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Re: Mammalian success and egg predation,
On Wed, 12 Jun 1996, Martin Baeker wrote:
> This is not a detective story where we can find the murderer by
> asking: Who got the most out of it?
No, it's actually a serial killer or sequence of several killers. And just
like the real police, you look for a pattern in the killings in order to
solve the "crime." And maybe we can conclude that the killers had less
to do with the crime than the victims. I mean, if the victims
insist on offering such easy crime opportunities, we should, perhaps,
blame the victims!
> BUT live-bearing is by far not the only difference between mammals and
> the rest of the world, so this seems to me to be a very weak statement.
> Any flaw in this line of thinking?
Yes. It is a critical difference. Listen to John McLaughlin from
_Synapsida_ (he's actually talking about escape from egg-laying for
mammals--but I believe it applies to all egg layers): "Eggs are highly
fragile objects, the most vulnerable interval in an egg-layer's life style."
Why do I give so much importance to this particular aspect of
dinosaurian existence? I do this because perhaps the most
rigorous rules, the most strictly enforced by Nature, are those
which come into play at that most critical time: when an organism
reproduces itself. Reproductive success is the gold standard of
natural selection, the only currency it recognizes. The perfect
organism which fails to relay its genes to the next generation
is, in terms of natural selection, an abject failure. And yet,
inevitably, it is at exactly this time of hereditary transmission
that we living things are most prone to hazard! Our eggs,
larvae, embryos, and juvenile stages are defenseless, they are
very sensitive to physical forces, and they are tasty. Seen from
the perspective of the genes as they make their way from one
generation to the next, the reproductive stages are a kind of
gauntlet of ravaging selective forces. The rigors of
reproduction have been played out in phylogenetic history.
Together, the rules of natural selection and the savoriness of
offspring have written the story of the succession of animal life
from sea to land: amphibians were able to exploit the terrestrial
environment but were still utterly dependent on bodies of water
for one aspect of survival--their reproduction; some adapted a
solution to this problem and became reptiles--the amniotic egg
and internal fertilization afforded aquatic independence and
allowed them to dominate the land. I believe (but Ron Orenstein argues
well against me) that placental mammals are a further development
along these lines--even a progression! That doesn't mean that frogs
become extinct, nor reptiles. But for the big open-field niche, I
believe the new form was more fit. But it wasn't only
the animal kingdom, the phylogenies of plants are also defined by the
various reproductive tactics and, indeed, reproductive security is a
recurring theme here as well!!!
And the connection between the two points, i.e., post K/T mammal
success and dinosaur extinction is this: mammals may have parasitised
dino nests along with birds, lizards, crocs, and other dinos. This may
have led to a subtle or drastic decrease in dino birth rates. But inasmuch
as mammals were secure reproducers, they were winners, even if not in tooth
and claw, in the battle for differential reproductive success. And their
secure reproduction kept them competitive after the K/T as well.