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VIEWS: 3 PAGES: 81

									                          Primate
                            life

                           Shares a general
                         developmental pattern
                          with other mammals
A period of dependence
                                 Primate
                                   life

                                  Shares a general
                                developmental pattern
                                 with other mammals
Pre-reproductive independence
             Primate
               life

              Shares a general
            developmental pattern
             with other mammals

Adulthood
                             Primate
                               life

                              Shares a general
                            developmental pattern
                             with other mammals

Then something happens...
And we are
 primates
   too...
               very rapid
              growth, but
              rate falling
                  fast


                                                 sudden rapid
                         slower,                    growth
                          even                    again, then
                         growth                   rapid fall in
                                                      rate


                                   growth rate
                                      drops                       growth
                                                                   stops




But development is not just marking time -- there are PATTERNS to
                   growth. What’s up with that?
             INFANT



                                           ADOLESCENT
                   CHILD


                          JUVENILE
                                                        ADULT




But development is not just marking time -- there are PATTERNS to
                   growth. What’s up with that?
                        Bogin says that nonhuman primates don’t have
                       growth spurts; they DO (in weight, if not height).
Many primates share   But what does height mean to a quadruped, anyhow?
this pattern of
growing FAST in
utero [not shown],
then slowing down
for a while, and
finally showing a
growth spurt just
before adulthood.

 Adolescent
growth spurt
Duration of adolescent growth spurt in primates
                                                       Each point
                                                  represents male (o)
                                      male
                                                   or female (∆) of a
                                    men
                                                   different primate
                                    women
                                                        species.
                           female




                                                  Our growth spurts
                                                   last about as long
                                                  as expected for our
                                                       body size.

From Leigh 1996: Fig. 12
                           What is odd
                              about
                            humans is
                             NOT the
                          length of our
                             growth
                           spurts, but
                          how late they
                              start.
From Leigh 1996: Fig 13
The way to get a late start to
the adolescent growth spurt
         HERE ...
                     The way to get a late start to
                     the adolescent growth spurt
                                HERE
              ... is to turn
               growth off
                  HERE




Why do humans turn growth off? Is there a reason????
   LIFE HISTORY THEORY
      “…natural selection favors organismic life cycles in
      which resources are allocated among growth,
      maintenance and reproduction in relation to age or
      size in a manner that maximizes the reproductive
      potential across individual life spans.”
      Pereira 1993: 17


                                                             M = lifespan

Basic life histories can be                                  a = maturity
compared across Orders. For
example, on average Primates
mature later and live longer
than other mammals.
Life histories can also be studied
at the level of individuals--after
 all, it is individuals which have
                 lives.
   The kidney fat index is the ratio
between fattiness of mother’s kidney &
   her calf’s. Since all the calf’s fat
 comes FROM mother, a high value
                    of
             calf:mother
  is a sign of greater investment
             by mother.
   Why should older mothers invest more?
Does the life-history perspective MATTER?

If we as a society want to promote learning more than
one language, when should our schools first offer such
training?
  A) Elementary school
  B) High school
  C) College


WHY?
Today, ask 4 questions:
1) why do primates in general extend the
     immature period?
2) why do humans take this to such an extreme?
3) how does this extreme extension of
     immaturity (right up through your last date,
     at least) relate to understanding what
     modern humans are all about?
4) how might our development pattern have
     contributed to the evolution of language?
Why do primates in general extend the immature period?

                                                    M = lifespan
                                                  a = sexual maturity




   Age at sexual maturity and total lifespan are both greater (for a
     given body weight) in primates. Long life seems nice, BUT...
Being immature longer has a reproductive COST !!

