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Campbell Biology says:

A typical prokaryotic cell has about 3,000 genes in its DNA, while a human cell has about 21,300 genes.

If evolution depends on random mutations occurring in the genome, this means that only certain genes are altered, but not add up to the total number. Supposing that we and the bacteria come from a common ancestor, then what is responsible for the tremendous amount of genes that has been added throughout the evolution?

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    $\begingroup$ "If evolution depends on the random mutations occurring in the genome, this means that we only alter certain genes, but not add up to the total number" - Why? Are you thinking only of point mutations? Also note that bacteria and humans have been evolving for the same length of time, and bacteria have had far, far more generations to evolve than humans have. $\endgroup$
    – Bryan Krause ♦
    May 27 at 15:05
  • $\begingroup$ "Are you thinking only of point mutations?" - This is the case, mutations are the only thing I can think of right now. Can you point out other factors? $\endgroup$
    – Georgi Popov
    May 27 at 15:15
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    $\begingroup$ I didn't say "mutation", I said "point mutation". You may even only be thinking of specifically substitution mutations. You could start with en.wikipedia.org/wiki/Mutation to learn about others. $\endgroup$
    – Bryan Krause ♦
    May 27 at 15:16
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    $\begingroup$ Look up gene duplications, copy number variations and transposons. That may give you a clue. $\endgroup$
    – user438383
    May 27 at 15:16
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    $\begingroup$ For a less mechanistic and more theoretical view, I would suggest looking into the evolution of complexity (that's just one ref it's a large literature). Obviously expanding to a view of mutation beyond substitutions is essential, as suggested by other commenters. $\endgroup$
    – Maximilian Press
    May 27 at 15:42

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