Originally posted by BlackJackal
Why do fish swim by swishing their tails from side to side rather than up and down like a whale?
Because of evolution, not because of geometric constraints.
These are the type of primary things that the DNA neural net
no 'DNA neural net'. THe author seems to be ascribing sentience to 'natural selection' itself.
Evolution is the mechanism by which the nature forms inanimate matter into people by throwing various animals at their environment to see if
This is purely speculation, that natural wants to make humans, and does so by attempting lots of different forms agianst the environment.
but they will always have major characteristics in common ... because ... these are fixed early on in evolution.
The problem is, that we have organism of 'this' general type because the major body plans were 'set' early in history. But this is because of
what gould refered to as 'contingency'. There was a wide variety of body types in the cambrian, only a few survived. This means that those other
body types are generally lost to the planet, and that the few that are left are the ones that have to fill all other niches. So all animals today
have heads with eyes and noses and limbs and the like, because all animals are stemming from the same basic source. When you get to 'behind' that
source, to more primitive types, and follow the alternative types up the 'tree' you get types that are entirely different.
So its because of the 'randomness' of whatever was going on in that bygone era that entire bodyplans were completely wiped out, and only a small,
essentially random, set survived.
Evolution must proceed till it produces a being capable of turning it off.
? Evolution can be stopped by the destruction of life also. Indeed, even if man could somehow stop his own evolution, evolution would still be going
on in all the other populations of living things. This is a rather strange statement.
We then have only variation on the same theme adapting to small changes in the environment or in the animals themselves
This is because of things precisely like what's been discussed. Life expands to fill niches, and populations can change so long as there aren't
contstraints on it, phyiscally. So in the beginging, when there were little constraints, there were lots of differnet body plans out there in lots of
different animals. Then there was competition and the dangers of existence, this wiped out some groups, and others expanded. Those expanding groups
couldn't completely change their entire body plan into something else, because they are 'constrained' to work with the ones they have, not because
of some 'neural net' that says 'well you're an animal with segements and a well defined head, you can't become anything else'. And then once we
have that, of course the ensuing variation will be variation upon that theme and not be as drastic as it was when there were less contraints.
Occurs I know one is a mammal and the other one a fish.
This is why they have different movements, not because of some 'neural net'.
There are two things operating here, developmental constraints, and environmental constraints. Anything living in the water is constrained by the
phsyics of moveing thru water. Hence fish, sharks, whales, even sea going reptiles like icthyosaurs, have the same generalized shape, because to get
thru water, you need things like paddles and a streamlined shape etc etc.
are control by their 'developmental' constraints. Fish and sharks, for example, move their whole bodies side to side,
because thats a good way to move in water. Icthyosaurs and whales, however, evolved from land dwelling animals, where floping around like a leggless
fish doesn't get you anywhere. So in their historical development, their ancestors developed legs, and their body muscularture developed in such a
way that the body flexes the spine up and down, to go along with the movemetn of the legs. When land animals return to water, its not a simple thing
to get past this; their bodies are thus constrained. So after a long while developing for movement in the water, they get fish like tails and
paddles, but they move the tails up and down, because of this ancestral constraint. Its the same reason why they don't re-grow gills, or why they
don't lay fish like eggs. And its the same reasons why the paddles of land animals that adapted to the ocean are different that the unorganized spiny
rays and fins of fishes. Becuase evoltuion has to work with what its got.