Each human is randomly unique because:
- Genes reside on chromosomes.
- Humans have 23 pairs of chromosomes.
- Each member of a pair of chromosomes are not identical.
- Egg and sperm cells under go a division (meiosis) that leaves each of them only one half of the chromosomes.
- The fertilization process is a random scramble with no order as to which of the egg’s 23 half-chromosomes combines with a separate set of 23 in the sperm.
- From gene to gene, one will be dominant and the other recessive.
- Changes (mutations) may take place in numerous parts of the process. This also tends to be random.
- The result of a successful conception is a zygote that developed into a human being.
This is called Mendelian inheritance.
It’s no accident that the randomness involved in the genetic making of humans is associated with Augustinian monk Gregor Mendel who figured all this out using the pea plants he grew in Moravia. Those interested in more are recommended to: Introduction to genetics.