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Why evolution by natural selection didn't make use of RF?

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Kim Christensen:
Can't think of a "filter" that only passes a 3Khz sine while ignoring the 3Khz harmonic from a 1Khz squarewave. But I can imagine a "detector" for a pure 3Khz sinewave. Basically a 3Khz filter, x2 RMS detectors, and comparators to compare the energy at 3Khz vs everything else.

But on the topic of organic RF, I don't think there's any creature that outputs electrical pulses with sufficient rise time to emit enough RF energy to be useful for anything.

TimFox:
"RF" is a definition of a subset of electromagnetic radiation frequencies, not a physical definition such as "alpha particle radiation".
Different sources define "RF" starting somewhere between 3 to 10 kHz and ending somewhere between 1010 and 1011 Hz.
The FCC defines radio-frequency "RF" as between 3 kHz and 300 GHz and "microwave" as between 1 and 30 GHz.
Traditional subsets of RF use "3", since they were originally defined in terms of wavelength (in meters).
3 to 30 kHz is "VLF"
30 to 300 kHz is "LF"
0.3 to 3 MHz is "MF", where the broadcast band lies
3 to 30 MHz is "HF", called short wave
30 to 300 MHz is "VHF"
0.3 to 3 GHZ is "UHF"
until we reach 30 to 300 GHz, which is "extremely high frequency" EHF.
There are names for the decades below 3 kHz and above 300 GHZ.
The IEEE, NATO, and other agencies have other nomenclature, including the confusing radar bands (X, Ku, etc.).

Kim Christensen:
Sure that's fine... But how would a creature effectively radiate or receive "RF" in the VLF, LF, or even MF bands? Giant organic loopstick? It would have to be a very big animal.

TimFox:
I was just pointing out what "RF" is:  many postings above were about other electromagnetic fields or frequencies, such as visible light or the Earth's magnetic field.
Nobody mentioned how modern man, with metal fillings in his teeth, supposedly can demodulate and hear MF broadcast radio fields.

CatalinaWOW:
It seems to me possible that RF detection capability could have developed, but it is highly unlikely.  And full blown RADAR even less likely.  For a whole series of reasons.

Any capability that is retained by evolution has to provide some benefit (or at least do no significant harm) to survival.  So any systems which randomly occur must either be biologically nearly free, or provide significant benefit.

In my limited understanding all of the extant sensing systems started with a sensing capability, and then in some cases a transmitting capability came along later.  The oldest appear to be chemical, temperature and light sensing systems which began providing very simple approach or avoid data.  Quite useful to mobile organisms looking for food or avoiding hostile environments. 

In the entire spectrum from VLF through X-rays the highest power level on earth occurs in the visible spectrum and also has a very simple signal correlated to some biological survival (daily on-off).  So it is easiest of all to detect and is useful.  For reasons explained in several other posts detecting other bands is generally more difficult, and the immediate survival benefit is less obvious.  All subsequent development of vision systems are just riffs on this theme, with transmitters (various luminescence schemes) and modulators (colors and color changing capability) developing long after vision systems had become quite complex.

This theme occurs in all other sensing systems I am aware of.  Something simple with a strong available signal to detect that is survivability related happens and then gets elaborated over tens of thousands of generations. 

RF has at least three strikes against it.  Low ambient power.  Difficult detection.  And little obvious survivability benefit. 

Radioactive detection similar.  The strongest strike against it is that natural radioactivity strong enough to effect breeding success is extraordinarily rare. 



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