Evolutionary theory predicts there must be a
    benefit that is greater than that cost.
Primates tend to live in
groups. This has a lot
of advantages… but
means young sometimes
are competing with
adults for food.
NOT a good idea...
                        Primates tend to live in
                        groups. This has a lot
                        of advantages… but
                        means young sometimes
                        are competing with
                        adults for food.
                        NOT a good idea...
So, why do primates in general extend the
           immature period?
 To grow faster would increase competition
 for food with non-parent adults --
 competition that the young would usually
 LOSE. Loose too often, you starve to death.
                   This idea -- that extended
                   immaturity is a way of
                   avoiding competition from
                   adults -- reminds us that while
                   parents have a strong reason
                   to help their offspring, many
                   others DON’T.




And this helps to explain two puzzles
         introduced earlier.
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 Asked what height
 means. ALSO, note
 that in all the great
 apes, the spurt is
 more dramatic for
 males -- why?

 Good reason to think
 these are connected.

   Adolescent
  growth spurt
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 When quadrupeds
 fight, they typically
 use their teeth --
 after all, hands have
 to be adapted for
 walking.
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 When quadrupeds
 fight, they typically
 use their teeth --
 after all, hands have
 to be adapted for
 walking.

  Chimpanzees
  have big canines,
  but they also hit.
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 And they can do it
 pretty effectively.

 Notice the use of
 height to both look
 more intimidating
 and provide more
 force for a blow.
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 And they can do it
 pretty effectively.

 Notice the use of
 height to both look
 more intimidating
 and provide more
 force for a blow.

    I hope you saw where
       this was going...
Back to an earlier question:   What does height mean to a
                                 quadruped, anyhow?
 It is very plausible
 (though hard to
 prove) that we have a
 {male} growth spurt
 in height, while great
 apes (at least) do in
 weight, because those
 are the variables
 important in fighting
 (with adults).
 II. Why do humans
 take this to such an
      extreme?
  More than you wanted to know
    about human evolution.

Key points:
1) the line leading to us
  shared an ancestor with the
  line leading to chimpanzees
  about 5-7 million years
  ago.
 II. Why do humans
 take this to such an
      extreme?
   More than you wanted to know
     about human evolution.

Key points:
1) the line leading to us
  shared an ancestor with the
  line leading to chimpanzees
  about 5-7 million years
  ago.
2) the first thing to distinguish
  us was bipedalism.
 II. Why do humans
 take this to such an
      extreme?
   More than you wanted to know
     about human evolution.

Key points:
1) the line leading to us
  shared an ancestor with the
  line leading to chimpanzees
  about 5-7 million years
  ago.
2) the first thing to distinguish
  us was bipedalism.
3) LATER, our brains began
  expanding.
           Bipedalism represents a
           major change in posture,
           which creates a problem not
           usually faced by
           quadrupeds:




Tipping over.
Three ways to solve this problem are:
1) Move the pillars underneath the center of gravity by
       a: angling the legs inward
       b: narrowing the hips (blue arrows)
2) Use big abductor muscles to stabilize the hip (gluteus maximus - your butt)
                                     Australopithecus


                                                        We did all three.




    Chimpanzee                           Human
                 (pelves not to scale)

We brought the hipjoints closer to the center of
gravity, made it [relatively] narrower, and flared
out the bones to (a) make attachments for the
gluteus muscles, and (b) make a cup to hold the
guts.
     Hominid brain size evolution:
                                                Modern
                                                range




                                             African apes




We were fully bipedal by 4 million years ago. A bit
later, our brains started swelling... this is one way
to look at it. But if you read Leigh’s article, ...
... you know there’s another - allometric analysis.
There was a large, fast increase in body size with
Homo erectus. In this view, brain size has two
steplike increases, at ≈ 2mya and ≈ 0.5mya.
               The “obstetric dilemma”
                     (chimpanzee)                        (modern human)
                                    (Australopithecus)


Blue arrows
indicate
direction
baby facing;
mother’s
stomach is
facing             As the fetus begins to descend, there                  Note that
upwards.                                                                  human infant
                   is plenty of room for the chimpanzee
                                                                          has to twist,
                   (facing forward); hominids have to                     and then face
                                                                          toward
                   face sideways but there is room.
                                                                          mother’s back.



