Joel:

I believe the invention of technology was a more important milestone than any specific application of it...especially when the archaeological record indicates that things started changing rapidly (in relative terms) soon afterward.

Daniel:

I'll be putting the pieces together both as I go and in the conclusion, but yes, those are important elements.  You're getting a bit ahead of me, which is good because it means I've clearly presented the information so far.

Howard:

So far the earliest evidence for use of fire is perhaps 1 MYA -- and it's sparse until much later, meaning that it's unlikely we depended on it for cooking or had the ability to create it at will, vs. using it when we came across it.  Grass and brush fires are reasonably common in grassland Africa.

Making fire with percussion is a much more complicated problem than making a sharp rock.  It's quite difficult, as anyone who's ever tried it can attest, and that's with a pre-chipped flint -- and steel (and where would one get steel?  In the wild one would require some sort of pyrite...another rare type of rock), not to mention things like tinderboxes full of charred cloth.  There's a reason survival kits contain magnesium or mischmetal instead.

Remember, the pace of progress was slow back then.  Tt took nearly a million years for our ancestors to figure out how to sharpen both sides of a rock (Oldowan vs. Acheulean industry -- this is a bit of an oversimplification, but not much.)    

I'll discuss this subject at length in the future.

Lauren:

Absolutely.  The population genetics from the previous chapter shows us that almost all beneficial individual mutations will be lost.

tess:

Glad you enjoy it!  This is when things start getting interesting.

Daniel:

An obsidian/titanium ring would be beautiful!

Neal:

As the series continues and wraps up, I'll present what I believe to be the most likely timing for the scavenging/hunting transition.  There's actually some good evidence for it...and while nothing is certain, I believe one "most parsimonious explanation" stands out.

JS

Fmgd:

Now that the evidence is much less sparse, I won't have to go into so many individual fossil examples!

And I understand what the drama is about, but I feel no need to participate in it or contribute to it.  There's plenty of science to explore.

Leslie:

The examples of modern hunter-gatherers should be more than sufficient to disabuse people of that notion.  African Bushmen are perfectly capable of taking down elephants without guns...in fact, the bigger and slower the animal, the easier it would have been for our ancestors to kill.  But we'll get into that discussion later.

It's instructive to remember that intelligence must be for something or it never would have arisen!  In other words, intelligence must have had survival value...

...and that is the reason this series exists.  If we didn't need intelligence to survive, we never would have become intelligent!  Therefore, it's important to figure out what intelligence is for.  

I'm glad Gryka's story resonated with you.

Txomin:

We'll never know the exact thought process that led to tool-making.  However, we must keep in mind that it had to have been very difficult for our small-brained ancestors, and understandable only to the smartest few -- otherwise they would have come up with it long before!  

Here's an analogy: a physical simulation of a motorcycle wheel on smooth pavement involves no less than the solution to five simultaneous linear equations.  (And this is a simplified model: a realistic model involves more.)  The percentage of humans who can comprehend the physics and mathematics required to understand that simulation is extremely low...let alone the percentage who could envision and write it in the first place!

Inventing and comprehending stone tool manufacture with a 400cc brain would have been a similar problem.  Only the smartest australopithecines would have been able to make the connection.  

With the benefit of hindsight, a brain over 3x as large, and thousands of years of cultural knowledge, it's easy to say how we would have solved the problem...but that doesn't tell us anything about how our ancestors did it.

JS