How have our languages changed?

Once upon a time, the human race spoke a single language. This language was Sanskrit or ancient Hindi. Then something happened and our languages ​​split apart. You could say we dispersed to different regions. That's why we came up with different words in different geographical regions. But why did we start using a different word for “pen”, my friend? Why did we name it completely differently? If the word pen, for example, had evolved into "pan" or "pin", I would understand that. At least if there are similarities, if there is a change with small nuances, I would understand that, but otherwise it is ridiculous.

In religious texts;
In the Torah, this event is referred to as the Tower of Babel.

Genesis 11:1-9 (summary) :
"The whole world was speaking the same language.
The people settled in the land of Shinar (Babylon) and decided to build a tower that would reach the sky.
The Lord saw their arrogant behavior and said:
'One people, one language... No matter what they do, nothing will be impossible for them anymore. ' Then God confused their languages ​​so that they could not understand each other.
So they dispersed throughout the earth and stopped building the tower.

The Quran says:

"The creation of the heavens and the earth, and the diversity of your languages ​​and colors, are among the signs of Him (Allah).
Indeed, there are lessons in this for those who know.
“O people! We created you from a male and a female. We divided you into nations and tribes so that you would know each other and take care of each other.
It says this, but it does not talk about how this change and transformation developed.
How have our languages changed?
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