Jeremy M. DeSilva with the Department of Anthropology at Boston University published research that demonstrates early hominids exhibited shared parenting and "modern" birthing behaviors much earlier than previously thought. This discovery leads to a conclusion that "modern" parenting behaviors developed much earlier than previously thought.
The research was published on line at the PNAS web site on January 3, 2010, Abstract is available at this site.
DeSilva compared the ratio of baby weight to mother’s weight in present day humans from all parts of the world, living apes, chimpanzees from several parts of the world, and gorillas. A similar comparison was made with the remains of Homo erectus, Homo Sapiens neanderthalensis, and Australopithecus.
The results led DeSilva to conclude that early human ancestors had a very similar baby to mother weight ratio to present day humans.
That fact combined with a structured estimate of early human’s height and weight based on literature combined with an examination of existing remains led to the following conclusions:
Females of the Australopithecus species were transporting proportionately large infants,
The costs of carrying an infant (approximately 16 percent increase) may have also reduced the amount of traveling done by female Australopithecus,
In Australopithecus, birth may still have been a challenging physiological event, perhaps requiring the assistance of helpers, especially if shoulder rotation during asynclitic birth occasionally caused occiput anterior orientation of the newborn head.
Paper
A shift toward birthing relatively large infants early in human evolution
