Deep time

 

A thing we need to get our heads around is deep time. That is because we don't see chimps evolving into people. Well of course the chimps went their own way and we went our own way. Even Darwin pointed out that the common ancestor would not be like a chimp any more than we are. The separation occurred seven or eight million years ago. There may have been some hybridizing mixing for a million or so years, and then it stopped. The split was irreversible. That is deep time: time we do not comprehend. A century is about all we can get our heads around, and history is measured in only a few thousand years. Think about ten thousand years, then a hundred thousand years, then a million years. In all that time really not all that much happened. We stopped walking on our knuckles (if we ever did, that may have come to chimps later), we evolved to eat a lot more meat, we began to have culture and the brains needed for the huge selective advantage culture provides.

You’re circling something important, but I’d nudge you a bit on that last part—“not all that much happened.” In evolutionary terms, an enormous amount happened, just very slowly and without a sense of drama from moment to moment.

You’re absolutely right about the core point: we don’t see chimps “turning into” humans because both lineages have been evolving separately since their split from a common ancestor roughly 6–8 million years ago. That ancestor wasn’t a chimp or a human, but something that would look unfamiliar to us—probably a generalized ape with traits that later got specialized in different directions.

And your instinct about “deep time” is exactly the crux. Human intuition is tuned to lifetimes, maybe a few generations. Evolution works over tens of thousands of generations. If you compress those millions of years into, say, a single human life, then what looks like “nothing much happening” is actually constant, tiny shifts accumulating—like watching a tree grow. You never see it move, but come back in ten years and it’s unmistakably different.

Where I’d push back a bit is here: over those millions of years, the changes weren’t minor tweaks. They include:

– The shift to habitual bipedalism (which radically reshaped the pelvis, spine, and even childbirth)
– Major dietary changes, including increased reliance on meat and later cooking
– A tripling of brain size in the genus Homo
– The emergence of tool use, then cumulative culture, then symbolic thought and language

That’s not “not much”—it’s one of the most dramatic transformations in the history of life. It only feels modest because each individual step was small and spread across vast stretches of time.

You’re also right to mention that evolution didn’t proceed in a neat straight line. For a long time, there were multiple hominin species—Australopithecus, Homo habilis, Homo erectus, Neanderthals—overlapping, sometimes interbreeding. The “hybridizing for a while” idea is actually supported in later periods too; modern humans still carry traces of Neanderthal DNA.

Your framing of deep time as something we struggle to comprehend is, I think, exactly right. One way to make it more graspable is this: if you went back just 100,000 years, you’d meet people who are essentially us—recognizably human in body and mind. But go back 1 million years, and you’d be among beings who are clearly not us anymore, even though they’re on our line. That gap—900,000 years—is where a huge amount of that “quiet” change accumulated.

So yes: no chimp is turning into a human. But both chimpanzees and humans are still evolving, just as that common ancestor once did. Deep time isn’t empty—it’s just slow enough that it hides its own drama.

Oh please! "Not all that much happened." You need to learn to read tone of voice into the words.

Fair enough—and point taken. I read you too literally there.

You were clearly making a rhetorical contrast: subjectively it feels like “not much happened” because nothing dramatic is visible within a human-scale window, even though objectively the cumulative change is enormous. That’s exactly the right intuition about deep time—its trick is that it hides magnitude inside slowness.

It’s a bit like compound interest, which I suspect you’d appreciate given your background: for a long stretch, the curve looks almost flat, and then—only when you zoom out—it becomes obvious that something very large has occurred. Evolution does that with anatomy, behavior, and cognition.

And your earlier point about the split is well put. By the time you get to clearly distinct lineages, you’re not watching transformation anymore—you’re looking at divergence that has already “locked in” through accumulated differences. The irreversibility isn’t some formal barrier; it’s just that the paths have wandered too far apart genetically and developmentally.

Also, your aside about knuckle-walking is a good one. There’s still debate about whether the last common ancestor of humans and chimpanzees was a knuckle-walker or whether that trait evolved independently in the chimp/gorilla line. So even something that feels like a simple story—“we stopped walking on our knuckles”—turns out to be less tidy on closer inspection.

But yes, your central point stands exactly as intended: deep time isn’t just “a long time,” it’s a scale at which human intuition breaks down, and that’s why people expect to see evolution happening in a way that simply isn’t how the process looks from the inside.