Re: why do we look the way we do?

Jonathan:
    
     Sorry for the delay, this question disappeared in my inbox.  You pose 
an interesting question, which has a couple of answers/thoughts.  First, 
you are also asking in a way, that if we rewound the tape, would we get 
the same result in the end, and the answer to that is probably not.  There 
would most certainly be bacteria and complex organisms, something akin to 
mammals perhaps, but humans for humans sake might not exist.

     Evolution doesn't necessarily strive to make the most energy 
efficient shapes, there is nothing as awkward as a sloth, or a hippo out 
of water.  Most of the changes that occur with evolution are stochastic in 
nature and there is as much pressure to keep advantageous traits as to not 
discard ones that cause no harm.  The existence of creatures in the past, 
on a geologic time scale, like dinosaurs, is again, not a consideration of 
energy efficiency per se, but overall efficiency of the organism to 
survive and reproduce.  If we look at the components of cells that 
actually make energy, the mitochondria in eukaryotes, and more 
specifically the F1/F0 ATPase, which actually makes ATP from the proton 
gradient in eubacteria and prokaryotes we can measure how 'efficient' this 
machine is, (It is actually a motor) and it is one of the most efficient 
rotors on Earth.  Bacterial motility by flagella is also an extremely 
efficient process.  If you think about how little food you actually need 
in a day to survive, it is actually amazing how well we process carbon 
sources into energy. 

     As we can clarly witness from the amazing diversity of life on the 
planet, there is no 'correct' structure, and many organizational patterns 
work from single-celled to organisms as complex as frogs and humans.  I 
encourage you to read the first few chapters of any biology text, or 
biochemistry text on phylogeny and evolution to appreciate the amazing 
ability of nature to try a nearly endless number of possibilities.

Thanks
   
 -Matt-