Menneskeheten endrer seg.

Menneskeheten is the noun menneskehet with the definite ending -en attached.

• menneskehet = humanity / humankind
• menneskeheten = humanity, humankind, the human race in a general sense

So this is one complete noun, not a separate word plus an article.

That is very normal in Norwegian. Norwegian often uses the definite form where English uses no article at all.

So menneskeheten does not have to be translated literally as the humanity. In natural English, it is usually just humanity or humankind.

It is singular.

Even though it refers to all humans, it is a collective singular noun, like humanity in English. That is why the verb is singular too:

• Menneskeheten endrer seg. = Humanity is changing.

Because å endre seg means to change in the sense of undergoing change.

There is an important difference:

• å endre noe = to change something
• å endre seg = to change, to change oneself, to undergo change

So:

• Jeg endrer planen. = I am changing the plan.
• Planen endrer seg. = The plan is changing.

In your sentence, menneskeheten is the thing that is changing, so Norwegian uses the reflexive form endrer seg.

Seg is a reflexive pronoun. It refers back to the subject.

Here, it points back to menneskeheten, so the literal sense is humanity changes itself or humanity changes in itself. But in natural English, you usually just say humanity changes or humanity is changing.

So even though English often leaves this out, Norwegian needs seg with this verb in this meaning.

Endrer is the present tense of å endre.

So it can mean:

• changes
• is changing
• sometimes does change, depending on context

Norwegian present tense often covers both a general truth and something happening now.

Because Norwegian does not need a separate auxiliary here.

English often uses is changing, but Norwegian very often just uses the simple present:

• Menneskeheten endrer seg.

This can mean both:

• Humanity changes.
• Humanity is changing.

The exact meaning depends on context.

The word order is:

Subject + verb + reflexive pronoun

• Menneskeheten = subject
• endrer = verb
• seg = reflexive pronoun

This is the normal main-clause order in Norwegian.

If something else comes first, the verb still stays in second position:

• Nå endrer menneskeheten seg. = Now humanity is changing.

Yes, but it means something slightly different.

• Menneskeheten = humanity / humankind as a whole
• menneskene = the humans / people

So:

• Menneskeheten endrer seg. = Humanity is changing.
• Menneskene endrer seg. = People are changing.

The first sounds broader and more abstract.

Yes, historically and grammatically it is a feminine noun in Bokmål, like many nouns ending in -het.

But in Bokmål, feminine nouns are often also written with common-gender-style forms. That is why menneskeheten is completely normal and standard.

You may also encounter feminine-style patterns with other nouns, but for learners, menneskeheten is the important form to recognize and use here.

A rough pronunciation guide is:

• Menneskeheten ≈ MEN-nes-ke-heh-ten
• endrer ≈ EN-drer
• seg is often pronounced somewhat like sai or sei in everyday speech, though pronunciation varies by dialect

So the whole sentence is roughly:

MEN-nes-ke-heh-ten EN-drer sai

The exact sound of seg varies a lot across Norway, so do not worry if you hear different versions.

Yes. It is a fully natural and complete sentence.

It sounds like a general statement, for example in a discussion about history, society, technology, or culture:

• Menneskeheten endrer seg.
• Humanity is changing.

Short sentences like this are very common in Norwegian when making broad observations.