Summary of How Humans Evolved (ch 11 and 12) and The Hunting Apes (ch 2)

 

Most sources say the human ancestor made its last split from the rest of the primates anywhere from 5 to 10 million years ago (mya), but most sources center around 6 mya.  This is around the time that the Miocene Age tuned into the Pliocene Age.  The changes in climate during those times help explain why and how humans evolved.  About 65 mya the earth had very extreme climates.  During this time Gondwanaland broke apart and caused a dramatic shift in the climate which led to more suitable living conditions.  At this time tropical rain forests spread to 60 degrees latitude north and south, close to present day London.  This created a niche for an arboreal lifestyle and the primates evolved.  Around 6mya, the climate rapidly cooled and the rain became less frequent and more seasonal.  This led to the disappearing of the rain forest and the introduction of the savannas. 

The savannas, patchworks of open grassland with occasional trees and fairly dense woodland, created a new niche in an area that was once entirely tropical forest.  In the newly created savannas animals with improved terrestrial locomotion were able to survive better than their arboreal ancestors.  Seasons in the savannas alternated wet and dry.  The wooded areas were very dense and supported browsers (leaf and stem eating animals).  The grassland areas supported fast moving grazers (grass eaters).  The terrestrial systems were better suited for both the woodland and grassland areas of the savanna.

In looking for a human ancestor, one should focus on a primate that became bipedal.  Because the human is the bipedal mammal, this is a logical place to start. According to Boyd, author of How Humans Evolved,  Australopithecus afarensis was the nearest common ancestor.  Other than the Homo, Australopithecus afarensis was the only other bipedal genus of primate.  Boyd pointed out several reasons why these primates would have become bipedal instead of quadrupedal.  Bipeds and quadrupeds had the same energy efficiency as each other, but the knuckle walking used by primates was less efficient than either one.  Walking upright had many advantages.  In the grass land walking upright was more beneficial because it lessened wind exposure and exposure to direct sunlight.  Another advantage was the ability to carry more on the body such as tools and food. 

What did the early humans eat?  By looking at the bones and teeth from a related species we can infer what humans ate.  By looking at the strontium verse calcium content in the bones we can see that Australopithecine robust (a related species) did not eat grasses.  Yet by looking at the amount of carbon 13 in the teeth evidence showed that they did eat grass.  This suggests that these animals ate some meat of grazing animals.  Many people idealize the early man as a great hunter, but the reality is that man probably hunted and scavenged for food.  The main evidence for this comes from scratch marks made on fossilized bones.  The angle and location of cut marks on some bones suggested that the animals were killed and eaten by humans.  Other fossils showed evidence of tooth marks which suggested a scavenged animal.

            Craig Stanford questioned the practice of eating meat.  He felt that because humans did not have the digestive tract of a carnovore, this meant that too much protein would be toxic to the human body.  Stanford believed that the main reason humans did eat meat was for the high fat content contained within the meat.  This fat content was found in concentrated amounts in the brain and bone marrow.  Carnivores would also leave behind the head and upper body along with the bones of the animal.  If these parts were found by early man, they could then be consumed by the humans.  Early humans did not just eat meat.  They also consumed seeds and fruit.  There is evidence to support this belief because of two things.  The human digestive track could handle no more than fifty percent of its diet from animal.  If early man was solely a grazer or a browser, the thin coat of enamel over the dentin would wear down much too quickly.  Early humans also ate large amounts of insects, including termite grubs, which were especially high in fat and protein.

            Boyd believed that we could study chimpanzees and remote human tribes to gain a better understanding as to how our ancestors would have lived and acted as we evolved closer to modern man.

            Stanford emphasized that modern humans needed to keep in mind that any idea of evolution was simply a model and that it could either be very accurate or incredibly inaccurate.  He gave an example of aging.  Stanford said that if you looked at an old house that had been restored several times, that it would be impossible to imagine what the house had originally looked like.  In looking at early man, it is hard to reconstruct 6 million years of “restoration” of evolution from apes to modern human tribes.  Stanford also pointed out that the environment had changed as well over the past several million years.  These changes need to be taken into consideration when contemplating the evolution of man.

 

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Most sources say the human ancestor made its last split from the rest of the primates anywhere from 5 to 10 million years ago (mya), but most sources center around 6 mya.  This is around the time that the Miocene era tuned into the Pliocene era.  The changes in climate during those times help explain why and how humans evolved.  About 65 mya the earth had very extreme climates.  During this time Gondwanaland broke apart and caused a dramatic shift in the climate that led to more suitable living conditions.  At this time tropical rain forests spread to 60 degrees latitude north and south, close to present day London.  This created a niche for an arboreal lifestyle and the primates evolved.  Around 6mya, the climate rapidly cooled and the rain became less frequent and more seasonal.  This led to the disappearing of the rain forest and the introduction of the savannas. 

The savannas, patchworks of open grassland with occasional trees and fairly dense woodland, created a new niche in an area that was once entirely tropical forest.  In the newly created savannas animals with improved terrestrial locomotion were able to survive better than their arboreal ancestors.  Seasons in the savannas alternated wet and dry.  The wooded areas were very dense and supported browsers (leaf and stem eating animals).  The grassland areas supported fast moving grazers (grass eaters).  The terrestrial systems were better suited for both the woodland and grassland areas of the savanna.

