Prologue
Humans are unlike all other species of animals in that we are most evolved but yet don’t quite understand how and why it came to be so. We are so much better that we developed a separate category for all other species, “animals”. These “animals” share characteristics that with each other but not with “us”. Instead, we are able to write, build, utilize machinery, and “talk”. Other less favorable humanistic qualities are the acts of committing genocide, using addicting drugs, and destruction of other animal species.
In 1859 most people viewed Darwin’s theory as absurd. Today, twenty-five percent of all college graduates believe God created humans.
We are very similar to other animals with respect to body parts, molecules, and genes. Strip away our clothes and throw us into a cage and we are just a chimpanzee. “Molecular genetic studies of the last half-dozen years have shown that we continue to share over 98 percent of our genetic program with the other two chimps. The overall genetic distance between us and chimps is even smaller than the distance between such closely related bird species as red-eyed and white-eyed vireos.” (Diamond, 2) These other two chimps are the pygmy chimp of Zaire and the common chimp of the rest of tropical Africa. Since Darwin there have been numerous intermediary fossils between that of apes and humans found.
The findings that lead us to conclude that we are so very similar to chimps only lead us to more curious questions. The few bits of new baggage we acquired---the two percent difference between our genes and those of chimps—must have been responsible for all of our seemingly unique properties.” (Diamond 2) Within a period of a few tens of thousands of years we began to display qualities that make us unique to all other species. If it has only been a few tens of thousands of years then there must have been pre-cursors to art, language, and genocide found in other “animals”.
We are unlike any other animal in that we populate all areas of the world, there is no other large animal that can compete with us in terms of numbers, and there is no other animal that has the ability to destroy their environment as we do. The prophecy that the world is likely to come to an end soon is very real to us now for two reasons. (1) The development of nuclear weapons gives us the means of wiping out whole countries and civilizations. (2) Already we consume forty percent of the world’s net productivity. Future considerations that we must consider are the population boom and our tendency to kill off, not only our species, but all other animal species too.
We as a species can change the path we are set on. Even if the tendency to murder strangers or competitors is innate to us… we have shown that we can suppress those feelings. “Even taking two world wars into account, proportionately far fewer people have died violent deaths in twentieth-century industrialized states than in Stone Age tribal societies.” (Diamond, 4) The purpose of this book is to help us to not repeat our past mistakes. “What is lacking is the necessary political will. Through this book I seek to foster that will, by tracing our history as a species. Our problems have deep roots tracing back to our animal ancestry. What we do now will effect our world well into the next century.
Our human existence is divided into five parts. “In the first part I’ll follow us from several million years ago until just before agriculture’s appearance ten thousand years ago. These two chapters deal with the evidence of bones, tools, and genes---the evidence that is preserved in the archaeological and biochemical record, and that gives us our most direct information about how we have changed… we’ll try to figure out what differences of two percent was responsible for our great leap forward.” (Diamond 7)
The second part delves into some of our social practices. These social practices include “feeding our children after the age of weaning, instead off leaving them to find food on their own; that most adult men and women associate in couples; that most fathers as well as mothers care for their children; that many people live long enough to experience grandchildren; and that women undergo menopause.” (Diamond 7)
Part three sets to examine some of the traits that set us apart from other animals. “Those that come first to mind are the ones of which we are proudest: language, art, technology, and agriculture, the hallmarks of our rise.” (Diamond 8) Part three also discusses some of the animal precursors leading into the human species.
