions which could -- upon better examination -- potentially shift
> their predictions by perhaps 10 or 20 percent. And that is exactly
> what happened in the last few years!
As indicated above, the problem seems to be acute still.
> As it turns out, one big
> assumption in previous estimates of the age of the universe was that
> the "cosmological constant" was exactly zero. But in the last few
> years, astronomers have found pretty good evidence that the
> cosmological constant is not zero. If we plug the new non-zero value
> for the cosmological constant into the equations for the age of the
> universe, and the age of the universe is once again comfortably longer
> than the age of the oldest stars. Crisis resolved (for now).
But the Cosmological Constant is a "fudge factor". It is there just
to make the equations coherent. It represents another gap in our
knowledge - until there is a foundation for this constant in physics,
the resolution of the crisis is little more than covering over the
cracks with wallpaper.
> This story which played out so recently in cosmology looks -- to me --
> just like what's happening right now regarding the different techniques
> (geological and molecular) for dating the origin of phyla.
Just what I was thinking!
Best regards,
David J. Tyler.