River out of Eden
Encyclopedia
River Out of Eden: A Darwinian View of Life is a 1995 popular science
book by Richard Dawkins
. The book is about Darwinian evolution
and includes summaries of the topics covered in his earlier books, The Selfish Gene
, The Extended Phenotype
and The Blind Watchmaker
. It is part of the Science Masters series
and is Dawkins' shortest book. It also includes illustrations by Lalla Ward
, Dawkins' wife. The book's name is derived from passage 2:10 of Genesis relating to the Garden of Eden
. The King James Version reads "And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads."
River Out of Eden comprises five chapters. The first chapter lays down the framework on which the rest of the book is built, that life is a river
of gene
s flowing through geological time where organism
s are mere temporary bodies. The second chapter shows how human ancestry can be traced via many gene pathways to different most recent common ancestor
s, with special emphasis on the African Eve
. The third chapter describes how gradual enhancement via natural selection is the only mechanism which can create the complexity we observe all around us in nature. The fourth chapter expounds on the utter indifference of genes towards organisms they build and discard, in their relentless drive to maximize their own utility functions. The last chapter summarizes milestones during the evolution of life on Earth
and speculates on how similar processes may work in alien
planetary system
s.
s that have ever lived: not a single one of our ancestors died before they reached adulthood and begot at least one child. In a world where most organisms die before they can procreate, descendants are common but ancestors are rare. But we can all claim an unbroken chain of successful ancestors all the way back to the first single-celled organism.
If the success of an organism is measured by its ability to survive and reproduce, then all living organisms can be said to have inherited good gene
s from successful ancestors instead of less successful contemporaries. Each generation
of organisms is a sieve against which replicated
and mutated
genes are tested. Good genes fall through the sieve into the next generation while bad genes are weeded out. This explains why organisms become better and better at whatever it takes to succeed, and is in stark contrast to Lamarckism
. Successful organisms do not and cannot refine their genes during their lifetime. Rather, good genes make successful organisms which perpetuate good genes themselves.
Following this gene-centered view of evolution
, it can be argued that an organism is no more than a temporary body in which a set of companion genes (actually alleles) cooperate toward a common goal: to grow the organism into adulthood, before they part company and go on their separate ways in bodies of the organism's progenies. Temporary bodies are created and discarded, but good genes live forever in the form of perfect replicas
of themselves, a result of high-fidelity copy process
which is typical of digital encoding
.
Through meiosis
(sexual reproduction
), immortal genes find themselves sharing temporary bodies with different set of intimate companion genes in successive generations of organisms. Thus genes can be said to flow in a river through geological time. Scoop up a bucket of genes from the river of genes, and we have an organism. Even though genes are selfish
, over the long run every gene needs to be compatible with all other genes in the gene pool
of a population
of organisms, in order to produce successful organisms.
A river of genes may fork into two branches, mostly due to the geographical separation between two populations of organisms. Because genes in the two branches never share the same bodies, they may drift
apart until genes from the two branches become incompatible. Organism created by these two branches (or two rivers) will form separate, non-interbreeding species
, completing the process of speciation
.
as generations are added to the lineage tree. In just 80 generations, the number of ancestors can exceed a trillion trillion.
This simple calculation does not take into account the fact that every marriage
is really a marriage between distant cousin
s which include second cousins, fourth cousins, sixteenth cousins and so on. The ancestry tree is not really a tree
, but a graph
.
A better way to model ancestry is to think in terms of genes flowing through a river of time. An ancestor gene flows down the river either as perfect replicas of itself or as slightly mutated descendant genes. Dawkins fails to explicitly contrast ancestor organism and descendant organisms against ancestor genes and descendant genes in this chapter. But the first half of the chapter is really about differences between these two models of lineage. While organisms have ancestry graphs and progeny graphs via sexual reproduction
, a gene has a single chain of ancestors and a tree of descendants.
Given any gene in the body of an organism, we can trace a single chain of ancestor organisms back in time, following the lineage of this one gene, as stated in the coalescent theory
. Because a typical organism is built from tens of thousands of genes, there are numerous ways to trace the ancestry of organisms using this mechanism. But all these inheritance pathways share one common feature. If we start with all humans alive in 1995 and trace their ancestry by one particular gene (actually a locus
), we find that the farther we move back in time, the smaller the number of ancestors become. The pool of ancestors continues to shrink until we find the most recent common ancestor
(MRCA) of all humans alive in 1995 via this particular gene pathway.
