>>Art, havn't you heard of local mximum in a fitness field? Local minima can
>>be quite deep allowing a certain form to remain unchanged over long time
>>periods. Thus a bilaterian can remain basically the same (except for the
>>details) for a long time. And this is what we see in the lagerstatten.
Me:
>Indeed, and this appears to be the predominant manner in which
>evolution works itself out among the biosphere.
Glenn:
>But that doesn't mean that cell type number isn't thus increased.
Agreed. But I'm interested in the overall pattern in which we find
this localized increase. Remember that I asked why we haven't
seen an increase in things like porifera and arthropods. You
originally claimed that "if the arthropods and sponges had
increased their cell numbers then they would not be arthropods
or sponges." But hopefully now, after my reply, you can see
that this response is inadequate.
Glenn:
>>Once in a while a population breaks out of a local maximum and finds
>>another local maximum. And those that have moved on to other maximum are
>>now called by other names.
Me:
>Is there any experimental evidence to back this up? That is, I'd
>be interested in papers where the number of cell types has been
>*observed* to increase through evolution.
Glenn:
>What do you mean by observed?
Your explanation for cell types increasing here and not there
uses flashy words as if this is indeed the explanation. I'm just
trying to determine if there is actual substance behind the flash,
as the a priori and a posteriori approaches tend to blur in these
discussions.
>If you mean within the past 50 years? I
>would doubt it. But then you can't see a contininent move by watching it
>for a year. And you can't observe a glacier moving by watching it for 30
>seconds. Long term phenomenon require long-term observation. This idea
>that we must be there personally to observe something in order for it to be
>true is just silly. Were you there in Detroit when they made your
>automobile? How do you know it was made?
Couldn't you detect the movement of glaciers and continents with 50
years worth of measurements? In the case of increasing cell types,
we're not talking about finding an organism that has 0.00001 more
cell types. It should be easy to detect an increase from 16 to 17 cell
types with more than fifty years of observing mutants in nature,
and more importantly, artificially generated in the lab. Take the
homeotic mutants often brought out as an example of a mutation
capable of increasing complexity through changing the body plan.
We have seen MANY such mutations in flies and mice. Have any
ever increased the number of cell types?
Here's my point. You propose an explanation about populations
moving into different maximum fitness fields as (I suppose) the
mechanism behind generating more cell types. You write:
>If on the otherhand one can use observations of past events and
>gather data in that way, then yes the cellular type number has
>been observed.
What we observe is an increase in complexity among
a certain lineage in the fossil record. We can extrapolate and
argue indirectly this is a consequence of increasing cell type numbers.
But what we don't observe is this maximum fitness field explanation
as anything that it relevant to this localized trend. Thus, it may
*appear* as if you have offered a solid reply to Art's question,
but I don't think you have offered anything other than philosophy.
Glenn:
>>Thus evolution has increased the number of
>>cellular types by evolving worms into chordates, chordates into fish, fish
>>into amphibia, amphibia into reptiles and reptiles into mammals and birds.
Me:
>Yes, but keep in mind that only one lineage of fish gave rise to amphibians.
>The *vast* majority of fish evolution (ASAIK) doesn't entail this increase
>in cell types (the same point could be made for each step along your
>transitional series).
Glenn:
>So? I don't see what is such a big deal about that. Probabilistically it
>is unlikely that I will win the lottery and retire to Colorado. Yet one or
>two people will win the lottery. Maybe there is something special about
>their lineage. What do you suppose it is? Please tell me so I can win the
>lottery.
Let me try to explain. Yes, we seem to see an increase in complexity
*among vertebrates*, going from 64 to 210 cell types. Yet let's put
this indirect observation in its CONTEXT. Do we see similar increases
in other phyla or classes? No. In fact, even among the vertebrates,
we don't get increases apart from the
lamprey-fish-amphibian-reptile-bird/mammal
transition. And let's not forget bacteria, which constitute the majority of
the
biomass and have been evolving for over 3.5 billion years. Despite Matthew's
recent claim that, "Basically, when you start with something simple, there's
no
where else to go but towards complexity," bacteria have not (except,
supposedly,
for one single lineage) evolved towards increasing complexity. Thus, the
overall, general pattern of evolution has not been towards increasing
complexity
via increasing cell type numbers. This is the way evolution typically works.
And this would explain all the lab data which (AFAIK) has not detected
any new cell types as a consequence of the vast number of mutants that
have been analyzed. Yet it is within this overall context where we find this
exception of the lamprey-fish-amphibian-reptile-bird/mammal
transition. To me, this clearly suggests there is something special about
this transitional series.
Let's use your lottery example to demonstrate this. Say we institute a
national lottery. You win the lottery (lucky you!). Now, let's say the
lottery is played every week for every year until the year 3000. Since
the odds against winning are very low, there are only a total of 100
winners during this new millenium. Yet every one of those winners
is one of your descendents. How would you interpret this?
Glenn:
>>So, the answer to your question, like Mike's is that evolution has been
>>busy turning worms into men.
Me:
>Clearly suggesting there is something quite special about this transitional
>series given that evolution hasn't been nearly as busy anywhere else in
>life's history. In fact, I think I hear an echo of Van Till's "fully gifted"
>view here.
>I like Van Till's 'fully gifted creation'. That is close to what I
>believe. But that doesn't mean that God can't use chance to gift his
>creation to create us.
I'm glad we can end in agreement.
Mike