Part four examines the “black traits” which we exhibit; “our propensity for xenophobic killing of other human groups. This trait has direct animal pre-cursors—namely, the contests between competing individuals and groups that, in many species besides our own, may be resolved by murder. We’ll see how technology, culture, and geography affected the outcome of two of the most familiar historical sets of contests between human groups. We’ll then survey the worldwide-recorded history of xenophobic mass murder. The other black trait is our harming of the environment. “This behavior too has its direct animal precursors. Animal populations that for some reason or another escaped control of predators and parasites have in some cases also escaped their own internal controls on their numbers, multiplied until they damaged their resource base, and occasionally eaten their way into extinction.” (Diamond 8)
Part five seeks to debunk the fantasy that this sort of destructive behavior did not appear in us until the Industrial Revolution. It does so by “facing up to our long history of environmental mismanagement.” (Diamond 9)
The book then concludes with an epilogue that traces us back to our ancestral origins. “It also traces the acceleration in our means to bring about our fall. (Diamond 9)
In determining whether or not our genes differ from the genes of chimpanzees it is crucial that we look further than physical appearance. Physical appearance can be deceiving because it would appear that a Great Dane and a Pekinese would not be able to mate, but this is not the case. Even though they look so very different, they are still considered to be of the same species and can therefore breed. A new method developed within the last half dozen years allows us to measure genetic differences between animal species. By the study of molecular genetics, we are now able to measure the genetic differences between humans and chimps and the approximate elapsed time since our divergence (seven million years). The findings of molecular genetics also raise the ethical question of, "How we should go about treating chimps?"
Even though our molecular genetics results give us information on genetic distance and elapsed time, they cannot tell us how specifically we differ and when those specific differences appeared. This is when the study of anthropology (study of bones and tools) can benefit us greatly. “The changes in bones constitute the traditional subject matter of physical anthropology. Especially important were our increase in brain size, skeletal changes associated with walking upright, and decreases in skull thickness, tooth size, and jaw muscles.” (Diamond 12)
A common myth was that the evolution of a large brain was the key to the development of language and innovativeness. However, this was not the case. “Neanderthals had brains even larger than those of modern humans, yet their tools show no signs of inovativeness and art.” (Diamond 12) This myth helps support the molecular genetics theory. “Within that models percentage of difference between our genes and chimpanzee genes, there must have been an even smaller percentage not involved in the shapes of our bones but responsible for the distinctively human attributes of innovation, art, and complex tools.” (Diamond 13)
Consider grouping a bunch of chimps together, shaving them, and then locking them up in a cage. Next, take the same number of human beings and strip them of their clothing. Lock them up in a cage next to the chimps. Would it be that easy to differentiate the two groups? Why is it if chimps and humans are so genetically similar that we are able to display chimps in a zoo and also experiment with them in a laboratory? How ethical would it be to experiment on chimpanzees if we discovered that they were 99.9% similar to us? If we are allowed to experiment on similar but genetically “lesser” animals, then who is to say we cannot conduct laboratory experiments on the mentally ill? Obviously, many ethical questions have been raised as a result of molecular genetics.
Humans are classified as mammals by having hair, nursing their young, and other features. We are further classified as Primates because we have flat fingernails, an opposable thumb, toenails as opposed to claws, and a free hanging penis. Animals that are classified as primates include the apes (gibbons, orangutans, gorillas, chimpanzees), monkeys, and humans. We are most similar to apes. “It’s also clear that gibbons, with their small size and very long arms, are the most distinctive apes, and that orangutans, chimpanzees, gorillas, and humans are all more closely related to each other than any is to gibbons.” (Diamond 16) To dig deeper has caused much scientific debate.
The scientific majority believes that we are most closely related to the chimps and the gorillas and that gorillas and chimps are more closely related to each other than we are to either of them. This would imply that we branched off at an earlier point than did chimps and gorillas from one another. Anatomical studies are useful, but they cannot tell us our approximate time of divergence and our genetic distance from apes. Anatomical evidence has also been scarce because no ape fossils have been found from about five to fourteen million years ago.
The field of molecular genetics originated about thirty years ago as scientists were examining bird taxonomy. Scientists hypothesized that certain chemicals inside organisms might provide a “clock” by which to measure genetic differences. A simple explanation goes as follows. DNA, a universal molecule that is inside organisms mutates at a constant rate. Mixing two different samples of DNA from two different organisms and measuring the change in boiling point allows for one to approximate the percent genetic difference.
The first monumental use of this new method was done by Charles Sibley, and ornithologist, and Jon Ahlquist. Deciphering different species of birds and their histories proved to be extremely difficult using just anatomical characteristics. Turning to molecular genetics, Sibley and Ahlquist were able to publish the results of seventeen hundred bird species.
