On Mon, 29 Jul 1996 2:26:55 -0500 (CDT), NIIIIIIICHOLAS MATZKE wrote:
[continued]
NM>For some reason (in the case of monotremes, geograpic isolation
>and lack of competition) they retain some of the traits that were
>lost in the now-common group (placentals).
There is no palaeontological evidence that the monotremes "retain
some of the traits that were lost in the...placentals". Carroll
points out that the skull morphology of the monotremes are highly
divergent from both placentals and marsupials:
"However, the phylogenetic position of monotremes remains subject to
debate. The skull of the platypus and echidnas are highly
specialized in a manner divergent from those of all other groups of
mammals, fossil or living." (Carroll, R.L., "Vertebrate Paleontology
and Evolution", W. H. Freeman & Co: New York, 1988, p420)
And there is no evidence that they benefited from "geograpic
isolation and lack of competition". The echidna for example is highly
successful:
"Echidnas live all over the Australian continent (and extend into
Papua-New Guinea), the only native mammal with such a wide
range....Echidnas come as two species in two separate genera and with
quite different habits. Tachyglossus aculeatus (the Australian form
with Papuan extensions) rips apart ant and termite nests with its
stout forelimbs and collects the inhabitants on its sticky tongue.
The larger and longer-snouted Zaglossus bruijni of Papua-New Guinea
lives on a nearly exclusive diet of earthworms. Moreover, three
other species, including the "giant" echidna, Zaglossus hacketti,
have been found as fossils in Australia. Echidnas are a successful
and at least modestly varied group." (Gould S.J., "Bligh's Bounty",
"Bully for Brontosaurus", Penguin: London, 1992, p285)
NM>As to Stephen's (and Denton's, p. 109 and thereabouts) point that,
>with monotremes, the individual characteristics are either reptilian
>or mammailian, I do not think that is a problem: why should all
>mammalian charactistics evolve at once?
This is so-called "mosaic evolution":
"Natural selection can work independently upon adaptive traits in
evolutionary sequences, changing them at different times and rates.
Frequently, a suite of characters undergoes a complete transformation
before other characters change at all. Paleontologists refer to this
potential independence of traits as mosaic evolution.' " (Gould
S.J., "Ever Since Darwin", Penguin: London, 1977, p58)
"Organs evolve separately in response to differing adaptive
requirements -a concept we call mosaic evolution...The concept of
mosaic evolution dictates that organs will evolve in different ways
to meet varying selective pressures." (Gould S.J., "Ever Since
Darwin", Penguin: London, 1977, p66)
"We would not deny Cuvier's inference today, but only his initial
premise of tight and ubiquitous correlation. Evolution is mosaic in
character, proceeding at different rates in different structures. An
animal's parts are largely dissociable, thus permitting historical
change to proceed." (Gould S.J., "The Stinkstones of Oeningen",
"Hen's Teeth and Horse's Toes" Penguin: London, 1984, p104)
"Evolution does proceed (as it must) by dissociating complex systems
into parts, or modules made of a few correlated features, and by
altering the various units at differing rates and times. Biologists
refer to this principle as `mosaic evolution,'..." (Gould S.J.,
"Mozart and Modularity", "Eight Little Piggies", Jonathan Cape:
London, 1993, p255)
But, as Johnson and ReMine point out, "mosaic evolution" is not
scientific because it explains everything (and therefore explains
nothing):
"For these and other reasons, orthodox neo-Darwinists prefer to
explain sudden appearance on the traditional basis of gaps in the
fossil record, and stasis as a reflection of "mosaic evolution" and
"stabilizing selection." The former means that the soft body parts
might have been evolving invisibly while the parts which fossilized
stayed the same. The latter means that natural selection prevented
change by eliminating all the innovations, sometimes for periods of
millions of years and despite changing environmental conditions that
ought to have encouraged adaptive innovation. Natural selection
appears here in its formulation as a tautology with rather too much
explanatory power, an invisible all-purpose explanation for whatever
change or lack of change happened to occur." (Johnson P.E., "Darwin
on Trial", InterVarsity Press: Downers Grove Ill., Second Edition,
1993, p53).
and
"The concept of "mosaic evolution," developed by Louis Dollo and
others, refuted the notion of harmonious development by affirming
that individual organs could have independent phyletic histories,
despite the evident correlation of parts within any organism.
