Life in the Trees video notes (rev 1/23/12)



1. basic features of primates

(Notes for "Life in the Trees" video, revised,)

This video was made about 1977-8. Despite a few inaccuracies from a current perspective, it remains an excellent production. It demonstrates the basic features of primates, has a number of insights into evolution of humans, and is without the drama, cheesy soundtrack and romantic -- often exaggerated anthropomorphic -- commentary in more recent videos.


The video reveals the basic primate patterns of morphology and behavior. The trend over 60 million years is to increasingly better color vision with lesser reliance on olfaction, more skilled grasping forelimbs, and cogntion based on brain size. Primates also have increased in overall size, evolved greater social skills and continued a long period of maternal care of offspring.

The discussion --in connection with howler monkeys --of why size tends to increase and the limits on this is important. This shows us why a simplistic "survival of the fittest" does NOT entail that size and strength determine fitness. While this may be true in some species at some points in evolution, what determines fitness (the extent to which your genes are represented in subsequent generations) varies from situation to situation.,

1. binocular vision

Observe forward facing eyes with overlapping visual fields. Most monkeys and apes are day-living and have good color vision as well.  This may have been triggered by the enhanced foraging skills for ripe fruits – red ones.  Good color vision is also necessary for the use of color in mating activities – -- primates are the most colorful mammals.

These visual features illustrate a basic point of evolution -- the form or structure of primates can be used to predict their behavior. Forward facing eyes susggest better binocular vision, with correspondingly less peripheral vision. The depth perception enabled by binocular vison may be more useful to predators (e.g. cats) and/or tree-dwellers (e.g. monkeys) than prey species like deer or horses.


Similarly, the presence of cones required for color vision, suggest diurnal or dayliving species rather than nocturnal ones. Only a few primate species lack a rich supply of cones in the fovea of their eyes. Recently it has been found that even the nocturnal aye-aye has a complete set of color genes

2. grasping paws and flexible forelimbs

Useful in feeding, climbing, clinging, grooming. And adaptable to many other uses when attached to a larger brain

It is possible that these flexible forelimbs also enhanced brain size in order make the fingers work more effectively together. The flexibility of these five digits contrasts with the modifications of these same five digits in other species like elephants and dolphins.

3. care of young

Take them along! High "parental investment" -- primate females necessarily invest much time and energy in their single offspring and for some species, the males do too. Relative to other mammals, primates have fewer nipples, tend to be slow maturing and highly dependent on maternal care for that period.  Why are primate twins so rare? What other advantages might this close mother-young relationship offer? Recall the discussion of Imo, the Japanese monkey.

4. relatively large brain, especially neocortex

Consider costs and benefits of this brain!  Auto engines make a good analogy – big engines can do more,  go faster, but require lots of fuel and a good exhaust system. And require better cooling and stronger shocks etc.  (They also may disrupt the environment more!!)

5. most primates are highly social

this brings social complexity of dominance, mating, and other relationships.  For example predicting and controlling fellow hominids requires a different set of skills than manipulating inanimate objects.It has been demonstrated that more social primates tend to have relatively lalarger neocortical areas. (See Dunbar readings.)

6. all of the above predict highly intelligent creatures

Why?   Any answer to this would invoke brain size and complexity and the adaptation of brain structures evolved for one function to be extended to other novel functions.

2. adaptation , radiation, differentiation

variation and natural selection, "fitness" & niches

While all primates are based on the same genetic "plan," millions of years of variation and selection have differentiated primates into about 222 species. You should be able to outline this plan and the variations of the plan.

the close relation between form and function

Behavioral capabilities often can be predicted from physical features.  Examples seen in the video include shift to binocular vision, shift from olfaction to vision as the dominant sense, sexual dimorphism,  shift to homind bipedalism, and even comparisions of tooth size and shape reflecting changes in diet.. See "primates in the news" for recent research on the sisignificance of diet. (Those gorillas shown laying around after eating are also digesting a large amount of low calorie leaves and bark in a specially evolved digestive tract.)

regulatory genes and neoteny (Gould, 1977 -"Ontogeny and Phylogeny" ch.10 for a historical discussion)

Primates can all be seen as variations on the same mammalian "plan", often with identical structures "built" by nearly identical DNA codes. Neoteny is an old concept referring to retention of juvenile features into adulthood. The more general process is "heterochrony" or differences in timing that can "build" different variations on the same plan.