Most scientists at the time dismissed this method as ludicrous. One anatomist said, “I’m sick of hearing about that stuff. I no longer pay attention to anything those guys write.” (Diamond 20) Another said, “Interesting, but their conclusions need a lot of testing by other methods before we can believe them.” (Diamond 20)
Not until 1984 did Sibley and Ahlquist speculate on the origins of humans. “The biggest genetic difference, expressed in a big DNA melting-point lowering, is between monkey DNA and the DNA of humans or of any ape. “Monkeys share 93 percent of their DNA structure with humans and apes, and differ in 7 percent.” (Diamond 22) The next biggest difference is that of gibbon DNA and human and ape DNA. “One of 5 percent between gibbon DNA and DNA of other apes or humans. This too confirms the accepted view that gibbons are the most distinct apes, and that our affinities are instead with gorillas, chimpanzees, and orangutans.” (Diamond 22) “The most similar DNAs are those of common chimpanzees and pygmy chimpanzees, which are 99.3 percent identical and differ by only 0.7 percent.” (Diamond 22) Pygmy chimpanzees are remarkably similar to us in behavior. “Unlike common chimps but like us, pygmy chimps assume a wide variety of positions for copulation, including face to face; copulation can be initiated by either sex, not just by the male; females are sexually receptive for much of the month, not just for a briefer period in midmonth; and there are strong bonds among females or between males and females, not just among males.” (Diamond 22) A common theme that should be recognized is that small differences in genetic makeup can lead to large differences in behavior.
These new results effect our traditional views of taxonomy. Traditional taxonomists have grouped species into higher or lower categories based primarily on subjective judgements of how important differences between species are. This type of classification puts humans in a separate family from that of apes primarily because of our large brain and bipedal posture. However, this subjective method of classification would remain largely unaffected by recent genetic findings. The other school of taxonomy, known as cladistics, “argues that classification should be objective and uniform, based on genetic distance or times of divergence.” (Diamond 25) Even those taxonomists who utilize cladistics have a hard time lumping humans and chimps into the same genus.
Before we can consider the question of which genes between humans and chimps differ, we must come to an understanding of what DNA is and what it does. DNA is the template to which transcription occurs. This is where some of the DNA is read and “carried” to the ribosomes via mRNA. Translation occurs at the ribosomes and results in protein synthesis. Certain proteins make up much of our body structure while other proteins serve as enzymes. Enzymes help in lowering the activation energy for biological reactions to occur thus increasing the rate of reactions. Hemoglobin is one very important protein in the body. It is responsible for carrying oxygen to the cells of the body and travels through the blood.
Tay-Sachs is a disease involving “many behavioral as well as anatomical anomalies: excessive drooling, rigid posture, yellowish skin, abnormal head growth, and other changes.” (Diamond 26) The Tay-Sachs gene affects a single enzyme in the body and this causes deleterious effects. This enzyme is responsible for breaking down a widespread cellular constituent and is ineffective in those who have Tay-Sachs.
