As my nod-off-book, I'm reading (again) Stephen Pinker's "How the Mind Works". It really is an excellent book. Just before I nodded off last night I was reading the speculations about the date of the earliest traces of homo sapiens sapiens, i.e. us.
Pinker talks about the date possibly being around 45,000 years ago.
Now, I don't know about you but I find numbers from around that big and upwards hard to digest. I think we tend to be comfortable with tens and hundreds but when you get into thousands, never mind millions and billions, we lose the arithmetical perspective.
This is perhaps why politicians can say, "the plans we have for reforming XXX will cost 5 or 6 billion pounds/euros/dollars..." and no-one says in return, "hang on a mo, pal... that is a difference of 1 bleeding BILLION! What kind of accountants do you have there?"
Anyhow, I put down the book, turned off the light and started thinking about making all this a bit more graphic.
How about imagining you are on a path, let's say a long country path in the autumn sun... so not too hot, pleasant and fresh... the leaves on the trees are just beginning to turn from green to a slight yellowy-brown... late wasps are buzzing drunkenly...
So... erm.. oh yeah - we are on a path, and now imagine that one step you take is the equivalent of going back 2000 years into the past. So with one step along the path you cover all of recent history back to the clock change from B.C to A.D.
Ok, one step and we are back 2000 years to about year zero. Then take another step and we have reached the first known written texts, the beginning of writing. Every book/papyrus roll/clay tablet/etc. that has ever been written in human history for people like me to nod off to is covered by those two steps.
Take 4 more steps, so 6 altogether so far, and we have arrived at the moment some people somewhere grew a bit of wheat and put a fence around it. The start of agriculture.
To get back to Pinker's date for the possible emergence of us as a species of tool-using, hunter-gathering, foraging creatures you need another 18 steps (please feel free to check my maths!).
So, 24 steps in all to get back to the very first humans who were like us. We wouldn't even need a sit down. Then to get to the oldest distinctly human fossils you need about 80 paces.
Ok, this is fun! Where to next? How about everyone's favourite - the dinosaurs. Let's stroll to the "end of the dinosaurs"; the massive meteor collision which wiped out all the tyrannosauri and brontosauri and whatever and left the coast clear for our very early mammalian ancestors.
How many steps do you think? 100? 500? 1000??
Have a guess, I'll tell you later!!