If Monkeys Became Humans, Why Are Monkeys Still Around?

Reading Sapiens

Everything was making sense.

Humans evolved.

Neanderthals existed.

There were multiple human species.

Cool.

Then one thought entered my head.

And I couldn't continue reading.

This is how evolution existed in my head

Suppose there are 100,000 monkeys.

Every year they have babies.

Let's say every generation, 1% of monkeys evolve slightly.

So naturally I imagined this.

This felt perfectly logical.

Because monkeys are still reproducing.

So they'll keep producing monkeys.

Chimpanzees are reproducing.

So they'll keep producing chimpanzees.

Humans are reproducing.

So they'll keep producing humans.

Evolution should be happening continuously.

Almost like water flowing through pipes.

Monkeys → Chimpanzees → Humans

Forever.

Which immediately creates another question

If evolution never stopped…

Where are today's half-human chimpanzees?

Shouldn't there be…

97% chimpanzees?

98% chimpanzees?

99% chimpanzees?

Halfway humans?

Why don't we see the pipeline?

Then another contradiction

Scientists say…

Humans and chimpanzees came from a common ancestor.

Okay.

But then…

Where is the common ancestor?

Shouldn't it still exist?

Because while some families became chimpanzees…

the remaining families should still keep producing common ancestors.

Exactly like monkeys keep producing monkeys in my model.

Right?

Then another one

If humans evolved from chimpanzees…

Why haven't ALL chimpanzees become humans?

Evolution has had millions of years.

Shouldn't every chimpanzee eventually become human?

Then another

If Homo sapiens and Neanderthals both existed…

What happened?

Did humans kill every single Neanderthal?

How is that even possible?

Europe is huge.

Surely some tribe survived.

Then another

People say…

We still carry Neanderthal DNA.

Wait…

If that's true…

Why are we Homo sapiens?

Why not Homo neanderthalensis?

Or Homo sapiens-neanderthalensis?

Then another

Humans and chimpanzees share around 98-99% DNA.

Humans and Neanderthals share even more.

So where exactly do scientists draw the line called "species"?

At this point I realised

Every confusion came from one picture.

I imagined evolution like a conveyor belt.

Old animals stayed behind.

New animals stepped forward.

Like this.

But evolution isn't a conveyor belt

It's branching.

Here's what actually happens

Suppose there are 100,000 animals.

A mountain appears.

Now there are:

50,000 west

50,000 east

They stop meeting.

Generation after generation…

both populations keep changing.

Not dramatically.

Tiny changes.

Every child is almost identical to its parents.

Nobody notices anything.

Repeat for 300,000 generations.

Eventually…

Scientists look back and say

"This population became chimpanzees."

"This population became our ancestors."

No generation ever woke up saying

"I'm no longer the old species."

Which answered my biggest question

The common ancestor didn't disappear.

It slowly became…

something that wasn't the common ancestor anymore.

Exactly like Old English.

Nobody killed Old English.

Nobody stopped speaking it.

Every generation changed it slightly.

Until one day…

People realised they were speaking English.

Neanderthals suddenly made sense too

There wasn't one giant battle.

There were perhaps only a few thousand Neanderthals.

Small isolated groups.

Some died.

Some merged with Homo sapiens.

Some couldn't compete.

Some populations disappeared.

After thousands of years…

There were simply no separate Neanderthal populations left.

Only Homo sapiens remained.

But…

Pieces of Neanderthals still live inside us through DNA.

The picture that finally clicked

Evolution isn't

Monkey
↓
Chimpanzee
↓
Human

It's

One branch splits.

Both branches continue changing.

Both keep evolving.

Sometimes one branch survives.

Sometimes one disappears.

Sometimes one becomes us.

Closing

The biggest thing I learned from Sapiens wasn't a fact.

It was realizing that my mental model of evolution was wrong.

I thought evolution was a queue.

It turns out…

it's a tree.

And somehow, changing that one picture answered almost every question I'd been carrying since childhood.