There are some traits that are governed by a single gene or by a few genes. More complex traits such as behavior have numerous genes associated with their expression. What makes it even more difficult is much of our behavior is governed by environmental as well as genetic influences. “Behavioral differences among individual humans are obviously subject to enormous environmental influences, and it’s very controversial what role genes play in such individual differences.” (Diamond 27)
We do not know the particular genes that are crucial in our differences from chimps. Replacing an amino acid with one that is dissimilar is likely to produce a change. For instance, “the disease sickle-cell anemia is an often-fatal condition, resulting from a change in our hemoglobin’s solubility, resulting in turn from a change in just one of hemoglobin’s 287 amino acids, resulting in turn from a change in just one of the three nucleotides specifying that amino acid.” (Diamond 28) An example of the differences among individuals of related species is the cichlid fishes of Africa’s Lake Victoria. These fishes differ on what they eat just as a tiger and cow differ on what they eat. But all these Lake Victoria cichlids “differ from each other on the average by only about 0.4 percent of their DNA studied. Thus, it took even fewer genetic mutations to change a snail crusher into a specialized baby killer than it took to produce us from an ape.” (Diamond 28)
The broader questions that our findings raise is how should we think about the place of humans and apes in the universe. These new findings might change how we use apes. Today we can subject apes to lethal experiments that we cannot do to humans, should we now continue to do so? This question is more difficult to answer than the question of whether we should house apes in cages. There are humans that are caged, and this is called being thrown into jail. “Somewhere along the scale from bacteria to humans, we have to decide where killing becomes murder, and where eating becomes cannibalism.” (Diamond 30) More and more animal-rights activists object to medical experiments performed on animals. “If our ethical code makes a purely arbitrary distinction between humans and all other species, then we have a code based on naked selfishness devoid of any higher principle. If our code instead makes distinctions based on our superior intelligence, social relationships, and capacity for feeling pain, then it becomes difficult to defend an all-or-nothing code that draws a line between all humans and all animals.” (Diamond 30)
Outline
I. Society says “We are not animals”
(1) Humans are most evolved
(2) Humans write, build, and utilize machinery
(3) Humans “talk”
II. Diamond says, “We are like other animals”
A. Biologically
(1) DNA, molecules, genes
(2) Humans share 98% of genes with chimpanzees
(3) Humans vs. chimps is closer than red-eyed vs. white-eyed vireos
(4) Fossil record & the intermediares
B. Sociologically
(1) Strip us of our clothes, throw us in a cage and we are nothing more than a
third chimp
III. Crucial points that arise as a result of this similarity
(1) The two percent difference between humans and chimps must have led
to our unique difference.
(2) Within a few tens of thousands of years we became “unique” as
compared to all other species
(3) There must have been pre-cursors to language, art, and tool use.
IV Our black traits
(1) genocide
(2) use of addictive drugs
(3) destruction of other animals
(4) consumption of 40% of the world’s net productivity
(5) population growth
(6) destruction of environment
(7) nuclear weapons
V There is hope
(1) We are able to suppress our innate aggression
(2) Far fewer people have died in the industrialized states than in the stone age tribal societies
VI Parts of the book
A. Part I: 6-7 million years ago up to the agricultural revolution
(1) bones
(2) tools
(3) genes
B. Part II: Societal practices
(1) feeding of children past weening
(2) association of men and women into couples
(3) fathers and mothers caring for children
C. Part III: Our uniqueness and its precursors
(1) language
(2) art
(3) technology
(4) agriculture
D. Part IV: Our black traits and its precursors
(1) Xenophobic killing of other human groups
(2) Survey of world wide recorded history of xenophobic murder
(3) Destruction of environment and other animal species
E. Part V: Debunking a fantasy
(1) Destructive behavior occurred even before the
industrial revolution
(2) Our long history of environmental mismanagements
VII The Epilogue
(1) Traces the human species back to its ancestral origins and the
acceleration of our fall
VIII Purpose of the Book
(1) Help us not repeat our past mistakes
(1) Measure “Genetic Difference”
(2) Measure elapsed time since divergence
(3) Molecular Genetics along with Anthropology evidence is best
(4) Cladistics—Is the objective measurement using molecular genetics
II Human and chimp hypothetical question
(1) If it turned out that chimps were 99.9% similar to us, would it be ok to
lock them up in a cage?
III Characteristics and Relationships among primates
(1) Flat fingernails
(2) Opposable thumb
(3) Toenails
(4) Free hanging penis
Animal Primates
(1) The apes (gibbons, orangutans, gorillas, chimps)
(2) Monkeys
(3) Humans
Relationships
(1) Humans most similar to apes, and within the ape family we are
least similar to gibbons
IV More recent findings
(1) We are most closely related to the pygmy chimps (99.3%)
(2) We branched off earlier than chimps and gorillas did from each other
V History of molecular genetics
(1) Originated about 30 years ago
(2) Originally used by Sibley and Ahlquist in deciphering bird species
(3) Published results of seventeen hundred bird species
(4) Most scientist dismissed findings as ludicrous
VI Theory behind molecular genetics
(1) Look for certain chemicals that might provide a “clock” to measure
genetic differences
(2) DNA is that molecule
(3) After mixing different DNA, measure change in boiling point to determine the genetic difference
VII What is DNA?
