## Re: [GP] Plane of symmetry

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• ... Suppose you are communicating over a noisy channel; how do you ensure that aq message has been reliably transmitted ? One way is to use redundancy, by
Message 1 of 14 , May 21, 2003
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Varun Aggarwal <varun.aggarwal@...> writes:

> However I didnt clearly understand one of the responses...
>
> "If a potential mate is symmetrical, they have expressed their genes
> twice and got the same answer each time. If they are unsymmetric,
> they have either had an accident or have an underlying genetic
> problem. Either way a symmetric mate is a better bet than an
> unsymmetric one."
>
> How is a symmetric mate a better bet than an assymetric one?

Suppose you are communicating over a noisy channel; how do you ensure that
aq message has been reliably transmitted ? One way is to use redundancy,
by repeating the message so that its recipient can check how well the two
copies agree with each other.

Now assume you are using a "comma-free code," i.e., there are no natural
punctuation delimiters; how do you know when a message has even _ended_ ?
One way is to transmit a message follwed by its reverse, so that the total
redundant message forms a palindrome. (For example, DNA regulatory regions
are very often "reverse palindromes" --- a signal followed by its reversed
complement.) Since long near-palindromes are unlikely to occur by chance,
if you receive one, it's good indicator that the signal was a message
that has been corrupted by only a small amount of noise, with the degree
of asymmetry being an indicator of how bad the noise is.

Note, finally, that a neural network to recognize symmetry is fairly easy
to construct, so it is not surprising nature has exploited symmetry as a
"checksum" for mate selection.

-- Gordon D. Pusch

perl -e '\$_ = "gdpusch\@...\n"; s/NO\.//; s/SPAM\.//; print;'
• Meta 2 cents: I personally think this thread has relevance to GP and I m happy to see it here. On symmetry: I think Braitenberg s beautiful book Vehicles
Message 2 of 14 , May 21, 2003
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Meta 2 cents: I personally think this thread has relevance to GP and I'm
happy to see it here.

On symmetry: I think Braitenberg's beautiful book "Vehicles" (MIT Press)
provides some simple but important insights about the role of symmetry in
body design (at least).

-Lee

At 8:02 PM +0530 5/21/03, Varun Aggarwal wrote:
Hello

Thanks for all the responses. They were an interesting read and have given
me new directions to think. However I didnt clearly understand one of the
responses...

"If a potential mate is symmetrical, they have expressed their genes
twice and got the same answer each time. If they are unsymmetric,
they have either had an accident or have an underlying genetic
problem. Either way a symmetric mate is a better bet than an
unsymmetric one."

How is a symmetric mate a better bet than an assymetric one?

I had no intentions to take the group to something which doesnt concern gp.
However, if I am right natural selection for algorithms and algorithms to
understand natural selection complement each other, so can this come in the
bracket of GP. Please let me know.

Thanks
Varun

----- Original Message -----
From: <mailto:M.Sewell@...>Martin Sewell
To: <mailto:genetic_programming@yahoogroups.com>genetic_programming
Sent: Tuesday, May 20, 2003 4:36 AM
Subject: Re: [GP] Plane of symmetry

At 23:57 18/05/2003 +0530, Varun Aggarwal wrote:
>I was just wondering that all animals we see have a single plane of
>symmetry (some might have more) in their external appearance (though
>plants dont have).
>
>Any answers why nature evolved symmetric structure, that too mostly with a
>single plane of symmetry, and that too only externally.

At 12:01 19/05/2003 +0100, Norman Paterson wrote:
>If a potential mate is symmetrical, they have expressed their genes twice
>and got the same answer each time. If they are unsymmetric, they have
>either had an accident or have an underlying genetic problem. Either way
>a symmetric mate is a better bet than an unsymmetric one.

The above is true and concerns sexual selection which, as a special form of
natural selection, is not sufficient to answer the question of natural
selection.

>Plants don't choose mates by appearance. Appearance is only skin deep, so
>internal symmetry won't get you a mate.

Insect-pollinated flowers have large, coloured, scented petals (and nectar)
in order to attract insects.

Cheers

Martin

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