Some genes regulate growth rates, e.g. by timing and varying growth hormone levels, etc.
This is an important means of developing the unique features of each species -- for example, grow forelimbs a little more or less, reduce the olfactory brain a bit, etc. This is an old idea probably going back to the early 1900s but only recently has any specific evidence been reported.

3. varieties of primates

1. lemurs, loris, tarsiers

Living descendants (prosimians) of early primates some 50 mya. Fossil evidence is uncertain on details.   See "Overview" notes. Hiw did lemurs get on Madadascar?

1. modes of communication and environment

1. Contrasting scent vs call-using species

2. diurnal and nocturnal

vision and audition differences

2. monkeys -

Monkeys replaced prosimians in many niches; with one exception (owl monkey), monkeys are day time creatures with excellent color vision. Some new world monkeys have developed prehensile (grasping) tails. Monkey species vary considerably in appearance and abilities but are generally thought to be more intelligent than prosimians and transitory species to apes and humans.

1. new world (50 varieties in SA)

1. marmosets

most primitive, South American, squirrel-like

2. squirrel monkey

3. howler monkey

loudest mammalian noise, grasping tail, vegetarians, relatively weak sense of smell (note shape of skull and brain associated with these senses), role of color (eyes, social/sexual displays, fruit)

2. other monkeys (Africa & Asia) "old world monkeys"

no prehensile tail, not as exclusively adapted to trees

1. vervets

African ground dwelling, elaborate calls denoting specific threats

2. baboons

ground dwellers, large males, omnivores, visual signals (eyebrow flash).  Baboons have often served as "models" of human evolution despite being monkeys. They have strick dominance hieratchies and complex "politics." We may see more of them.

3. macaque monkeys

all over Asia, Gibraltar, to snow in Japan, all very adaptive to wide variety of environments. The narrator suggests the habit of washing sweet potatoes in a group of Japanese macaques demonstrates the possibility of culture. This is a controversial interpretation -- maybe each one learned on their own, facilitated by being near others, especially their mothers.  In any case, it is interesting and macaques are well equipped to survive in competition with humans .

4. Asian tree monkeys

large tree dweller

3. apes

These are humans closest relatives and all have differentiated over the past 15-20 million years. All are intelligent and have varied social structures and diets. See "Children of eve" and readings for info on how relationships and timing are determined.

1. Asian apes -

1. orangutans

walking in the trees (see Orang video) Many have fractures.

2. gibbons (and close cousins simiangs )

smaller, more agile tree-dwelling apes, jumping and swinging through trees, many fractures (1/3 of all have broken bones).  While all apes including humans use vocalization for communication,  gibbons and humans seem to be unique in melodic control of voice. Gibbons are the most distantly related ape to humans.

2. African apes

1. gorilla

increased dexterity and sensitivity of hand, less equipotential feet, largely ground dwelling--eating, grooming, resting. Gorilla behavior is to a large extent governed by their diet -- widely available low calorie leaves, bark, even wood. They need to eat a lot of this and have specially adapted digestion to extract nutrients from these foods.

2. chimps

omnivores (largely vegetarian though they would eat whatever meat – termites, monkeys – they can get), still an agile tree dweller (size, foot remains dextrous, spends evening in tree nest), highly individualized faces, large, highly structured social groups (20-50), social function of grooming, simple "tool" use. Our closest primate "cousin."

This older video does not show us the bonobo chimps, close cousins but differing in behavior to the more common chimps.

3. hominid ancestors (many today include African apes as well as homo X)

Chimps, including bonobos, and humans separated by 5-7, not 15 million years!
"Lucy" first walking hominid (4 mya)
"homo habilis" tool-making ancestor (2.5 mya) with small but increasing brain size. Of course we have not yet uncovered all the fossil remains that might show up at any time.

Recent comparisons of Lucy's species with humans suggests they were much less sexually dimorphic than orangutans and gorillas.  They also had teeth suggesting a diet including lots of meat.