(1) Replicating molecule
(2) The site at which transcription occurs
(3) Transcriptionàtranslationàprotein synthesis
Examples of proteins
(1) enzymes-lower activation energy for reactions
(2) hemoglobin-carry oxygen to cells
VIII Ethical Implications
(1) Testing of animals
(2) Caging of animals
Critical Review
A. Humans are most closely related to chimpanzees (99.3% identical to the pygmy
chimpanzee.
B. How can we be 99.3% identical and yet be so different
C. We would have liked a more detailed explanation on the methods employed by molecular geneticists to measure distance and difference.
Michael J. Mosbach
I. Six to Ten Million Years Ago – Major Changes Begun
A. A man-ape appeared that no longer used their hands to walk. They still did not walk upright or look human like.
B. Walking on two legs was first evident.
II. Three million years ago the man-ape evolved into to separate man-apes.
A. Australopithecus Robustus
1. A larger proto--human with a larger skull, and ate plant life.
B. Australopithecus Africanus
1. A thinner proto--human with a smaller skull, ate plant life and small animals.
III. Homo-habilis “Handyman”
A. Australopithecus Africanus Survived and developed into, “Homo-habilis” because of their ability to use wood and stone as crude tools.
B. Homo-erectus
C. About 1,700,00 years ago, an upright version of the homo-habilis is discovered.
1. It is possible that the homo-erectus aided in the extinction of the homo-habilis by eating them for food.
IV. Third Man?
A. Came from Australopithecus Africanus. Little known, did not survive long.
V. Homo-sapiens “Wise Man”
A. Appeared 500,000 years ago and looked more like humans today. Divided into three kinds of Homo-sapiens.
1. Neanderthals – Cave Men? No!
a. Occupied Europe.
b. Had large skulls protruding face, huge body and muscle strength.
c. Flourished from 130,00 years ago until about 40,00 years ago. In the 90,000 years of their existence, they used the exact same tool.
d. They know how to used fire regularly.
e. They did not have progress because they did not posses “innovation.”
f. Died between 30 and forty years of age.
g. They buried their dead.
2. Asians, (Peking Man) same evolution as Neanderthals
3. Anatomically correct Africans
a. Looked almost like we do today. Were smarter and finally evolved into Cro-Magnons
VI. Cro-Magnons – The Great Leap Forward
A. Appeared about 40,000 years ago.
B. Looked exactly like humans today.
C. Had INOVATION.
D. Created intricate tools for domestic use, built watercraft, made killing weapons for hunting at a safe distance (spears, bows and arrows)
E. Had jewelry, artwork, and music.
F. Lived about 60 years old, enabling passing of wisdom.
G. Increased functionality in vocal cords, tongue and associated muscles.
1. With increased voice functionality, language grew and sparked modern humanity.
2. Imagine the new found value of, “Turn left at the fourth tree and drive the male antelope toward the reddish boulder, where I’ll hide and spear it.”
Six to ten million years ago, there were major changes taking place within the ape species. Although apes move about using their hands and feet, a man ape that only used his feet appeared. A man-ape appeared that no longer used their hands to walk. They still did not walk upright or look human like.
Three million years ago the man-ape evolved into two separate man-ape species. The Australopithecus Robustus and the Australopithecus Africanus.
The Australopithecus Robustus was a larger proto--human with a larger skull, larger teeth and was known to eat plant life. The Australopithecus Africanus was a thinner proto--human with a smaller skull. He was known to eat small animals, as well as plant life. The Australopithecus Robustus did not survive.
The Australopithecus Africanus developed into what we know as the Homo-habilis (Handyman.) This proto--human was able to survive because of their implementation of crude tools made of wood and stone.
