[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Impacts and ETs
A relationship exists between the number of neurons possessed and the
cognitive ability of an organism.
I mean, of course it sounds logical, but it has never been tested. Even the
number of neurons _per total body mass_, which comes closer even though it
sounds less logical, does not seem to correlate 1 : 1 with any measure of
Still, while demonstrations of parrot and crow intelligence are
wildly impressive, they don't compare with human cognition...as far
as we can test it, anyway.
Well... that parrot is learning to read, with a brain the size of... perhaps
one of your eyes.
Neurons are the most expensive (energetically) tissue to create.
I don't know. They are, however, the most expensive one to maintain.
must make harder choices...e.g., marsupials must devote embryonic energy
to developing jaw and musculature for climbing and sucking at an early
age. Like some chromosomal conditions in humans, there are some very
smart marsupials...but, by an large, they are limited by this ontological
demand! For an egg layer, the longer one tends a nest in one location,
the longer that nest is at risk. This provides a pressure to vacate.
And, after hatching, a long period of precociality adds even more
of the same pressure. Hatchlings that fly or run immediately must be
under the same
developmental pressure as marsupials, i.e., physiological choices favoring
locomotion/coordination must be made.
I think this leaves archosaurs with only one option: develop safety and
ontological leisure time _in utero_.
I'm not so sure that vivipary is automatically safer than ovipary. An
immobile nest may well be at a similar risk as a mobility-impaired pregnant
female. I've already mentioned how marsupials get around this constraint.
Now consider the trademark misfeature of vertebrates: the birth
canal passes through the pelvis. We've reached the limit. We can't evolve
larger brains at birth anymore. Marsupials have no such limit. The pouch is
not constrained by bones.
I know we've talked about this before...but I can't remember why--or if
there are good hypotheses--why this was not done as far as we know in
The embryos of archosaurs... or at least birds... take the calcium they need
from the eggshell. Other animals store it in the yolk. I can imagine that
this makes archosaurs without eggshells impossible.
The one I do remember goes like this: lizards and other
_small_ reptiles have evolved similar structures independently and
repeatedly. But archosaurs were too big
I don't need to mention hummingbirds. Your average tiny croc --
Atoposauridae, for instance -- suffices.