In looking for a human ancestor, one should focus on a primate that became bipedal. According to Robert Boyd, author of How Humans Evolved, Australopithecus afarensis was the nearest common ancestor.  Other than the Homo, Australopithecus afarensis was the only other bipedal genus of primate.  Boyd pointed out several reasons why these primates would have become bipedal instead of quadrupedal.  Bipeds and quadrupeds had the same energy efficiency as each other, but the knuckle walking used by primates was less efficient than either one.  Walking upright had many advantages.  In the grass land walking upright was more beneficial because it lessened wind exposure and exposure to direct sunlight.  Another advantage was the ability to carry more on the body such as tools and food. 

What did the early humans eat?  By looking at the bones and teeth from a related species we can infer what humans ate.  By looking at the strontium verse calcium content in the bones we can see that Australopithecine robust (a related species) did not eat grasses.  Yet by looking at the amount of carbon 13 in the teeth evidence showed that they did eat grass.  This suggests that these animals ate some meat of grazing animals.  Many people idealize the early man as a great hunter, but the reality is that man probably hunted and scavenged for food.  The main evidence for this comes from scratch marks made on fossilized bones.  “The evidence from tool marks on bones indicates that humans sometimes acquired meaty bones before, and sometimes after, other predators had gnawed on them” (415).  The angle and location of cut marks on some bones suggested that the animals were killed and eaten by humans.  Other fossils showed evidence of tooth marks, which suggested a scavenged animal.

Boyd also focused on the fact of differentiating diets among chimpanzees, which may have led to the sexual division of labor in humans.  Among chimpanzees, hunting mammalian prey was mainly a task for the males, while the females mainly hunted insects.  A list of foraging strategies was compiled to give explanations for sexual division of labor.  First, the males were larger and therefore had more physical strength to attack mammals.  Males were also able to travel longer distances than females, thereby following prey until an attack was right.  Males were also less likely to have prey stolen from them by other animals and the males were not slowed down like females because they did not have infants with them.  These patterns are evident in modern man and may have been carried through the evolutionary process.

In studying the lives of early hominids, Boyd focused on the issue of hunting and gathering.  He made the point that most large mammalian carnivores were both hunters and gatherers (412).  Boyd stated that most of the time these two activities complimented each other.  Boyd also realized that sometimes, depending on the environment in which the hominids resided, they could be either a hunter or a gatherer because of what the surroundings had to offer. 

            Boyd believed that we could study chimpanzees and remote human tribes to gain a better understanding as to how our ancestors would have lived and acted as we evolved closer to modern man.

            Craig Stanford, author of The Human Apes, emphasized that modern humans needed to keep in mind that any idea of evolution was simply a model and that it could either be very accurate or incredibly inaccurate.  He gave an example of aging.  Stanford said that if you looked at an old house that had been restored several times, it would be impossible to imagine what the house had originally looked like.  In looking at early man, it is hard to reconstruct 6 million years of “restoration” of evolution from apes to modern human tribes.  Stanford also pointed out that the environment had changed as well over the past several million years.  These changes need to be taken into consideration when contemplating the evolution of man.  Stanford summed it up perfectly in this statement:

When bipedal posture is adopted, the circulatory system, the spinal column, the diet and foraging behavior, and even the mode of social interaction also change.  This makes assembling the puzzle retrospectively an enormous challenge.  In constructing theories of our origins, we amass diverse evidence from fossils, modern human behavior, the behavior and anatomy of living primates and from genetic studies to develop conceptual models of what our earliest ancestors were like (18). 

Stanford wanted to emphasize the importance that current studies were not focused primarily on the scenarios of one closely related species, but that the studies focused on many different species in order to make more connections between modern day man and his distant relatives.

Stanford pointed out some key adaptations that occurred during the evolution process.  “When imagining the common ancestor of all hominids, the key character is bipedalism, arising at least five million years ago and exhibited by no other primate.  Our very large and complex brains, our tool-using capabilities, the increased amounts of meat in our diet, and our unusual social system all evolved at much later dates” (43).  The adaptation to bipedalism had many advantages to earlier forms of locomotion. 

Being upright gives a height advantage to intimidate predators and other hominids.  Being upright allows an early grassland hominid to see over tall grass.  Being upright reduces one’s exposure to intense tropical sun and heat, thereby reducing heat stress on the savannah.  Being upright is not about walking, but rather about posture when foraging.  The bipedal posture may have evolved to allow apes to pull down low-hanging, fruit-laden branches or to allow for better tree-climbing ability on vertical trunks.  An upright walker has its hands freed for carrying food, offspring or tools (45). 

This led Stanford to study issues of a carnivore lifestyle.

