Pondering about Life and Death.

By now, our world population has reached around seven billion Human earth dwellers; a stunning figure. Since the world poplulation is still growing, we might presume, we are doing all right. Because a growing population means, there are more newly born inhabitants then there are perishing. This overabundance of birth is a result of what we call a succesfull species; and no matter how vulnarable we are - as a species - we still manage to get older. Over our existance, our life expectancy has doubled, and so did our birth rate; of course, these are rough estimations.
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To me, this raises all kinds of questions, like: "How many people were born, and how many died, over our time?" This is simple calculus, one might say: "People born, minus people died, equals 7 billion". That's the easy part. And if we knew the exact birth- and death-rates - on average, over time -  we could easily work this out. But of course, we do not know that properties; we have no statistics on that. Nowadays, births and deaths are recorded, but that has not always been the case. So we have to make an educated guess.
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We know one thing for certain: a person has to be born to count, and then it has to die. How long this - his life - will take, is uncertain. On average, our lifespan is 70 years, worldwide nowadays. We can figure out, by studying remains of very old dead people, what was the life expectancy back then. But how often a new baby was born - worldwide - is a statistic mystery. Also the many wars, humanity suffered, throw a cloud over our life expectancy. Nonetheless, I will give it a shot.
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Let us assume a birth rate of 1 new person per second, in modern times - this is not an exaggeration; we assume a birth rate of 1 per 4 seconds (why? one has to start at some point) at the start of our timeline. We assume a lineair function of birth rate over time (why? ...). Our timeline starts 10,000 years ago, the rising of Homo Sapiens (why? ...). We will not bother ourselves with death-rates, because they are unpredictable. They will be the remainder of our equation... Let's go...
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In the first 2500 years, in seconds, 78,840,000,000 / 4 = 19,710,000,000 were born...
In the second lap, 78,840,000,000 / 3 = 26,280,000,000 were born...
In the third lap, 78,840,000,000 / 2 = 39,420,000,000 were born... 
In the fourth, 78,840,000,000 / 1 = 78,840,000,000 were born... 
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Grand total: over 10,000 years, we reach a possible figure of 164,250,000,000 births, roughly... Luckily, most of them died by now; we have 7 billion left, out of 164, and a quarter...
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But were did all the dead people go?
That must be a very crowded place...