(Gould, 1977, p234, my italics) Mosaic evolution is a wide open
concept. It does not shape our vision. It laces no constraints on
our expectations of nature. Since it allows anything, mosaic
evolution is not a scientific theory." (ReMine W.J., "The Biotic
Message: Evolution Versus Message Theory", St. Paul Science: Saint
Paul MN, 1993, p289)
Denton's point was that because the monotremes reptilian and
mammalian features were not transitional, but fully formed, there is
no evidence that they were acquired gradually as Darwinism
originally believed (before Mosaic Evolution was invented):
"Another classic example of an intermediate type is the egg-laying
mammals, the monotremes such as the duck billed platypus. In laying
eggs the monotremes are reptilian, but in their possession of hair,
mammary glands, and three ear ossicles they are entirely
mammalian....where they arereptilian in, for example, the
reproductive system and in the structure of their eggs, they seem
almost fully reptilian, while where they are mammalian, as for
example in the construction of their middle ear, or in the possession
of hair, they are fully mammalian. Instead of finding character
traits which are obviously transitional we find them to be either
basically reptilian or basically mammalian, so that although the
monotremes are a puzzle in terms of typology they afford little
evidence for believing that any of the basic character traits of the
mammals were achieved gradually in the way evolution envisages."
(Denton M., "Evolution: A Theory in Crisis", Burnett Books: London,
1985, pp109-110)
NM>Besides, the statement is not quite true: playpi do not have
>mammary glands in the same sense as placentals: the babies "lap
>milk from their mother's abdomen" rather than sucking on nipples, my
>trusty World Book Encyclopedia says.
I think you are getting "mammary glands" confused with nipples. The
platypus does have mammary glands:
"When the great naturalists delineated their positions and defined
the battleground, mammary glands had not been found in the female
platypus-an apparent argument for those, like Geoffroy, who tried to
distance monotremes as far as possible from mammals. Then, in 1824,
Meckel discovered mammary glands. But since platypuses never do
anything by the book, these glands were peculiar enough to spur more
debate rather than conciliation. The glands were enormous, extending
nearly from the forelegs to the hind limbs-and they led to no common
opening, for no nipples could be found. (We now know that the female
excretes milk through numerous pores onto a portion of her ventral
surface, where the baby platypus laps it up.)" (Gould S.J., "To Be A
Platypus", "Bully for Brontosaurus", Penguin: London, 1992, p273).
And the other monotreme, the echidna, does have both mammary glands
and nipples (not to mention a marsupial-like pouch):
"The pouch or incubatorium of the echidna appears on the ventral
surface in the females at the beginning of the breeding season which
lasts from early July to late September. There is equivocal evidence
that the period of gestation in the uterus is 27 days. After this
the egg is deposited in the pouch (no one knows how) and is incubated
there. The only recorded observation of a successful incubation
showed that at a pouch temperature of about 89 degrees F (32 degrees
C) this lasts 10-10 1/2 days. Since the body temperatures of
echidnas vary from 84 degrees -89 degrees F (29 degrees -32 degrees
C) (see below) it is possible that some incubation periods could be
longer or shorter than 10-11 days. The pouch egg has diameters of
about 0 75 x 0-5 in (16 x 13 mm). At hatching a little animal
looking most remarkably like a newborn marsupial, breaks out of the
egg by means of an egg tooth and attaches itself by clinging with its
relatively enormous forearms to one of two milk patches or areolae
found on the dorsal surface of the pouch. From the areola it sucks
milk secreted by the paired mammary glands which have the many-
chambered (alveolar) structure found in the mammary glands of other
mammals. (Griffiths M.E, "Encyclopedia of the Animal World", Bay
Books: Sydney, 7:620).
