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...

Primates are characterized by slower rates of development, carried to an extreme in the

great apes and humans.

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

Monkey in the Mirror

Rates of development can be dramatically different

These blesbok (a South African antelope) are mobile almost immediately - you’re seeing birth to running almost in real time.

Wild Things: Nature’s Babies

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

very rapid growth, but rate falling

fast

slower, even

growth

sudden rapid growth

again, then rapid fall in

rate

growth stops

growth rate drops

After Bogin 2006, Fig. 7.3

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

INFANT

CHILD

JUVENILE

ADOLESCENT

ADULT

After Bogin 2006, Fig. 7.3

Bogin says that nonhuman primates don’t have growth spurts in height; they DO, in weight. But what does height mean to a quadruped, anyhow?Many primates share

this pattern of

growing FAST in

utero [not shown],

then slowing down

for a while, and

finally showing a

growth spurt just

before adulthood.

Many primates share

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 spurtAdolescent

growth spurt

From Leigh 1996: Fig. 12

Each point represents male (o) or female (∆) of a different primate

species.

Our growth spurts last about as long

as expected for our body size.

female

male

Duration of adolescent growth spurt in primatesDuration of adolescent growth spurt in primates

men

women

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 ...

Why do humans turn growth off? Is there a reason????

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

... is to turn growth off

HERE

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

Basic life histories can be compared across Orders. For example, on average Primates mature later and live longer than other mammals.

M = lifespan

α = maturity

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

“Nature has ensured”- shorthand for natural selection acting on pattern of behavioral development.

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

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?(Mother and calf shot when calf ≈ 6 months old.)

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?

Does the life-history perspective MATTER?

Some school grades start class at ≈ 9am; some start before 8am. Which should start before 8am?

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?

Age at sexual maturity and total lifespan are both greater (for a

given body weight) in primates. Long life seems nice, BUT...

M = lifespan

α = sexual maturity

Being immature longer has a reproductive COST !!

Evolutionary theory predicts there must be a benefit that is greater than that cost.

Evolutionary theory predicts there must be a benefit that is greater than that cost.

Primates are unusual in that wetend to live in stable groups. This has a lot of advantages…but means young sometimes are competing with adults for food.

NOT a good idea...

Primates are unusual in that wetend to live in stable 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.

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.

And this helps to explain two puzzles introduced earlier.

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

Adolescent growth spurtAdolescent

growth spurt

Note that in all the

great apes, the

spurt is more

dramatic for males --

why?

Good reason to think

these are connected.

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

When quadrupeds

fight, they typically

use their teeth --

after all, hands have

to be adapted for

walking.

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

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.

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

And they can do it

pretty effectively.

Notice the use of

height to both look

more intimidating

and provide more

force for a blow.

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

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...

What does height mean to a quadruped, anyhow?

Back to an earlier question:Back to an earlier question:

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?

II. Why do humans take this to such an

extreme?

Key points:

1) the line leading to us shared an ancestor with the line leading to chimpanzees about 5-7 million years ago.

Key points:

1) the line leading to us shared an ancestor with the line leading to chimpanzees about 5-7 million years ago.

More than you wanted to know about human evolution.

II. Why do humans take this to such an

extreme?

II. Why do humans take this to such an

extreme?

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.

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.

More than you wanted to know about human evolution.

II. Why do humans take this to such an

extreme?

II. Why do humans take this to such an

extreme?

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.

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.

More than you wanted to know about human evolution.

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)

We did all three.

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.

Chimpanzee Human

Australopithecus

(pelves not to scale)

African apes

Modern range

Hominid brain size evolution:Hominid brain size evolution:

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.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

The “obstetric dilemma”(chimpanzee)

(Australopithecus)(modern human)

Blue arrowsindicate direction baby facing; mother’s stomach is facing upwards.

Note that human infant has to twist, and then face toward mother’s back.

As the fetus begins to descend, there

is plenty of room for the chimpanzee

(facing forward); hominids have to

face sideways but there is room.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

The “obstetric dilemma”(chimpanzee)

(Australopithecus)(modern human)

Blue arrowsindicate direction baby facing; mother’s stomach is facing upwards.

Note that human infant has to twist, and then face toward mother’s back.

At the halfway point, chimp is still OK. Australopithecus manages shoulders with small bend of neck, but human has to rotate to facing backwards.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

The “obstetric dilemma”(chimpanzee)

(Australopithecus)(modern human)

Blue arrowsindicate direction baby facing; mother’s stomach is facing upwards.

Note that human infant has to twist, and then face toward mother’s back.

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???

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???

Nonhuman primate brain growth pattern is fairly consistent: fast growth in utero,then slowing after birth.

Human pattern looks the same, but fast growth doesn’t start to taper off until > 3 months old.

We are born premature.

Give birth “earlier” in development, and let the brain do some of its growing outside.

Give birth “earlier” in development, and let the brain do some of its growing outside.

Rhesus monkey

Birth

Birth

1 year old

Humancf. Bogin 2004 Fig. 7.5

Modern human infants are born with relativelyless-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 relativelyless-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 relativelyless-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?

Modern human infants are born with relativelyless-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:

Chimpanzee Human1st molar 3.3 6

1st incisor 6 6.5

Permanent teeth erupt at different ages in apes & humans:

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.

Grandparents (grandmothers especially) can also help directly,

as well as indirectly through their knowledge and wisdom.

Why menopause?

Though both human and chimpanzee females stop reproducing by age 50, wejust keep on living...

Chimpanzee

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 (they’d all fit in 2 football stadiums).

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.

III. How does this extreme extension of immaturity relate to understanding what modern humans are all about?

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...

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 (like the blesbok).

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?

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 (2006*) have a suggestion, and it ties back in with adolescence...

* Language and life history: a new perspective on the development andevolution of human language. Behavioral and Brain Sciences 29: 259-280

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 elselanguage 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.

Bipedal

Simple stone tools

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

SUMMARY -- a speculative scenario for how we became us.

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcare

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

More ways to invest

Simple stone tools

Grandparents begin

childcare

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcare

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcare

Longer childhood

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcare

Longer childhood

Time for learning

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcareChildren

invest

Longer childhood

Time for learning

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcareChildren

invest

Longer childhood

Time for learning

Culture elaborated

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcareChildren

invest

Longer childhood

Time for learning

Culture elaborated

More ways to invest

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcareChildren

invest

Longer childhood

Time for learning

Culture elaborated

More ways to invest

?Language?

Menopause, longer helping

Simple stone tools

Bipedal

Slight brain

expand

Abrupt height

increase 4’ to 6’

Shifting to more altricial infants

Brain continue

grow, obstetric dilemma limiting

Grandparents begin

childcareChildren

invest

Longer childhood

Time for learning

Culture elaborated

More ways to invest

?Language?

Menopause, longer helping

The scenario shown here is oversimplified speculation.

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.

Simple stone tools

x

CONCLUSION:

It is very possible that our 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. I.E., the human extension of immaturity did not originate “to give us time to learn”.

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).

African apes

Modern range

Hominid brain size evolution:

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)Gang attack on Goliath (based on eyewitness)

How do they kill? 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 - he was held down.

Stranger killed by group of 10 males at Kibale. Throat torn out, testes ripped off. Note posture. Wounds all ventral - he was held down.

Male lethal aggression in chimpanzees

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.