Myth: The number of people currently living is greater than the number of people who have ever died.
This claim seems possible, if unlikely, especially because it supports popular notions of world overpopulation that became popular in the 1970s and have been circulating, more or less, ever since. However, there are two methods of scientific thinking that can be used to determine the validity of this claim.
The first applicable principle is that of falsifiability. This is something of an issue in this situation because it is impossible for us to know exactly how many people have died in the past - we can estimate population size going back to the time of the first modern human skeletons that have been found, but we can't be positive that there weren't earlier individuals that we haven't found evidence of. Still, let's assume our estimates are close enough to use for these purposes.
The biggest problem with this claim is based in the principle of extraordinary claims. Essentially, extraordinary claims, such as this one, would require extraordinary evidence in their favor in order to be considered sufficiently supported. Thus, even though we don't know for sure that there aren't more dead people than we can be aware of, we would need to have reason to believe that there were considerably fewer than there are people currently living in order to accept such an extraordinary claim. Because our estimates actually suggest that there are considerably more people that have died in the history of the world than there are currently living (between 12 and 110 billion being the widest range, with consensus tending around 60 billion as opposed to nearly 7 billion living today), there is hardly any evidence to support this claim, let alone enough to support such an extraordinary claim.