NM>Also, monotremes are not fully warm blooded - their body
>temperatures vary somewhat with the outside temperature (but not to
>the degree that reptile temperatures do) - if this is not a case of
>an intermediate trait, I don't know what is.
Reptiles are also "warm blooded" but they cannot regulate their
temperature directly:
"As reptiles pioneered in dry places it was not just the danger of
desiccation that they faced. Another big change that proved to be a
difficulty was the wild and capricious temperature range of the land.
By contrast, water, with its steady daily and yearly temperature
cycles, is an easy, even environment. Besides the need to guard
against loss of body water the new reptiles had to work out a way to
combat the vicissitudes of heat and cold ashore. A long time later
their descendants, the birds and mammals, were to do this by
balancing high production of metabolic heat with clever radiating
devices; but no living reptile is yet able to control its body
temperature in this way. For a long time zoologists supposed that
reptiles had no control at all over the body temperature, and that it
helplessly rose and fell with that of the surroundings. Reptiles
were, and until lately have been, spoken of as "cold-blooded"
animals. Now, primarily because of some shrewd researches of R. B.
Cowles and Charles Bogert, carried out during the 1940'S, this idea
has had to be abandoned. Reptiles are not at the mercy of the
temperature of the milieu. If they were, they would achieve little,
even by reptilian standards. Actually they can maintain a fair
control over their blood temperature, and they do this not by
controlling gain or loss of metabolic heat, but by moving around, by
alternately seeking and avoiding sunlight or warm ground. They
practise what is called behavioural temperature control, and some
species, at least, maintain their preferred temperature at a
remarkably steady level." (Carr A., "The Reptiles", Time/Life Books:
Netherlands, 1964, p85)
Mammals, OTOH, can regulate their own body heat directly:
"Certain other features, although not necessarily unique, contribute
to the mammals' dominance in the world. The most important of these
is warm-bloodedness. This ability to maintain a stable, or nearly
stable, body temperature while the temperature of the environment
varies over a considerable range makes mammals both adaptable and
enduring. In their capacity for heat regulation they are paralleled
by the birds, but differ greatly from the cold-blooded fishes,
amphibians and reptiles, whose body temperatures vary with those of
their surroundings. The extremes of temperature to which mammals can
be exposed without a change in the temperature of their own bodies
varies to some extent with different species." (Carrington R., "The
Mammals", Time/Life Books: Netherlands, 1965, p11).
The platypus can regulate its own temperature internally:
"The platypus is an elegant solution for mammalian life in
streams-not a primitive relic of a bygone world. Old does not mean
hidebound in a Darwinian world. Once we shuck the false expectation
of primitiveness, we can view the platypus more fruitfully as a
bundle of adaptations. Within this appropriate theme of good design,
we must make one further distinction between shared adaptations of
all mammals and particular inventions of platypuses. The first
category includes a coat of fur well adapted for protecting
platypuses in the (often) cold water of their streams (the waterproof
hair even traps a layer of air next to the skin, thus providing
additional insulation). As further protection in cold water and on
the same theme of inherited features, platypuses can regulate their
body temperatures as well as most "higher" mammals, although the
assumption of primitivity stalled the discovery of this capacity
until 1973-before that, most biologists had argued that platypus
temperatures plummeted in cold waters, requiring frequent returns to
the burrow for warming up." (Gould S.J., "To Be A Platypus", "Bully
for Brontosaurus", Penguin: London, 1992, p277).
Echidnas likewise are "warm blooded":
"Echidnas are , i.e. their body temperature is largely independent
of changes of temperature in the air around them. They regulate body
temperature mainly by control of the production of heat but
evaporative cooling and vaso-motor processes contribute appreciably
to the *temperature regulation." (Griffiths M.E, "Encyclopedia of
the Animal World", Bay Books: Sydney, 7:621)
While monotremes' heat regulation may be different from other mammals
(and that has not been established - some mammals hibernate for
example), it is not "intermediate" between reptiles and mammals, in
the sense being in the middle between "cold blooded" and "warm
blooded". Heat regulation is a complex package of features, including
body chemicals, perspiration through skin pores, shivering
response, regulation of blood supply, etc. Monotremes have it
all and reptiles don't have any of it.