Stanford questioned the practice of eating meat.  He felt that because humans did not have the digestive tract of a carnivore, this meant that too much protein would be toxic to the human body.  Stanford believed that the main reason humans did eat meat was for the high fat content contained within the meat.  This fat content was found in concentrated amounts in the brain and bone marrow.  Carnivores would also leave behind the head and upper body along with the bones of the animal.  If early man found these parts, the humans could then consume them.  Early humans did not just eat meat.  They also consumed seeds and fruit.  There is evidence to support this belief because of two things.  The human digestive track could handle no more than fifty percent of its diet from animal.  If early man were solely a grazer or a browser, the thin coat of enamel over the dentin would wear down much too quickly.  Early humans also ate large amounts of insects, including termite grubs, which were especially high in fat and protein.

Meat eating and hunting and gathering were big areas of concern.  He supported the fact that there were sex-linked roles among the ancestors.  Men did the hunting and women did the gathering.  The importance of meat was undermined during a conference in Chicago in 1966.  “Perhaps the foremost scientific conclusion that came out of the meeting was that the importance of meat in the diets of foraging people had been exaggerated.  This was deeply ironic, since the most influential and ultimately notorious perspective to emerge from the meeting came to be known as ‘Man the Hunter’” (37).  This showed that people still had the misconception of early man being a hunter when in reality he was more of a gatherer and scavenger. 

            Stanford also discussed the idea of a “missing link”.  The idea of a missing link was ever present in the minds of modern man.  “By definition, the missing link is the most recent common ancestor of both humans and great apes, which must have lived immediately before the split of these two lineages in the late Miocene or earliest Pliocene era” (33).  In reality, Stanford stated that there was no such thing as a missing link or a “most recent common ancestor” (33).  Giving an explanation for the idea of a missing link, Stanford explains that it is simply a metaphor for the process of speciation that preceded the emergence of hominids.

            Both Boyd and Stanford have made arguments that are related to each other.  The conclusion is that early man was both a hunter and a gatherer that was carried over through the evolutionary process from primates.  Bipedalism evolved from quadrupedalism to become the dominant way of locomotion.  A sexual division of labor was evident among both chimpanzees and early man.  The importance of fat in the daily diet in early life has carried over through the years and is evident among current man.  Evolution did not occur quickly, but rather throughout millions of years and is still occurring.  Change is not evident over night but over time. 

 

 

Outline

 

A.      Robert Boyd, author of How Humans Evolved and his opinions on primate evolution

 

  1. Primates evolved from quadrupeds to bipeds for efficiency and convenience

a.        Although bipeds and quadrupeds used the same energy as each other, the knuckle walking was less efficient

b.       In grassland walking upright lessened wind exposure and exposure to direct sunlight

c.        Upright motion allowed more freedom to carry more on the body such as tools, food, and infants

2.     Early humans ate both meat and vegetation

a.        Evidence shows that the Australopithecus ate animals that were herbivores

b.       Early man was probably a scavenger and did not hunt as much as was initially thought

c.        Scratch marks on bones show evidence of both tools used to cut meat and tooth marks used from animals to scavenge the dead animal

d.       In general, most large mammalian carnivores were both hunters and gatherers, meaning that the two activities complimented each other

e.        The conditions of the environment often determined whether the hominid was a hunter or a gatherer

3.     Differentiating diets among chimpanzees may have led to the sexual division of labor in humans

a.        Among chimpanzees, hunting for mammalian prey was generally done by the males while females hunted for insects

(1)     Several reasons for the division of labor were that the males were larger and therefore had more physical strength to attach mammals

(2)     Males were able to travel longer distances than females, thereby following prey until attacking

(3)     Males were less likely to have prey stolen from them by other animals

(4)     Males were not slowed down like females due to the carrying of infants

 

B.       Craig Stanford, author of The Human Apes, and his ideas of restoration and evolution, pertaining to adaptations of hominids and the “missing link”

 

1.  Evolution could be either very accurate or very inaccurate

2.     The ideas of restoration and evolution could go hand in hand

Imagine a house being restored over time until it looks nothing like it used to.  The restoration and evolution of the house have changed it over time so that the house no longer is the original.  The same can be applied when thinking of the evolution of hominids.  The environmental and hominidal changes that have occurred need to be taken into consideration when looking at evolution.

3.     The main adaptation that occurred during evolution was the switch from quadrupeds to bipeds which was advantageous for several reasons

a.     A height advantage could be used to intimidate predators

b.    The height could be used to see over tall grasses

c.     It reduced exposure to intense tropical sun and heat, which reduced heat stress

d.    The newly acquired posture allowed hominids to pull down low hanging branches filled with fruit and allowed for better tree-climbing abilities on vertical trunks

e.     Hands were free to carry food, offspring or tools

4.     Meat eating was not practical for early man, but was practiced for the high fat content

a.        Too much protein was toxic for the body, so early hominids ate meat primarily for the high fat content

b.       Early hominids also ate seeds, fruit, and insects, which were high in protein

5.     Sex-linked roles were found among ancestors

a.        Men did most of the hunting while women primarily did the gathering of seeds and fruit

6.     Early man was not necessarily a hunter, as was originally thought

a.        Although early man was though of as a hunter, he was primarily a gatherer and scavenger

7.     The “missing link” theory was not a valid theory

a.  Although the “missing link” was a thought always present in the minds of modern man, it was simply a metaphor to explain the process of speciation that preceded the emergence of hominids