Largest single digit Prime number.

Arithmetic uniqueness.

Independent number - neither generated by nor generates any other number between 2-10.

We are all veritable reproductions of matter - solid, liquid, gas, plasma, Bose-Einstein condensate, Quark-Gluon plasma and Degenerate matter = 7

All living things possess seven functions that are common - Locomotion/Movement; Sensory Perception; Nutrition; Growth; Reproduction; Respiration; Excretion/Secretion - all these separate the living from the non-living.

Seven is not more prevalent or less but because the question centers around human beings, and because of the innate instinctive satisfaction and security we draw by molding everything as a function of 7 it feels as if it is the most abundant number. This is a neurosensory phenomenon known as frequency illusion or more technically Baader-Meinhof phenomenon. Casino owners, gamblers and street hustlers have been using it for a very long time.

Since in the pre-rational era astronomers found seven planets in the solar system, they associated the number to some sort of divinity, which no matter how absurd appears today, had sown the seed of us becoming predisposed with seven and ever since we have had only subconsciously attempted to understand nature through the simplicity of seven.

More importantly when ancient people assigned the names of the day of one week to the then only known heavenly bodies, it changed from one 8-day week of the Ancient Roman Calendar to a 7-day week around 45 BC according to the Julian Calendar - Moon, Mars, Mercury, Jupiter, Venus, Saturn and Sun. There are 12 lunar cycles in a time frame of one year, and hence 12 month annual calendar was introduced instead of archaic ten (the winter produced nothing and hence had no name previously) to coincide with the crop cycle. But because Julian astronomers had already formulated a seven-day week by honoring the seven heavenly bodies, and also because a lunar cycle takes roughly 29-30 days, the best option was to divide it by 7 to get a more or less 4-week long month.

It is because of our absolute dependency on 7 in terms of dividing our work schedule/energy and livelihood as well as sustenance, 7 became ingrained into the collective psychology of the civilization and its association through the frequency illusion grew to a a point where human brains can only perceive natural phenomenon as functions of 7, as instinctively it feels more orderly and stable.

I honestly hope that I have shed some light on your query.

Phani,

> "It is known to us that light consists of seven colors,..."

This is not universally true.

There are many human societies with far fewer 'fundamental' colours.

http://theconversation.com/languages-dont-all-have-the-same-number-of-terms-for-colors-scientists-have-a-new-theory-why-84117

> "there are seven tunes in a song..."

This would be news to most musicians. Can you give evidence for this restriction?

> " seven stars "

There are many more than seven stars known to us.

>" seven days in a week "

And other schemes have been proposed. There is nothing in nature that requires there to be a periodicity of seven days.

> "physical and chemical properties are repeated after seven elements "

And how do you propose to categorize the actinides?

Lithium is a little like sodium.

Li atomic number = 3

Na atomic number = 11

(11 - 3) != 7

Abhishek Mukherjee hits the nail on the head - this is a societal matter with no origin in the physical world.

So true Prof. James Garry

Its all vagaries of perception by the human brain trying desperately to justify and rationalise all its neuroelectrical interpretations of the nature through only abstraction.

Thanks for nice explanation to all scientists/Profs