NM>I admit that platypi lay their eggs in a fully reptilian manner -
>but echidnas (World Book again): "lay one egg a year. The egg has
>a tough, leathery shell and hatches in a pouch that forms on the
>female's belly each mating season. The young echidna remains in the
>pouch for several weeks and feeds on the mother's milk."
Agreed. Both the echidna and platypus egg(s) are fully reptilian:
"...monotremes are oviparous and that the segmentation of their eggs
is meroblastic. This means that the egg contains a lot of yolk, as
it does in birds and reptiles, and the cell within the egg sits on
top of the yolk. Only during development does this cell and its
descendants divide forming a thin cap of cells sitting on a mass of
yolk. In other mammals the egg is small and consists only of a cell
containing little yolk; during its development the whole egg cell
divides. This is called holoblastic segmentation." (Griffiths M.E,
"Encyclopedia of the Animal World", Bay Books: Sydney, 7:618-621)
NM>From a few creatures like this, it is impossible to reconstruct
>the exact sequence from reptile to mammal - but it does show that
>the existence of fully functional, natural intermediates is
>possible, and it suggests to us reasonable paths of evolution from
>one lineage to another that do not require supernatural explanation.
Diasagree. The monotremes are not "natural intermediates" in the
sense of having intermediate structures:
"Once again, the existence of stratomorphic intermediate groups and
species seems to be good evidence for evolution. However, the
stratomorphic intermediate evidences are not without difficulty for
evolutionary theory. First, none of the stratomorphic intermediates
have intermediate structures. Although the entire organism is
intermediate in structure, it's the combination of structures that is
intermediate, not the nature of the structures themselves. Each of
these organisms appears to be a fully functional organism full of
fully functional structures. Archaeopteryx, for example, is thought
to be intermediate between reptiles and birds because it has bird
structures (e.g, feathers) and reptile structures (e.g., teeth,
forelimb claws). Yet the teeth, the claws, the feathers and all
other known structures of Archaeopteryx appear to be fully
functional. The teeth seem fully functional as teeth, the claws as
claws, and the feathers as any flight feathers of modern birds. It
is merely the combination of structures that is intermediate, not the
structures themselves. Stephen Jay Gould calls the resultant
organisms "mosaic forms") or "chimeras." As such they are really no
more intermediate than any other member of their group. In fact,
there are many such "chimeras" that live today (e.g., the platypus,
which lays eggs like a reptile and has hair and produces milk like a
mammal). Yet these are not considered transitional forms by
evolutionists because they are not found as intermediates in
stratigraphic position." (Wise K.P., "The Origin of Life's Major
Groups", in Moreland J.P. ed., "The Creation Hypothesis",
InterVarsity Press: Downers Grove Ill., 1994, 227)
Even Dawkins agrees:
"In the taxonomy of living creatures these filing problems do not
arise. There are no 'miscellaneous' animals. As long as we stay
above the level of the species, and as long as we study only modern
animals (or animals in any given time slice: see below) there are no
awkward intermediates. If an animal appears to be an awkward
intermediate, say it seems to be exactly intermediate between a
mammal and a bird, an evolutionist can be confident that it must
definitely be one or the other. The appearance of intermediacy must
be an illusion." (Dawkins R., "The Blind Watchmaker", Penguin:
London, 1991, p260)
[continued]
God bless.
Steve
-------------------------------------------------------------------
| Stephen E (Steve) Jones ,--_|\ sejones@ibm.net |
| 3 Hawker Avenue / Oz \ Steve.Jones@health.wa.gov.au |
| Warwick 6024 ->*_,--\_/ Phone +61 9 448 7439 (These are |
| Perth, West Australia v my opinions, not my employer's) |
-------------------------------------------------------------------