About 1,700,00 years ago, an upright version of the Homo-habilis is discovered, the Homo-erectus. Research suggests it is possible that the homo-erectus aided in the extinction of the homo-habilis by eating them for food. It is possible that a third proto-human, known as the third man, evolved from the Homo-habilis, however very little information is known about him. The homo-erectus was known for using another type of tools known as, fire! Although evidence shows fire in or around their excavations, it is doubtful that they were smart enough to start it themselves.
About 500,000 years ago, after the homo-erectus we find the first evidence of homo-sapiens (wise men.) Homo-sapiens were divided into three proto-humans. Neanderthals was the first. When we hear the name, we thing of cave men. Many were found in caves, however, that is simple because caves provided a shelter throughout the years to keep their excavations more intact. Neanderthals occupied Europe. They had large skulls, a protruding face, huge body and muscle strength. They knew how to used fire regularly, however they did not progress any further because they lacked the key ingredient that caused the great leap forward. They lacked innovation! They also had a lifespan of about 30 years. Even if they were capable of acquired wisdom, they would not live long enough pass it on. Oddly enough, they were known to burry their dead. Whether or not this had religious implications is a matter of debate. They flourished from 130,00 years ago until about 40,00 years ago. In the 90,000 years of their existence, they used the exact same tools as they started with. Anatomically correct Africans were the second to evolve from the homo-erectus. They looked almost like we do today. They were much smarter than the Neanderthals and finally evolved into Cro-Magnons. The anatomically correct Africans occupied much of the same areas that the Neanderthals did, and at the same time. There is no evidence that they mated with each other. Perhaps it is because they were simply not attracted to them, or maybe they tried but it was not genetically successful. The third homo-sapien to evolve from the homo-erectus was a proto-human found in China, known as the Peking Man. Little is known about this human except that he greatly resembled the Neanderthals of Europe.
The great leap forward began with the presence of the Cro-Magnons, which evolved from the anatomically correct Africans. They first appeared about 40,000 years ago, and looked exactly like humans today. These humans possessed innovation! They created intricate tools for domestic use, built watercraft, made weapons for hunting at a safe distance like spears, and bows and arrows. They wore jewelry, forged artwork, and created musical instruments. The key to the great leap was that cro-magnons showed an increase in the functionality of their vocal cords, tongue and associated muscles. They also had a life span of about 60 years. With longer life and increase voice functionality, language grew and sparked modern humanity. Things learned could be precisely communicated and past on from generation to generation. Imagine the new found value of, “Turn left at the fourth tree and drive the male antelope toward the reddish boulder, where I’ll hide and spear it.”
Critical Review
Summary
Chapter 7: Why Do We Grow Old and Die?
For centuries the search for eternal life, youth, and beauty has plagued humans. The quest for a “fountain of youth” has lead even modern day scientists to look into the causes of aging and death. What inherent quality do all humans and animals possess which makes them age and die?
“Why is it so easy to live to eighty, so hard to live to one hundred, and almost impossible to live to 120? Why do humans with access to the best medical care, and animals kept in a cage with plenty of food and no predators, inevitably grow infirm and die? It’s the most obvious feature of our life cycle, but there’s nothing obvious about what causes it.” (Diamond, Pg. 122)
Though all organisms age and die, humans have “improved considerably over the course of our evolutionary history.” Humans age more slowly than do our closest relative, the apes. The slow aging is a crucial part of our life cycle due to the dependence on information transmitted from one human to another. The survival of a whole clan could be dependent on the knowledge held by only one member over seventy, during the times of hunting and gathering. “Our long life span, therefore, was important for our rise from animal to human status.” (Diamond, Pg. 123) Our biology, then, evolved responding to the increased life expectancy.
The study on aging and dying can be attacked from two different angles, proximate explanations or ultimate explanations. The former explains the mechanism immediately responsible for the observation and the later explains the function or chain of events that lead to the mechanisms presence.
IE: “Why do skunks smell bad?” A proximate explanation may explain that the chemical compounds excreted by skunks possess a specific molecular structure, which results in bad smells. Therefore despite the function of the bad smell, the particular chemical compound will always smell bad. Evolutionary biologists respond with an ultimate explanation. The bad smell of skunks is a result of natural selection. To ward off would-be predators, skunks evolved to secrete bad-smelling chemicals. Those who smelled the worst, survived to produce more baby skunks.