In theory, one can also trace human ancestry via a single chromosome, as a chromosome contains a set of genes and is passed down from parents to children via independent assortment from only one of the two parents. But genetic recombination
(chromosomal crossover
) mixes genes from non-sister chromatids from both parents during meiosis
, thus muddling the ancestry path.
However, the mitochondrial DNA
(mtDNA) is immune to sexual mixing, unlike the nuclear DNA
whose chromosomes are shuffled and recombined in Mendelian inheritance
. Mitochondrial DNA, therefore, can be used to trace matrilineal inheritance and to find the Mitochondrial Eve
(also known as the African Eve), the most recent common ancestor of all human via the mitochondrial DNA pathway.
. This chapter shows how the gradual, continuous and cumulative enhancement to organisms via natural selection
is the only mechanism which can explain the complexity we observe all around us in nature. Dawkins resolutely refutes the need of Creationists to invoke supernatural
powers in order to account for complexities. He refutes their "I cannot believe so and so could have evolved by natural selection" argument, calling it the Argument from Personal Incredulity.
Creationists often claim that some features of organisms (e.g. resemblance of Ophrys
(orchid) to female wasp, figure-eight dances
of honeybees, mimicry of stick insects, etc.) are too complicated to be a result of evolution. Some say, "half of an X will not work at all." Others say, "in order for X to work, it had to be perfect the first time." Dawkins shows that these are no more than bold assertions based on ignorance:
Dawkins goes on to illustrate his point by demonstrating how scientists have been able to fool creatures big and small using seemingly dumb triggers. For instance, stickleback
fish treat a pear-shaped as a sex bomb (a supernormal stimulus). Gulls' hard-wired instinct
s make them reach over and roll back not just their own stray eggs, but also wooden cylinders and cocoa tins. Honeybees push out their live and protesting companion from their hive, when the companion is painted with a drop of oleic acid
. Furthermore, a turkey will kill anything which moves in its nest unless it cries like a baby turkey. If the turkey is deaf, it will mercilessly kill its own babies.
An even more convincing way to refute the Argument from Personal Incredulity is to emphasize the gradual nature of evolution. For example, some creatures such as the stick insects possess the most amazing degree of camouflage
, but in fact any sort of camouflage is better than none. There is a gradient
from perfect camouflage to zero camouflage. A 100 percent camouflage is better than 99 percent. A 50 percent camouflage is better than 49 percent. A 1 percent camouflage is better than no camouflage. A creature with 1 percent better camouflage than its contemporaries will leave more descendants over time (an evolutionary success), and its good genes will come to dominate the gene pool.
Not only can we classify the degree of insect camouflage using a gradient, we can also study all aspects of the surrounding environment as gradients. For instance, a 1 percent camouflage may not be distinguishable from no camouflage under bright daylight. But as light fades and night sets in, there is a critical moment when the 1 percent camouflage helps an insect escape detection by its predator, while its companion with no camouflage is eaten. The same principle can be applied to the distance between prey and predator, to the angle of view, to the skill or the age of a creature, etc.
Not satisfied with merely demonstrating how gradual changes can bring about features as complex as the human eye
, Dawkins states that computer simulation
work by Swedish scientists Dan Nilsson and Susanne Pelger (although it is not a computer simulation but simple mathematical model) shows that the eye could have evolved from scratch a thousand times in succession in any animal lineage. In Dawkins' own words, "the time needed for the evolution of the eye... turned out to be too short for geologists to measure! It is a geological blink." And, "it is no wonder the eye has evolved at least forty times independently around the animal kingdom."
or, in other words, the purpose of life. This is the why question about life which philosophers and theologians have been pondering in vain for ages, and is a counterpart to the how question about nature which engineers have been able to resolve successfully.
Dawkins opens the chapter quoting how Charles Darwin
lost his faith in religion, "I cannot persuade myself that a beneficent
and omnipotent God
would have designedly created the Ichneumonidae
with the express intention of their feeding within the living bodies of Caterpillars." We ask why a caterpillar should suffer such cruel punishment. We ask why digger wasp
s couldn't first kill caterpillars to save them from a prolonged and agonizing torture. We ask why a child should die an untimely death. And we ask why we should all grow old
and die
.
Dawkins rephrases the word purpose in terms of what economists call a utility function, meaning "that which is maximized". Engineers often investigate the intended purpose (or utility function) of a piece of equipment using reverse engineering
. Dawkins uses this technique to reverse-engineer the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God.
