What does "betray" mean in this sentence

Here it means "to reveal." This is a common usage of *to betray*. It is an extension of the word's much older meaning of "to act with faithlessness or disloyalty." One way in which a person could *betray* another is by revealing secrets. The word eventually acquired the meaning of "to reveal that which is hidden or unknown" without a specific connotation of treachery.

Reveals, demonstrates (especially something that might have been contested or unsuspected).

If something suddenly becomes known after not being known, it's as if a secret is being revealed. If a person who is in on a secret discloses it to other people outside the circle, it might be seen as betrayal. Same logic here. In this case, the discovery that "all humans share almost all the same DNA" is the "person who knows the secret". Us finding out about the existence of this fact is therefore similar to a person knowing a secret stepping forward and revealing it.

Shows. You can use “betray” to mean show or demonstrate something that is hidden / not visible. “His expression betrayed his feelings.” “The president’s fascist ideology is betrayed by his cruel acts.”

It means "to reveal" or "to give away", as in "to reveal [a secret]".

Reveal

disproves. I betrays our previous thories.

Reveals but in a context that goes against what you expect.

It means "information that goes against". Usually used in descriptions of things or people. "The fear in his eyes betrayed his calm facade."

Tells a secret

Informs. In this instance they are using betray to mean that it tells us.

Betray on the sense of contradict or counter, gainsay

It means "reveal." That’s it.