The answer is based on some calculations which were published by the International Statistical Institute.
If the world population had always been increasing at its present rate, doubling within an average human lifespan, then the living would indeed outnumber the dead.
However, this is not what has happened.
There have been very long periods in the past when the population hardly grew at all, but when deaths continued to accumulate.
For historical periods, there is a surprising amount of information on population figures, including censuses conducted by both the Romans and the Chinese.
Before then, there are estimates based on the area of the world which was under cultivation or used for hunting, and of the numbers of people who could be supported per acre using these methods of food production. According to estimates assembled by J.-N. Biraben, the world population was about 500,000 in 40000 BC.
It grew, but not at a steady rate, to between 200 and 300 million in the first millennium AD, and reached 1 billion early in the 19th century.
On multiplying the population numbers by the estimated death rates, you discover that the total number of deaths between 40000 BC and the present comes to something in the order of 60 billion. The present world population is still only about 6 billion.
Although no great claim can be made for the accuracy of the historical estimates, the errors can hardly be so large as to effect the conclusion that the living are far outnumbered by the dead. This has always been the case, and will continue to be so into the indefinite future.
In the Garden of Eden, the living outnumbered the dead.
In the Indian epic poem Mahabharata the eldest Pandava, Yudisthira, was asked many questions, including the one posed above, by the god Yama, who was the keeper of the Underworld and all that is righteous, to test Yudisthira’s knowledge, power of reasoning and truthfulness.
Yama was disguised as a stork guarding a pond from which Yudisthira’s four brothers drank without being able to answer a single question and were all struck dead.
The stork Yama asked “Who are the more numerous, the living or the dead?” Yudisthira answered: “The living, because the dead are no more!”
Yama accepted this and all the other answers given by Yudisthira and, with great pleasure because Yudisthira was actually the son of Yama, blessed him and revived all of his dead brothers.