According to Dawkins, it is a mistake to assume that an ecosystem
or a species
as a whole exists for a purpose. In fact, it is wrong to suppose that individual organisms lead a meaningful life either. In nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard. As hinted at in chapter one, genes are the supreme lords of the natural world. In other words, the unit of selection
is the gene, not an individual, or any other higher-order group as championed by proponents of group selection
.
As long as an organism survives its childhood and manages to reproduce thus passing its genes down to the next generation, what happens to the parent organism afterwards does not really bother genes. Because an organism is always at the danger of dying from accidents (a waste of investment), it pays for the genes to build an organism which pools almost all its resources to produce offspring as early as possible. Thus we accumulate damages to our body as we age and harbor late-onset diseases such as Huntington's disease
which have minimum impact on the evolutionary success of our gene overlords.
Genes are pitilessly indifferent to who or what gets hurt, so long as DNA is passed on. Dawkins wrote at the end:
. It seems that the trigger event would be the spontaneous arising of self-replicating entities or the phenomenon of heredity
. Once this process is initiated, it will launch an explosion of replicating entities until all available resources are used and all vacant niches are taken. Thus the title of the chapter.
Dawkins tries to distill ten milestones from the history of the only one replication bomb we know of, life on Earth. He strips any local conditions peculiar to Earth from these milestones which he calls thresholds, in the hope that these thresholds will be applicable to an alien evolution in an alien
planetary system
.
From the starting point of the Replicator Threshold, we may eventually reach the higher thresholds of Consciousness, Language, Technology, and Radio. The final threshold is Space Travel. In reaching the moon
, we have hardly made it past the front door.
Popular science
Popular science, sometimes called literature of science, is interpretation of science intended for a general audience. While science journalism focuses on recent scientific developments, popular science is broad-ranging, often written by scientists as well as journalists, and is presented in many...
book by Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
. The book is about Darwinian evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
and includes summaries of the topics covered in his earlier books, The Selfish Gene
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
, The Extended Phenotype
The Extended Phenotype
The Extended Phenotype is a biological concept introduced by Richard Dawkins in a 1982 book with the same title. The main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth, but extended to include all effects that a gene has on its...
and The Blind Watchmaker
The Blind Watchmaker
The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design is a 1986 book by Richard Dawkins in which he presents an explanation of, and argument for, the theory of evolution by means of natural selection. He also presents arguments to refute certain criticisms made on...
. It is part of the Science Masters series
Science Masters series
The Science Masters series is a global publishing venture consisting of original science books written by leading scientists and published by a worldwide team of twenty-six publishers assembled by John Brockman.Books include:...
and is Dawkins' shortest book. It also includes illustrations by Lalla Ward
Lalla Ward
Sarah Ward known as Lalla Ward, is an English actor, author and illustrator. As an actor, she is known for playing the part of Romana in the BBC science fiction television series Doctor Who. She is married to evolutionary biologist Richard Dawkins.-Early career:Ward's stage name, "Lalla", comes...
, Dawkins' wife. The book's name is derived from passage 2:10 of Genesis relating to the Garden of Eden
Garden of Eden
The Garden of Eden is in the Bible's Book of Genesis as being the place where the first man, Adam, and his wife, Eve, lived after they were created by God. Literally, the Bible speaks about a garden in Eden...
. The King James Version reads "And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads."
River Out of Eden comprises five chapters. The first chapter lays down the framework on which the rest of the book is built, that life is a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
of gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s flowing through geological time where organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s are mere temporary bodies. The second chapter shows how human ancestry can be traced via many gene pathways to different most recent common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
s, with special emphasis on the African Eve
Mitochondrial Eve
In the field of human genetics, Mitochondrial Eve refers to the matrilineal "MRCA" . In other words, she was the woman from whom all living humans today descend, on their mother's side, and through the mothers of those mothers and so on, back until all lines converge on one person...
. The third chapter describes how gradual enhancement via natural selection is the only mechanism which can create the complexity we observe all around us in nature. The fourth chapter expounds on the utter indifference of genes towards organisms they build and discard, in their relentless drive to maximize their own utility functions. The last chapter summarizes milestones during the evolution of life on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
and speculates on how similar processes may work in alien
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...
planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
s.
The digital river
Dawkins begins the book with a startling, yet true claim on behalf of all organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s that have ever lived: not a single one of our ancestors died before they reached adulthood and begot at least one child. In a world where most organisms die before they can procreate, descendants are common but ancestors are rare. But we can all claim an unbroken chain of successful ancestors all the way back to the first single-celled organism.
