Primate life Shares a general developmental pattern with other mammals

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

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

3. Primate life Shares a general developmental pattern with other mammals Adulthood

4. Primate life Shares a general developmental pattern with other mammals Then something happens...

5. And we are primates too...

6. very rapid growth, but rate falling fast sudden rapid growth again, then rapid fall in rate slower, even growth growth rate drops growth stops But development is not just marking time -- there are PATTERNS to growth. What’s up with that?

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

8. Bogin says that nonhuman primates don’t have growth spurts; theyDO (in weight, if not height). 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. Adolescent growth spurt

9. Duration of adolescent growth spurt in primates 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. male men women female From Leigh 1996: Fig. 12

10. What is odd about humans is NOT the length of our growth spurts, but how late they start. From Leigh 1996: Fig 13

11. The way to get a late start to the adolescent growth spurt HERE ...

12. 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????

13. 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 compared across Orders. For example, on average Primates mature later and live longer than other mammals. a = maturity

14. 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, ahigh value of calf:mother is a sign of greater investment by mother. Why should older mothers invest more?

15. 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?

16. 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?

17. Why do primates in general extend the immature period? M = lifespan a = sexual maturity Age at sexualmaturity and total lifespan are both greater (for a given body weight) in primates. Long life seems nice, BUT...

18. Being immature longer has a reproductive COST !! Evolutionary theory predicts there must be a benefit that is greater than that cost.

19. 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...

20. 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.

21. 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.

22. 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

23. 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.

24. 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.

25. 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.

26. 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...

27. 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).

28. 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.

29. 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.

30. 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.

31. Bipedalism represents a major change in posture, which creates a problem not usually faced by quadrupeds: Tipping over.

32. 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)

33. 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.

34. 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, ...

35. ... 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.

36. The “obstetric dilemma” (chimpanzee) (modern human) (Australopithecus) Blue arrows indicate direction baby facing; mother’s stomach is facing upwards. 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. Note that human infant has to twist, and then face toward mother’s back. What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

37. The “obstetric dilemma” (chimpanzee) (modern human) (Australopithecus) Blue arrows indicate 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.

38. The “obstetric dilemma” (chimpanzee) (modern human) (Australopithecus) Blue arrows indicate direction baby facing; mother’s stomach is facing upwards. Note that human infant has to twist, and then face toward mother’s back. What does that pelvic narrowing & brain expanding do for giving birth? Ouch.

39. 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???

40. Give birth “earlier” in development, and let the brain do some of its growing outside. Nonhuman primate brain growth pattern is fairly consistent: fast growth in utero, then slowing after birth. Birth Rhesus monkey Human pattern looks the same, but fast growth doesn’t start to taper off until > 3 months old. We are born premature. 1 year old Birth Human

41. 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.

42. 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?

43. 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.

44. 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?

45. Juveniles & children can help produce more children, by helping with those ‘premature’ babies.

46. Why menopause? Grandparents (grandmothers especially) can also help directly, as well as indirectly through their knowledge and wisdom.

47. Though both human and chimpanzee females stop reproducing by age 50, we just keep on going... Chimpanzee

48. 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.

49. 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.

50. 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.