Jim Bell first proposed that the rapid appearance human culture was
evidence -- similar to the rapid appearance of first life and the rapid
appearance of phylla in the Cambrian era -- for God's intervention in
history. (At least, that's how I interpretted his post.) Jim Foley
replied -- correctly, I believe -- that anatomically modern human fossils
date back at least a hundred thousand years before the appearance of the
Cro-Magnon culture (dated about 40,000 years ago). Therefore, the
appearance of human culture is not a biological-evolution issue, but
rather is analogous to other rapid cultural changes (e.g. the Industrial
Revoltuion). The rapid appearance of human culture MAY have been due to
God's intervention, but since the activity of intelligent humans is also
involved, it would be as difficult to argue this _scientifically._ (Just
as it would be difficult to scientifically prove that the industrial
revolution was divinely orchestrated.)
Jim Bell then raised the biological/evolutionary issue of the "rapid"
appearance h.sapiens. That is where the debate is now.
-------
Jim Bell writes:
JB> The "explosion" I'm talking about is sudden apperance on the scene of a
> creature that cannot be explained by any natural means. As Goodman
> notes: "Modern man is an extraordinary phenomenon, a complex system
> of distinctive physical and mental traits, a whole considerably
> greater than the sum of its parts. Physcially and mentally he took a
> great leap beyond his predecessors, a leap which cannot be explained
> by the demands of the environment or random mutation."
Jim, I think you invite frustrating debates about "proving a negative"
when you use phrases like "cannot be explained by any natural means" or
"cannot be explained by ... environment or random mutation." You might
consider prefacing those phrases with, "In my opinion...." or "In
Goodman's opinion...." Simply asserting the point under contention is
seldom a successful debate style.
It is fair and proper to say that attempted naturalistic explanations are
still very sketchy. You do well when you cite sound objections to those
attempted naturalistic explanations. But phrases like "cannot be
explained..." (especially given science's track record for explaining the
unexplainable, and given the fact that many scientists DO disagree with
you) tend to shift the focus away from the evidence and create
meta-arguments.
Regarding the biological evidence, Stephen Jones wrote:
SJ> "If one attempts to read the complexities of the story, one is not
> surprised that man is alone on the planet. Rather, one is amazed and
> humbled that man was achieved at all. For four things had to happen,
> and if they had not happened simultaneously, or at least kept pace
> with each other, the bones of man would lie abortive and forgotten
> in the sandstones of the past:
>
> 1. His brain had almost to treble in size. 2. This had to be
> effected, not in the womb, but rapidly, after birth. 3. Childhood had
> to be lengthened to allow this brain, divested of most of its precise
> instinctive responses, to receive, store, and learn to utilize what it
> received from others. 4. The family bonds had to survive seasonal
> mating and become permanent, if this odd new creature was to be
> prepared for his adult role.
>
> Each one of these major points demanded a multitude of minor
> biological adjustments, yet all of this-change of growth rate,
> lengthened age, increased blood supply to the head, moved apparently
> with rapidity. It is a dizzying spectacle with which we have nothing
> to compare. The event is complex, it is many-sided, and what touched
> it off is hidden under the leaf mold of forgotten centuries.
> Somewhere in the glacial mists that shroud the past, Nature found a
> way of speeding the proliferation of brain cells and did it by the
> ruthless elimination of everything not needed to that end. We lost
> our hairy covering, our jaws and teeth were reduced in size, our sex
> life was postponed, our infancy became among the most helpless of any
> of the animals because everything had to wait upon the development of
> that fast- growing mushroom which had sprung up in our heads."
> (Eiseley L., "The Immense Journey", Victor Gollancz: London, 1958
> p122-123)
>
> I would like to see all that plausibly explained using purely natural
> causes! :-)
So would I. I've seen a few hints, which I'll talk about later in this
letter....
Bill Hamilton replied to Stephen,
BH> But perhaps it's useful to remark on what we mean by
> "explanation". Typically, scientific explanations explain the mechanisms
> that contribute to an observed phenomena. IOW they explain natural effects
> in terms of natural causes. It is a mistake (and people on both sides of
> the origins debate make this mistake) to assume that a scientific
> explanation explains ultimate causation. It doesn't. The kind of
> explanation Stephen is asking for is an explanation which gets at
> fundamental causes -- something totally outside the capability of empirical
> science. [...]
>
> Scientific explanations aim to determine what methods the designer used.
> Theistic explanations aim to understand (to the extent He allows it) the
> Designer.
I agree with the last paragraph completely, and I agree that it is a
mistake to assume that a scientific explanation explains ultimate
causation. (To use Howard VanTill's terms, "governance" means more than
"behavior," and "origins" means more than "formative history.")
However, I interpretted Stephen's remarks as questioning the _method_ of
human formative history, not the ultimate causation. We should try to
find some methodological answers to Eiseley's points. (Does anyone know
any good books on the subject? Anything in the talk.origins FAQ?)
------------
Jim Bell contributed:
JB> "Mitochondrial Eve" studies are talking about the appearance of modern man.
> Davis and Kenyon state: "If the theory turns out to be confirmed in some
> reasonable approximation of its current form, it would have three major
> implications in man's quest for his ancestry: 1. It woud mean that humanity,
> as represented by its contemporary peoples, is dramatically younger than
> traditionally conceived by most scientists.
