Re: LBI Broods and Social Sharing

A R Millard (A.R.Millard@durham.ac.uk)
4 Oct 1996 08:34:09 GMT

John Waters (jdwaters@dircon.co.uk) wrote:
: Can anybody help me to determine the time and place where the
: hominid LBI Brood and Social Sharing first developed?

OK, lets try first to put some limits on it from the archaeological
and palaeoanthropological evidence.

: ......... Social Sharing is a behavioural trait
: whereby adults of a mammal specie voluntarily share food with
: other adults.

Earliest evidence: the male Neanderthal Shanidar 1, had deformities which
would have left him unable to forage for himself, and yet he survived
several years following his injuries (Gamble & Stringer 'In Search of the
Neanderthals' p94). Social sharing must have occurred amongst
Neanderthals. Given that social sharing is thus a common caharacteristic
of modern humans and Neanderthals, it is likely to have been present in
their common ancestor - (later) homo erectus.

: The multi-age brood characteristic developed as a result of the
: increasing period of hominid infantile helplessness after birth.

: ........ it is generally held that the human baby€s foetal stage
: of development extends beyond its gestation period.

Which we link to the necessity to be born when the head can still be
fitted through the birth canal of a bipedal mother. Thus multi-age
broods and LBI probably arise with or after bipedalism, i.e. in A.
Afarensis or later.

: It was the increase in the hominid infantile stage which led to
: the development of the LBI brood characteristic. At some point
: in time, the hominid mother gave birth to a new baby, while her
: previous born infant was still in its infantile stage. The
: mother concerned may have been overindulgent, perhaps even
: abnormal. But if there was a
: super abundance of food, she would be able to feed the previous
: born infant on adult foods, while breastfeeding her new-born
: baby.
I imagine this to have happened gradually: as gestation shortened to
accommodate larger heads, so the feeding of infant A had to overlap more
and more with that of infant B, and once the ape-like cycle of stopping
feeding infant A when infant B arrrives had been broken, then social
sharing might develop as you describe.

There must also be a birth interval with maximum evolutionary benefit,
playing off the benefit of a larger number of offspring against the
survival rate when having to feed more than one infant at a time.

: If it is any help, it can be shown that the advent of social
: sharing would lead to a substantial increase in the rate of
: evolution. Furthermore, it can be demonstrated that the LBI
: multi-age brood would lead directly to the evolution of human
: speech and language. Any ideas anyone?

Do you mean that they necessarily lead to speech and language or that the
enable its development. Evidence for language occurs later than the
evidence for social sharing (excepting the latest dates from Australia,
until we see the full evidence in Antiquity).

So I haven't whittled down the timing much but it is clearly between A.
afarensis and H. erectus.

Andrew Millard