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Re: Multi-age Broods. Ignorance or Apathy?
John Waters (jdwaters@dircon.co.uk)
Tue, 13 Aug 1996 03:28:05 +0100
Wallace Neslund wrote:
>
> John Waters wrote:
> > In fact, the human
> > specie is the only mammal to rear multi-age broods to maturity. Apes by
> > contrast, have single age broods.
>
> This is not so. Pan females have non-adult children of different ages, both
> breast feeding infants and adolescents.
JW: The statement concerning Pan females is potentially confusing. Pan
Females do not have breast feeding infants of different ages. They may
have a pair of breastfeeding infants of the same age. Older infants may
associate with their parents in a family group, but such infants are not
in their preweaning stage of development.
Clearly, definitions are important here. My definition of weaning is the
process whereby infants become independent of their parents in repect of
the provision of food, transport and protection. If an infant is
dependent upon a parent for food, it is in its preweaning stage of
development.
>
> > A multi-age brood is defined as a brood of mammal young, of different
> > ages, all of whom are in their preweaning stage of development. The age
> > difference must be at least one gestation period.
>
> Pre-weaning by definition means they are still living on breast milk and have
> not switched to solid food.
JW: Preweaning should not be confused with breastfeeding. All mammals
breastfeed by definition. Many mammals have an intermediary stage
whereby they gradually transfer from breastfeeding to solid food. The
mammal young are considered weaned when they are no longer fed by the
adults.
>
> > Apes generally rear one infant at a time. They can give birth to twins,
> > but these do not generally survive in the wild, due to feeding and
> > transportation problems. As a 'norm', apes wean off their previous born
> > infant at least three months before the next infant is born. The average
> > birth interval for chimpanzee infants born in the wild is five and a
> > half years.
>
> The Pan female does not breast feed her young for five and a half years!
JW: Correct. The Pan female normally breastfeeds her young for about 3.5
years. However, the birth interval of chimpanzees in the wild is still
five and a half years. This is due to infant mortality etc.
Ref: Short. R.V., The evolution of human reproduction. Pro. R. Soc.,
Ser. B. 195. p. 3 - 24 (1976)
>
> > By contrast, in modern industrial societies, human mothers may give
> > birth every year. As the age of weaning for a human infant is about
> > seven years of age, a human mother can concurrently rear six infants at
> > once.
>
> The average age for weaning is not seven years in Hss. Most Hss infants can
> eat pre-chewed food at a year. They can, and most do, live entirely on solid
> food by age three. The average age for weaning in Hss is one to three years,
> depending more on culture and society than on physical need. Weaning is also
> further modified by the use of bottle fed babies. Breast feeding has some
> amount of inhibitor effect on the mother's getting pregnant again. If a Hss
> baby is bottle fed instead of breast fed, the mother can get pregnant
> relativly soon after giving birth. This inhibitor effect is not an absolute
> constant, though, and a breast feeding mother can sometimes still get
> pregnant. I do not know if any studies have been done on Pan mothers with
> bottle fed babies, but this same inhibitor trend may apply to Pan as well as
> Hss.
> JW: Definitions again. The inhibitor effect is due to the level of
prolactin in the bloodstream. It is not breastfeeding per se which
prevents a return to estrus; rather it is breastfeeding upon demand. The
post weaning age of Hss is the age at which the infant is capable of
independence, without any post weaning psychological traumas which would
prevent the development of a normal adult. In hunter-gather tribes, this
is generally six to seven years.
> > It is curious that this multi-age brood characteristic is not mentioned
> > in any encyclopedia, or any reference work on primates. Is this due to
> > ignorance or apathy?
> >
> > John Waters
>
> The fact is that your definition of multi-age brood is not consistant.
> Neither Hss nor Pan usually have a second birth while still breast feeding
> the first infant. Both Hss and Pan, though, do have multi-age brood that are
> still sub-adult and to some extent dependant on their mother for support and
> protection, but only the youngest is still breast feeding. The older children
> in Pan, are, to the most extent, self feeding. In Hss, the older children,
> with a much more drawn out childhood, are being fed pre-chewed or soft food,
> but are no longer breast feeding. If a Hss mother had a child every year for
> three years, or even a theoretical five children in three years (ages 0, 9
> months, 18 months, 27 months, 36 months) she would have trouble keeping all
> of them fed with breast milk alone. By necessity, the older child would be
> weaned when the next one is born. The inhibitor effect of nursing tends to
> postpone prgenancy until the first child is weaned. There is also the
> question of estrus to consider. Most mammals will not enter estrus while
> still nursing infants. This is true of Pan and other primates. Hss, though,
> has no seasonal estrus cycle, replaced instead by a monthly cycle of
> fertility. If the only normal prohibitor of pregnancy in Hss is due to
> nursing, then the use of bottle fed babies will disturb this cycle and allow
> for multi-age broods by your definition. This must be viewed as a social
> abberation to an organic cycle, though, rather than as a normal state. There
> are other natural prohibitors of pregnancy, such as starvation and very
> extreme physical labor, but those are survival trends for extreme situations
> and are not pertinent to this post.
JW: A detailed answer deserves a detailed response. Both Hss and Pan can
have a second birth while still breastfeeding the previous born infant.
In Pan, this is rare. When it happens, the previous born infant is
immediately weaned off. In Hss, structured breastfeeding - i.e. feeding
at set intervals throughout the day, allows the female to come into
estrus and be remated. However, the previous born infant is normally
switched to bottle feeding to allow the colostrum levels to build up for
tne next baby.
>The older children
> in Pan, are, to the most extent, self feeding.
JW: Nearly correct. The previous born infants are completely
self-feeding.
>Most mammals will not enter estrus while
> still nursing infants. This is true of Pan and other primates. Hss, though,
> has no seasonal estrus cycle, replaced instead by a monthly cycle of
> fertility.
JW: The sexual physiology of Pan and Hss is not all that different. They
both have monthly cycles, and neither are seasonal in terms of estrus.
This is due to an adaption to equatorial environments.
> Wally
> Thanks Wally,
John
> God knows, I don't. - Thomas Aquinas
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