How many different people?

Knowledge is never enough for seekers and never accurate of believers

Disclaimer — it might be technical with some calculation. In case you hate either or both, wait for another post! :)

First, let’s start with basics — Suppose you have been given 3 colors of ring and asked, how many ways you can put these rings in your right hand (given that you’re not allowed to wear more than one ring at a time).

Simple, try each color in each finger of the hand. So the answer is, 3 x 5 = 15

Generically speaking, if you have X things where variation of each thing independently possible is (N1, N2, N3, N4… NX), then total variation of such thing possible = N1 x N2 x N3 x N4 … NX.

For e.g. in case of binary numbers, let’s suppose X = 3 and since we know N1 = N2 = N3 = 2, different variations possible = 2 x 2 x 2= 8, i.e. 000, 001, 010, 011, 100, 101, 110 and 111.

Now, let’s come back to the topic — How many different type of people possible!

Let’s imagine a hypothetical world where any human is known by its number of eyes and number of fingers. Assuming that number of eyes possible for these humans can be 1 or 2 and number of fingers can be any number between 0 and 10. Number of unique humans possible = 20

Now taking one step further, let’s try to calculate number of unique faces possible for homosapians with some assumptions as mentioned:

1. Face includes eyes, nose, lips, cheeks/jawline, hair, ear, and (ofcourse) color. i.e. things like tongue, teeth, etc. which are not directly visible is not taken in scope.
2. Let’s say a normal human can only identify up to 10 different types of eyes. To understand this better, if you have been shown only eyes and asked to re-identify them uniquely, your brain can only identify up to 100 different type of eyes before you start getting confused.
3. Similarly, let’s assume the following variations of other parts:
   a. Nose — 10
   b. Lips — 10
   c. Cheeks/Jawline — 15
   d. Hair — 10
   e. Ear — 10
   f. Color — 10

If you think it’s a lot of variation for each part, wait for what’s coming up below. If you think that these variations are less, consider going through your friend list in Facebook and find if there is a substantial difference in assumptions. Also, before reporting it, try to think if your brain can actually process all the variations, or it will get confused.

So, how many people you can uniquely identify by face? Simple, multiple each variation = 10 x 10 x 10 x 15 x 10 x 10 x 10= 15,000,000.

If you’re able to uniquely identify 15 million faces, then:

1. You have god-like skills
2. Given world population of ~8 billion people, ~2 people in every 1000 people looks same.

All of these might sound irrelevant but then if you take a step back and think, even though every person can be thought as different (appearance-wise, for e.g.), they are not so practically different.

It’s just weird that we try to find different face, but eventually we are ending up finding similar face!

Update: Here’s an interesting video about unique face recognition and it’s practical use in modern world.