Blaffer Hrdy estimates that cooperative upbringing began

at the beginning of the Pleistocene epoch (about 1.8 million years ago) when the African Homo erectus appeared. The author drew this conclusion from the relatively small difference in size between the sexes compared to the much older Australopithecines.

The male Homo erectus were

only 18 percent larger than the females. This degree of sexual dimorphism is only slightly more pronounced than in modern humans. (p. 384)

The plausible interpretation of Blaffer Hrdy would mean that the hominids were looking after their young together long before Homo sapiens. Therefore, the use of human communication by the helpers and thus the whole group of Homo sapiens is very plausible.

Carel van Schaik and Karin Isler also emphasise the importance of the helpers in caring for the young:

In most mammal species, the mother is on her own during the strenuous gestation and nursing periods, so any help will save the mother energy.

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Explanation:

No mammal on Earth has produced young that take longer to mature or depend on the support of so many others than Pleistocene humans.

With the help of alloparents and parents, these offspring – incredibly costly and equipped with large brains – slowly grew up and enough survived to produce a population capable of penetrating into new habitats, raising children there, spreading further, and eventually populating the entire planet.

Nourished not only by their mothers but also by other members of the group, even descendants who were weaned long before they could care for themselves could slowly grow up without suffering hunger.
(German: Sarah Blaffer Hrdy 2010: Mütter und andere, Berlin, p. 377)

Because of the longer childhood and adolescence, the raising of the young has become extremely expensive for humans and their forerunners. Sarah Blaffer Hrdy, the originator of the quote, has dealt with the prolonged course of human life and its consequences.

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