   What does that pelvic narrowing & brain expanding do for giving
                            birth? Ouch.
                The “obstetric dilemma”
                      (chimpanzee)                        (modern human)
                                     (Australopithecus)


Blue arrows
indicate
direction
baby facing;
mother’s
stomach is
facing                                                                     Note that
upwards.                                                                   human infant
                                                                           has to twist,
               At the halfway point, chimp is still OK.                    and then face
               Australopithecus manages shoulders with                     toward
               small bend of neck, but human has to rotate to              mother’s back.
               facing backwards.
   What does that pelvic narrowing & brain expanding do for giving
                            birth? Ouch.
               The “obstetric dilemma”
                     (chimpanzee)                        (modern human)
                                    (Australopithecus)


Blue arrows
indicate
direction
baby facing;
mother’s
stomach is
facing                                                                    Note that
upwards.                                                                  human infant
                                                                          has to twist,
                                                                          and then face
                                                                          toward
                                                                          mother’s back.



   What does that pelvic narrowing & brain expanding do for giving
                            birth? Ouch.
We “solved”
bipedalism, but
the solution seems
to put a limit on
brain size. That’s
not good, since for
some reason we
seem to need big
brains...
  What to do???
     Give birth “earlier” in development, and let
      the brain do some of its growing outside.
                                 Nonhuman primate brain
                                 growth pattern is fairly
         Birth                   consistent: fast growth in utero,
                                 then slowing after birth.
                 Rhesus monkey




Human pattern looks the same,
but fast growth doesn’t start to                    1 year old

taper off until > 3 months old.
We are born premature.                      Birth            Human
 Modern human infants are born with relatively
 less-developed (and smaller) brains than other
                   primates.
Because of this, we are altricial - helpless at birth. A
(relatively) precocial infant chimpanzee can hang onto
her mother within about a day of birth.

Importantly, this means that a bigger proportion of
our neural development is taking place outside the
uterus. Infants are receiving vastly more stimulation
at early developmental stages than is true for other
primates.
 Modern human infants are born with relatively
 less-developed (and smaller) brains than other
                   primates.
Because of this, we are altricial - helpless at birth. A
(relatively) precocial infant chimpanzee can hang onto
her mother within about a day of birth.

So humans are growing slow (like other primates),
AND “starting earlier” so that there is more growing
to do.

     Do we know when that pattern started?
                                Estimating age at
                                death from teeth:
                                Permanent teeth erupt at different ages
                                in apes & humans:
                                         Chimpanzee          Human
                                1st molar    3.3               6
                                1st incisor     6                6.5
                               Well-worn molar with new
                               incisor: development similar
                               to chimpanzee (fast). Same
                               wear on both: human pattern
                               of development (slower).
     Australopithecine teeth

Australopithecus developed fast, like chimpanzees.
                                    So that’s how
                                    becoming bipedal
                                    changed the nature
                                    of infancy and
                                    promoted evolution
                                    of larger brains ...
                                    But is that long
                                      childhood
                                      purely an
                                     unavoidable
                                        cost??


And while we’re at it, can we shed light on
           grandparents too?
    Juveniles & children can help produce more
children, by helping with those ‘premature’ babies.
   Why
menopause?
Grandparents
(grandmothers
especially) can also
help directly,




                       as well as indirectly
                       through their
                       knowledge and
                       wisdom.
             Though both
             human and
             chimpanzee
             females stop
             reproducing
Chimpanzee   by age 50, we
             just keep on
             going...
The result of this helping by
both “ends” is that humans
can have shorter interbirth
intervals (IBIs) than apes.
And the result of that is that
even though we grow slower,
we reproduce faster.
Today there are about
6,177,792,718 humans, and
fewer than 150,000
chimpanzees.
III. How does this extreme
extension of immaturity
relate to understanding
what modern humans are
all about?