How do Davis and Kenyon define their terms? If Davis and Kenyon mean that
"all contemporary peoples share a more recent common ancestor than
traditionally conceived by most scientists," they are correct. If Davis
and Kenyon mean that "modern h.sapiens as a species is younger than
traditionlly conceived by most scientists," then I belive they are
incorrect. A reproductive bottleneck doth not a new species make. AFAIK,
"modern" human fossils predate the supposed time of "Mitochondrial Eve."
JB> [if "Mitochondrial Eve" is correct] 2. It would eliminate Neanderthal
> as a candidate for ancestry to European peoples.
Yes, I believe that follows.
JB> 3. It would eliminate the
> vast majority of Homo erectus populations across Europe and Asia as ancestral
> to man..."
I'm not sure about that. A reproductive bottleneck fans out on both the
ancestral and the progeny sides. Why would those H.erectus be eliminated
as ancestral?
---------------------
Stephen Jones again:
SH> Specifically, what plausible natural causes
> of mutation + natural selection led to all the following happening:
>
> 1. "change of growth rate";
> 2. "lengthened age";
> 3. "increased blood supply to the head"
> 4. "proliferation of brain cells"
> 5. "lost...hairy covering"
> 6. "jaws and teeth were reduced in size"
> 7. "sex life...postponed"
> 8. "infancy became among the most helpless of any of the animals"
> 9. "the development of that fast- growing mushroom which had sprung up
> in our heads."
> 10. "Each one of these major points demanded a multitude of minor
> biological adjustments;
>
> Even if each one of these events could be described in terms of
> purely natural causes, the problem is:
>
> 1. what were those purely natural causes?
> 2. what caused them all to happen: a) at about the same time; b) in
> the right sequence?
> 3. what is the likelihood of them all happening: a) at about the same
> time; b) in the right sequence?
>
> Even "intelligent guesses" would do for starters! :-)
That's fair. Eiseley's points require good answers. As you know,
developmental biology is just begining to get onto its empirical feet, so
empirical answers (either in favor of, or opposed to, naturalistic
explanations) won't be available for a few years or decades. As for
intelligent guesses, I'll do my best. Since I just switched from physics
to electrophysiology, my grasp of the more relevant disciplines
(developmental, molecular, and evolutionary biology) is still pretty slim.
But I've encountered a few, what I would call, "hints."
Let's start with the problem numero uno: the rapid increase in brain
size. About a year ago I attended a seminar which attempted to answer
some questions about brain development in mammals. The questions can be
summarized by this example: why is it that in two related species of
squirrel, a species which has twice as much brain for auditory processing
will also have TEN times as much cerebral cortex? The researchers
measured the average mass of 14 different brain regions for about a dozen
species of mammals, from rats to humans. The results were plotted x-y-z:
the x-axis had the animals ranged according to total brain size; the
y-axis had the brain regions arranged according to the amount of time
between conception and when the cells of the particular region matured.
The z-axis was the mass of each brain region. The result was that the
brain region mass was nice, smooth power-function of both variables. Each
species had different ratios of brain mass for the different brain regions
(smaller-brained animals had proportionally more of the "primitive" areas
of the brain and proportionally less cerebral cortex). But as the brain
size increased from species to species, the SAME power-law fit the ratios
of the _14_ different brain regions.
Based upon that result, I would offer an "intelligent guess" that there is
a highly similar developmental program for all mammalian brains, and that
fairly simple mutations in the timing of that program can lead to large
changes in brain mass, and particularly in the size of the cerebral
cortex.
A lot of developmental neurobio papers I've seen lately suggest that
mitotic cells are heavily dependent upon target-derived extra-cellular
signals (chemical messengers) to determine how they mature and specialize.
These discoveries, combined with the sometimes surprisingly normal
development of many "mutant" and "knockout" mice, leads me to speculate
that many -- though not all -- of the "minor biological adjustments"
required for a larger brain (more glial cells, larger skull, more blood
vessels) come along "for free" with a bigger brain.
Just to show you that I have limits to my speculation, I'm not going to
offer a guess how the slowing of human physical development (helpless
infancy, longer childhood, etc.) came about simultaneously with increased
time devoted to brain development.
As for hair, well, did you hear about the "werewolf" gene reported in
_Science_ (or was it Nature?) a few months ago? :-)
In a recent post, someone (I forget who) dropped the term "autocatalytic"
to describe the increase in human brain size. That term is worth a little
extra explanation and consideration. The idea, as I understand it, is
that a certain biological feature, through sexual selection and/or
reproductive success, catalyzes its OWN continued change. The example
given in _The_Blind_Watchmaker_ is of very long tailfeathers in the males
of a certain bird species. If the same set of genes are responsible not
only for giving a male longer-than-average tailfeathers, but also for
causing a female to PREFER males with longer-than-average tailfeathers,
then in each genereation the feature is reinforced, leading (in theory) to
a geometric increase in tail feather size each generation until a
stabilizing factor (e.g. ease of capture by predators) is reached.
Presumably, autocatalyzing features are an evolutionary rarity, but when
they do occur, they promote much faster-than-normal change. I think it is
a pretty good "intelligent guess" that, at some point, brain size in
hominids became autocatalyzing.
Well, Stephen, I doubt if I convinced you that we will someday explain, in
terms of natural mechanisms, the tripling of hominid brain size in a few
millions years. However, I hope I _did_ convince you that I've seen
enough hints to keep looking for naturalistic explanations, and that it is
not unreasonable for me to expect eventual success. I can't offer any
more facts or guesses without stopping my real work and launching a
literature search, but I'll keep my eyes and ears open.
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"Danger: Sharp learning curve ahead." | Loren Haarsma
(_Dilbert_) | lhaarsma@opal.tufts.edu