THERE'S NO DUPLICATE OF WHO YOU ARE...YOU ARE UNIQUE AND DIFFERENT.
There cannot be perfect duplicates that are exactly like each other in every way, not just biologically, but in every way and in every sense. This is impossible, and can only exist in imagination and in fiction.
It is not even remotely possible that ‘perfect duplicates’ could have ever existed in the past or can ever become a possibility in future; not even across time covering millions of years. There can however be ‘near-duplicates’ who may resemble each other to a marvelous degree and absolutely indistinguishable from each other, but with some imperceptible or unrecognizable difference.
Perfect duplicate in this context does not mean identically biological duplicates alone, but duplicates in every sense, like thoughts, emotions (perfectly duplicate emotional or astral bodies and perfectly duplicate mental bodies). Perfect duplicate in this context also means identical consciousness.
People are not just their physical body, but a life essence as well that occupies the physical body during one’s life-time. This life essence (or Soul) can never be the same for two people. And, Souls have different spiritual ages and different baggage of different karma. So, the expression of the consciousness will necessarily be different, making the look-alikes different.
These differences, together with the difference in thoughts and emotions, difference in the air breathed, food, and so on will surely bring about changes in the physical body too. These changes may be imperceptible, unnoticeable, but they will certainly change the biological get up at a cell level, resulting in some type of mutation.
So at birth, even if two individuals are perfect duplicate (biologically), they will become different immediately. They can never even sustain perfect biological replica of each other. And, even at birth, as the two Souls are never identical, the difference is already there. Their inner intelligences and actions (and resultant reactions) will make them different too as time goes by. So perfect duplicate is never possible in reality.