At some point, we get into
positive feedback:
 Ability to learn, +
 Opportunity to learn
results in payoffs to learning,
and favoring larger brains with
which to do it.
IV. With all this learning going on, where did language
     come into the picture?
      Many animals communicate well without “language”.
      Why was this ability favored in us, and no other
      primate? *
      One theory (there are others) looks at something
      we’ve already talked about, with a twist.




                                 * Washoe, Kanzi, Koko, Chantek
                                 and other apes can learn to use
                                 parts of human language, but at
                                 nothing like adult human levels.
  IV. With all this learning going on, where did language
       come into the picture?
        Many animals communicate well without “language”.
        Why was this ability favored in us, and no other
        primate? *
        One theory (there are others) looks at something
        we’ve already talked about, with a twist.


Infant chimpanzees can
hold on to mother from the
first day, and this frees up
mom to do whatever needs
to be done...
            Human infants need to be carried,
            which is not always convenient.




Sometimes, mother has
to put the kid down
while she does
something else ...
What if they get separated?
Mammals that don’t den either carry
their infants, or the precocial infants
follow mom.
The problem of coordinating behavior
over a distance just doesn’t come up.
Hence the need for elaborated mother-infant
communication. According to biological anthropologist
Dean Falk, the first sentence was probably something like

         “you come here RIGHT NOW!”
    Hence the need for elaborated mother-infant
    communication. According to biological anthropologist
    Dean Falk, the first sentence was probably something like

                “you come here RIGHT NOW!”
There is one other group of mammals
with this problem -- dolphin and
whales. Infants can’t hold their breath
long, so they have to stay near the
surface while mom dives for food.
And of course they have highly
elaborate vocal communication;
probably not “language” but as close as
any nonhuman gets. Coincidence?
Hence the need for elaborated mother-infant
communication. According to biological anthropologist
Dean Falk, the first sentence was probably something like

          “you come here RIGHT NOW!”

But parent-offspring security imperatives & questions
could be handled with something far simpler than language
as we know it today (dolphins demonstrate that).


Locke & Bogin (in press, Behavioral and Brain Sciences) have a
suggestion, and it ties back in with adolescence...
Theories about the origin of
language are often based on
the assumption that we need
to communicate
INFORMATION. This is
certainly part of it, whether
the information is complex or
“just” between mother and
toddler.


Locke & Bogin ask what else
language is used for...
One answer is various forms
  of social competition.


If you’re worried your
    partner might be
    interested in person X, do
    you
a) get into a fistfight, or
b) spread a rumor that s/he
   has a particularly nasty
   STD?
{c) do something more
    mature...}
But probably the main non-informational use of language is display - showing
    off - just like a bird singing. Eloquence pays off, in competition with
 members of your own sex for mates, and in ‘sweet talking’ those potential
                                    partners.
Locke & Bogin develop an argument based on those dental
growth rate data that adolescence was inserted late into human
life histories, as a time to practice competition -- which built on
earlier “motherese” to become a venue for courting and
competing. Thus language and adolescence would co-evolve,
increases in one pushing/permitting increases in the other.
Yeah, maybe...
This is a speculative hypothesis, not yet a solidly-supported
theory.
Again, my goal is to encourage looking at humans as integrated
packages that do not clearly differentiate biology, culture and
behavior.
                Shifting to more altricial infants

                                 Brain
                               continue
                      Abrupt     grow,
           Slight     height obstetric
           brain     increase dilemma
Bipedal   expand      4’ to 6’ limiting

            Simple
             stone
             tools


  SUMMARY -- a speculative scenario
      for how we became us.
                Shifting to more altricial infants

                                 Brain
                               continue
                      Abrupt     grow,
           Slight     height obstetric
           brain     increase dilemma
Bipedal   expand      4’ to 6’ limiting

            Simple             Grandparents
             stone                begin
             tools              childcare
                Shifting to more altricial infants

                                 Brain
                               continue         More
                      Abrupt     grow,         ways to
           Slight     height obstetric         invest
           brain     increase dilemma
Bipedal   expand      4’ to 6’ limiting