A proximate explanation for aging examines the cellular mechanisms underlying aging, an ultimate explanation seeks to understand how natural selection would allow aging to occur. The proximate explanation is more elusive than the ultimate one, which evolutionary biologists think they have found.
It seems that the ultimate explanation in this case is irrelevant. Physiologists believe that something inherent in our physiology makes aging inevitable. One theory, attributes aging to the progressive difficulties faced by our immune system to differentiate our own cells from foreign cells. In other words, biological repair mechanisms fail to repair damaged or deteriorated cells.
Two types of repair occur in the body, damage control and regular replacement. An example of damage control is the repairing of DNA by enzymes that recognize and fix damaged DNA while ignoring intact DNA. Regular replacement can be explained by the constant growing of hair, no matter how short it is cut.
IE: To put it in lay-mans terms using cars as an analogy:
Damage control: Replacing a bumper only when it is dented, not at a regular service
Regular replacement: Changing the oil, air filter etc. in order to eliminate slight wear on the car before the car breaks down
The question that arises then, is Why don’t humans have unlimited repair capabilities? “There is nothing physiologically inevitable about the limited repair capabilities of us humans…Why for that matter, can’t we repair or replace everything in our bodies.” (Diamond, Pg. 126) The answer is, is it worth it. The expense of the repairs and the expected life span with and without the repairs determines how much should be invested. Natural Selection tends to maximize the production of offspring, so it can be said that that evolution is a strategy game in which the individual whose strategy leaves the most descendents wins.
“The problem of life span, and of investment in biological repair, is in turn one of an even broader class of evolutionary problems addressed by game theory: the mystery of what sets the maximum limit on any advantageous trait. “…:Natural Selection acts on whole individuals, not on single parts of an individual.” (Diamond, Pg. 127)
The strategy of evolution is to “optimize,” that is, each trait possessed by humans has been molded in order to maximize survival and reproductive success. So, instead of being too big or too small (which may make a particular trait the best it can be) the trait “converges on some optimal intermediate value, ” thereby making the whole human more successful and effective than if the trait was the best it could be. The importance of this is that this optimizes the energy of the being.
Why then did evolution make our life cycle so short? Wouldn’t we be more effective producers of offspring if our life cycles were longer? As said above, the expenditure of energy must be taken into consideration. Self-repair is constant, and though we cant re-grow limbs, we do continually replace and repair cells in our bodies. In addition to this, the risk of irreparable injury must be taken into account.
“…if an animal’s risk of death from irreparable accidents is low, then there is potential payoff, in the form of increased life span, from putting energy into expensive repair mechanisms that retard aging.” (Diamond, Pg. 131)
Lastly, gender plays a role. “we expect more potential payoff from repair mechanisms, and lower rates of aging, in that sex with the lower accidental mortality rate.” In the case of humans, men have a higher risk of irreparable injury due to fighting and bold displays.
“Correlated with this greater accidental death rate of men, men also age faster and have a higher non-accidental rate than women. At present, women’s life expectancy is about six greater than that of men…These differences suggest that evolution has programmed us so that women put more energy into self-repair, while men put more energy into fighting.” (Diamond, Pg. 133)
Finally, the puzzle in the case of women is that nature tends to program death to coincide with the end of fertility, and women live far past menopause. The answer Evolutionary biologists have come up with is that the energy that is spent in, and the danger posed by, childbirth threatens not only the mother, but the offspring as well. Therefore it benefits both to have a ceasing in fertility. This allows the woman to continue caring for her child without endangering her life with future pregnancies.
