Will the number of cumulative dead humans, say since 30,000 BC (or pick your own “reasonable” starting year for human existence), over take the number of living humans? If yes, when?
If you mean the number of people who ever lived (and are now dead) versus the number of people currently living then I would have thought the former overtook the latter a LONG time ago!
This has been addressed by Cecil and he gives the answer of 33 billion to 74 billion since about 25,000 years ago.
A better question would be “when did this happen?”, since there are currently about 6 billion people alive, and estimates on the number of humans who have ever lived range anywhere between 60 and 120 billion.
Dang scooped again!!
I saw your post right below mine. And then I checked again and Q.E.D.'s post had snook in there!
Confused hamsters?
It’s incredible to comprehend that there was upwards of 126 billion human members, living and dead, on this Earth and yet less than only 5%, before adjusting for those reincarnated, are still alive!
For me it’s incredible to comprehend that the estimate is only between 60 and 120 billion. I would have thought it was more.
Quite an impressive sight, I presume.
I’m with dakravel. For me that statistic is incredible the other way - out of all human history, one-twentieth of the people that ever lived are still alive today? I’m pretty sceptical.
All that tread
The globe are but a handful to the tribes
That slumber in its bosom.
—William Cullen Bryant, “Thanatopsis”
Really? We’re only talking about 120,000 years here, you know.
I heard it was one fifth, so the answer is less than I thought. Not sure where that one fifth figure came from. Maybe it was considering a much shorter timeframe, because as Cecil pointed out it depends on what you call human.
Unless my thinking is way off, wouldn’t it have been very early in the game, certainly within the first 100 years of human existence?
Life expentancy at birth was very short until comparatively recently. If we arbitrarily call the beginning of human existence year H (be it 30,000BC, 25,000 BC, or whatever), all of those now-defined-as-human infants dying young after year H are immediately members of the “Dead Team”. Within a very few generations, probably three at most, there will be more on the “Dead team” than on the “Living Team” unless you postulate a huge increase in birthrate from one generation to the next, which would seem unlikely. ISTM that by the year H+100 the Deads would be ahead in numbers for good under any reasonable scenario, and once they’re ahead they never look back.
The above rationale assumes humans evolved from a population of some protohuman around year H. Of course, if you believe that it all started with just two humans in the Garden of Eden, and that many of the early patriarchs lived hundreds of years, the above numbers get skewed somewhat. 
It’s not reasonable to say that once the number of dead exceeds the number of living that it’s ahead “for good.” Look at a historical graph of the world’s population, and you’ll see that you’ve roughly got an exponential curve. Exponential indicates that the rate of increase is continuously increasing.
So, for the last few hundred years, the birth rate has exceeded the death rate by large margin. It’s been enough to make the world’s population double fairly quickly (right now, it’s something like every 30 years or so).
My guess is that the real scenario is more like this (these are notional numbers): 500 years ago, the people who were alive made up, say, 1% of the people who ever lived. The population of the Earth was much closer to the level in the thousands of years previously than current level. Such is the nature of an exponential curve.
Today, if we believe the above posts, the number is about 5%. There are more dead people now then there were 500 years ago, but there are way more living people.
It’s reasonable to assume that if we were to have unchecked exponential population growth, that the number of living people would eventually reach 50% of the number of people who have ever lived. That probably isn’t possible in reality. But it’s mathematically doable, and invalidates your above assumption.
If population growth were linear, there would be no way for the living to ever catch up once they were behind.
HIJACK: A couple of things to point out that don’t relate to the main point (dead versus the living) but do deal with exponential population growth. “The world’s population history is an example of exponential growth” is one of those truisms that is repeated in virtually every math or statistics textbook, but in point of fact historical demographers today know it’s not really correct.
First, yes, it is true that if you plot out reasonable estimates of world population you can very easily fit an exponential curve to the data. But by far the biggest reason why this works is the massive population growth of the last two hundred years: it absolutely swamps everything that came before. If you omit the last two hundred years, the situation is far less clear.
For example, take a look at this:
http://www.ined.fr/englishversion/publications/pop_et_soc/pesa394.pdf
Ignore the first graph in the article: it’s mostly speculation about time periods for which we have no data. Instead, look at the second graph: it’s for China, which has the best historical population data in the world.
While the graph has some wild wobbles in it, you could still fit an exponential curve to it pretty easily. But now do this: use your right hand to cover up the all data after 1800. Now look at the graph again. It doesn’t look like expenential growth any more, does it? In fact, it looks more like linear growth (with, again, some huge wobbles in it.) So while the last 200 years may have seen exponential growth, it’s not clear that periods before that did.
Second, even though demographers often use exponential population growth models, they know from their research on the last 200 years of data that the exponent involved is not constant–i.e. population accelerates not at a constant rate, but a variable one. Indeed, at the moment the exponent is falling, i.e. the population growth rate is decelerating. Many demograpers expect that 100 years from now we’ll be seeing a falling world population.
Third, population estimates for before the rise of the Roman and Chinese empires are almost entirely guesswork (and are sometimes merely backwards projection using simple exponential growth models.)
Mind you, this doesn’t impinge on the dead vs. living thing–again, population growth for the last 200 years has been so explosive that it probably won’t do much damage to treat the data as if it showed exponential growth for the purposes of that question.
But it’s vitally important to understand that the world population isn’t locked into constant exponential growth: again, demographers expect the world population growth rate to slow dramatically or even become negative over the next century.
Yeah, and that’s why I said “roughly.”
And then again, if you look at the part of a true exponential curve far to the left of the elbow, it is hard to tell from linear. So either description of the behavior is equally inaccurate.
That is exactly what I would expect if you take a constant-growth-rate curve and cover up the steepest part. The graph is scaled to show the most recent, high values, and this scaling is such as to create an illusion of slower growth in earlier periods.
An excellent resource for those interested in these matters is called Atlas of World Population History by Colin McEvedy and Richard Jones. My copy is a paperback edition from 1978 - I don’t know whether it is still in print. For each country extant in 1978, the authors provide a graph and an article describing the population through time, drawing on a very wide variety of disciplines to estimate historic data.
Actually, if you assume exponential population growth and constant human lifespan, then the ratio of dead to living will be constant forever. Only by increasing the human lifespan or decreasing the characteristic time of the exponential could you change the ratio, and even then, once you changed the timescales, the living:dead ratio would still asymptotically approach some new value.
The vast imbalance between the dead and living suggests that either human population growth is not well modeled as an exponential, or that the characteristic time of the growth is much longer than its potential value.
Well, the doubleing rate has gotten smaller and smaller over the last few hundred years. So the rate of growth has been even more accelerated than an exponential function.
This seems to mesh well with the fact that the average human lifespan keeps getting longer.