            Simple             Grandparents
             stone                begin
             tools              childcare
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma
Bipedal   expand      4’ to 6’ limiting

            Simple             Grandparents
             stone                begin
             tools              childcare
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood

            Simple             Grandparents
             stone                begin
             tools              childcare
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood

            Simple             Grandparents                       Time for
             stone                begin                           learning
             tools              childcare
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood

            Simple             Grandparents                           Time for
             stone                begin                               learning
             tools              childcare
                                                           Children
                                                            invest
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood

            Simple             Grandparents                           Time for
             stone                begin                               learning
             tools              childcare     Culture
                                            elaborated     Children
                                                            invest
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood

            Simple             Grandparents                           Time for
             stone                begin                               learning
             tools              childcare     Culture
                                            elaborated     Children
                                                            invest
                Shifting to more altricial infants

                                 Brain                   Menopause,
                               continue         More       longer
                      Abrupt     grow,         ways to    helping
           Slight     height obstetric         invest
           brain     increase dilemma                                  Longer
Bipedal   expand      4’ to 6’ limiting                               childhood
                                                     ?Language?
            Simple             Grandparents                           Time for
             stone                begin                               learning
             tools              childcare     Culture
                                            elaborated     Children
                                                            invest
                   Shifting to more altricial infants

                                    Brain                    Menopause,
                                  continue         More        longer
                         Abrupt     grow,         ways to     helping
             Slight      height obstetric         invest
             brain      increase dilemma                                    Longer
Bipedal     expand       4’ to 6’ limiting                                 childhood
                                                         ?Language?
               Simple           Grandparents                               Time for
                stone               begin                                  learning
                tools             childcare    Culture
                                             elaborated         Children
The scenario shown here is oversimplified speculation.           invest

BUT: it is clear that the evolution of human life history, especially
child development and menopause, has been critical to making us
who we are.
CONCLUSION:
It is very possible that our       x
super-fat brains, with resulting
intelligence, culture, language
and all that good stuff evolved
because of some quirks of
infant development, not the
other way around.
Biocultural coevolution
or email to   jjmoore@ucsd.edu
The following slides could have been
included in the lecture, but weren’t
(unless the topics came up in questions).
    Hominid brain size evolution:

                                                       Modern
                                                       range




                                                    African apes




Comparing newborn:adult brain size ratios suggests that above
about 873cc, the pattern of brain growth would have to be
“human-like”.
      Again -- only with Homo erectus do we get “human”
                         development.
Gang attack on Goliath (based on eyewitness)


How do they do this? Sometimes large
asymmetries in numbers -- a group from
one community can gang up on a single
neighbor.
Stranger killed by group of 10 males at
Kibale. Throat torn out, testes ripped
off. Note posture. Wounds all ventral.
This potential for lethal violence at relatively little risk to the
aggressor is extremely rare.
In principle, it creates conditions in which group selection
might work, favoring cooperation, communication, and of
course, larger groups.
Homo originates about 2.4 mya.
   • stone tools
   • thickening of skull esp. in parietal region
   • by 1.8 mya, dramatic increase in stature.
This scenario invokes unusual aspects of ecology to create a demographic
context in which [?group?] selection pressure favoring complex social
strategies would be present. Being really smart finally pays off. Perhaps
controlling temper (automaticity of self-regulation; spindle cells (Allman)?
With some creativity, almost any module you want can be situated in it.
Tarahumara
 (northern
  Mexico)




In fact, we are so good at running long distances that we (I use
the term loosely) can run down animals like deer and antelope,
keeping after them until they drop.
Part of our ability to run animals
down is based on our breathing
cycle; part is based on our ability
to dump heat.
By being able to run farther, right
at the edge of heat collapse, we
could hunt animals on the savanna
with just a rock for the final bash.
But heat stress is especially hard on
the brain, as illustrated by
delirium during fever.

								
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