The above examples seek to explain the cause(s) of aging and dying. The progression then, as argued by evolutionary biologists is:
“There should not be just one, or even a few, dominant physiological mechanisms of aging. Instead, natural selection should act to match rates of aging in all physiological systems, with the result that aging involves innumerable simultaneous changes. The basis of this prediction is as follows. There’s no point in doing expensive maintenance on one piece of the body if other pieces are deteriorating more rapidly. Conversely, there’s no point in permitting a few systems to deteriorate long before all the others, because the cost of extra repairs on just those few systems would have bought big increase in life expectancy. Natural selection doesn’t make such pointless mistakes…thus, the optimal strategy for us, is to repair all parts of our [bodies] at rates such that everything finally collapses all at once.” “…this evolutionary ideal of simultaneous total collapse describes the fates of our bodies better than does physiologists’ long sought single Cause of Aging. (Diamond, Pg. 135-6)
Evolution seems indeed to have arranged things so that all our systems deteriorate, and that we invest in repair only as much as we are worth.
Ultimate evolutionary causation, he would have realized that natural selection would never permit us to deteriorate through a single mechanism with one simple cure.”
Outline
I. Introduction to the question
A. Why do we age and die?
I. The Approaches to the study of aging and dying
A. Proximate Explanation used by Biologists, Physiologists etc.
1. “the mechanism immediately responsible for the observation that [is] to be explained
ie: feces smell bad because of their chemical compound
: sugar tastes sweet because of its chemical compound
B. Ultimate Explanation used by Evolutionary Biologists
1. “the function or chain of events that caused that mechanism to be present
ie: feces smell bad to keep humans from thinking it is food
: sugar tastes sweet because it helps us determine when a food may supply optimal nutrition.
II. Progressive Difficulties faces by our Immune System
A. Suggested by Physiologists
1. Immune system can’t distinguish between the bodies cells and foreign cells.
III. Rebuttal By Evolutionary Biologists
A. Natural Selection would not make this mistake
1. Two types of repair mechanisms
a. Damage control
1. repairing or replacing damaged cells, tissues, etc.
ie: the body heals wounds to repair damage to the skin.
B. How does the body repair itself?
1. regular replacement
a. eliminate slight wear by replacing cells, tissues etc. before they are damaged
ie: humans go through two sets of teeth
2. Body has Limited repair capabilities
A. Why? Expense of Repairs to Body
1. Energy conservation
a. limited available to human body
ie: “how much an animal should invest in biological repairs depends on the expense of the repairs, and on a comparison of the animals expected life span with and without the repairs.”
B. Natural Selection maximized offspring production
1. Limited repair capabilities must be related
IV. Maximum limit on advantageous trait
A. “Optimize”
1. mole each trait to maximize survival and reproductive success
2. whole animal is successful
a. what combination of parts will optimize effectiveness
NOTE: this sets up the explanation of longevity as a trait that will be “optimized” or molded
V. Applying optimization to life cycle
A. Natural Selection adjusts to maximize reproductive output over lifetime
1. Adjusts relative expenditures of energy on repair and reproduction
NOTE: Does it benefit us to live longer? Would we reproduce more? Should we reproduce more?
B. Evolutionary Biologist Answers
1. Human Repair capabilities
a. Self-repair takes up energy
1. small amount left for other activities
a. Like caring for a baby
2. Irreparable Injury
a. risk of death from accidents
1. life span is increased if low
a. energy saved retards aging
3. Males and Females
A. Males have higher irreparable injury
1. Males life span shorter than women
VII Striking facts of aging become comprehensible
A. Women live past menopause despite natural selections programmed to coincide death with the end of fertility
1. Child care last decades
2. Children rely on mother for survival
3. Childbirth is dangerous to mother
4. Stopping childbirth capability protects both mother and child
VIII Conclusion
A. Our life span corresponds to energy used
B. “There is no point in permitting a few systems to deteriorate long before all others, because the cost of extra repairs on just those few systems would have bought a big increase in life expectancy
NOTE: There is more than one explanation for aging and death
Critical Review
(a) “Evolution seems indeed to have arranged things so that all our systems deteriorate, and that we invest in repair only as much as we are worth.” As an explanation for why humans age and die.
(b) The transitions from one idea to the next, the progression from one premise to the next to the conclusion is confusing. The many examples that he gives, although they are helpful with the concepts, make it difficult to follow the logic.
(c) All of the concepts were explained fully.