If the success of an organism is measured by its ability to survive and reproduce, then all living organisms can be said to have inherited good gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s from successful ancestors instead of less successful contemporaries. Each generation
Generation
Generation , also known as procreation in biological sciences, is the act of producing offspring....
of organisms is a sieve against which replicated
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
and mutated
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
genes are tested. Good genes fall through the sieve into the next generation while bad genes are weeded out. This explains why organisms become better and better at whatever it takes to succeed, and is in stark contrast to Lamarckism
Lamarckism
Lamarckism is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring . It is named after the French biologist Jean-Baptiste Lamarck , who incorporated the action of soft inheritance into his evolutionary theories...
. Successful organisms do not and cannot refine their genes during their lifetime. Rather, good genes make successful organisms which perpetuate good genes themselves.
Following this gene-centered view of evolution
Gene-centered view of evolution
The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...
, it can be argued that an organism is no more than a temporary body in which a set of companion genes (actually alleles) cooperate toward a common goal: to grow the organism into adulthood, before they part company and go on their separate ways in bodies of the organism's progenies. Temporary bodies are created and discarded, but good genes live forever in the form of perfect replicas
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
of themselves, a result of high-fidelity copy process
Copying
Copying is the duplication of information or an artifact based only on an instance of that information or artifact, and not using the process that originally generated it. With analog forms of information, copying is only possible to a limited degree of accuracy, which depends on the quality of the...
which is typical of digital encoding
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
.
Through meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
(sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
), immortal genes find themselves sharing temporary bodies with different set of intimate companion genes in successive generations of organisms. Thus genes can be said to flow in a river through geological time. Scoop up a bucket of genes from the river of genes, and we have an organism. Even though genes are selfish
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
, over the long run every gene needs to be compatible with all other genes in the gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
of a population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
of organisms, in order to produce successful organisms.
A river of genes may fork into two branches, mostly due to the geographical separation between two populations of organisms. Because genes in the two branches never share the same bodies, they may drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
apart until genes from the two branches become incompatible. Organism created by these two branches (or two rivers) will form separate, non-interbreeding species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, completing the process of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
.
All Africa and her progenies
When tracing human lineage back in time, most people look at parents, grandparents, great-grandparents and so on. The same approach is often taken when tracing descendants via children and grandchildren. Dawkins shows that this approach is misguided, as the numbers of ancestors and descendants seem to grow exponentiallyExponential growth
Exponential growth occurs when the growth rate of a mathematical function is proportional to the function's current value...
as generations are added to the lineage tree. In just 80 generations, the number of ancestors can exceed a trillion trillion.
This simple calculation does not take into account the fact that every marriage
Marriage
Marriage is a social union or legal contract between people that creates kinship. It is an institution in which interpersonal relationships, usually intimate and sexual, are acknowledged in a variety of ways, depending on the culture or subculture in which it is found...
is really a marriage between distant cousin
Cousin
In kinship terminology, a cousin is a relative with whom one shares one or more common ancestors. The term is rarely used when referring to a relative in one's immediate family where there is a more specific term . The term "blood relative" can be used synonymously and establishes the existence of...
s which include second cousins, fourth cousins, sixteenth cousins and so on. The ancestry tree is not really a tree
Tree (graph theory)
In mathematics, more specifically graph theory, a tree is an undirected graph in which any two vertices are connected by exactly one simple path. In other words, any connected graph without cycles is a tree...
, but a graph
Directed acyclic graph
In mathematics and computer science, a directed acyclic graph , is a directed graph with no directed cycles. That is, it is formed by a collection of vertices and directed edges, each edge connecting one vertex to another, such that there is no way to start at some vertex v and follow a sequence of...
.
A better way to model ancestry is to think in terms of genes flowing through a river of time. An ancestor gene flows down the river either as perfect replicas of itself or as slightly mutated descendant genes. Dawkins fails to explicitly contrast ancestor organism and descendant organisms against ancestor genes and descendant genes in this chapter. But the first half of the chapter is really about differences between these two models of lineage. While organisms have ancestry graphs and progeny graphs via sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
, a gene has a single chain of ancestors and a tree of descendants.
Given any gene in the body of an organism, we can trace a single chain of ancestor organisms back in time, following the lineage of this one gene, as stated in the coalescent theory
Coalescent theory
In genetics, coalescent theory is a retrospective model of population genetics. It attempts to trace all alleles of a gene shared by all members of a population to a single ancestral copy, known as the most recent common ancestor...
. Because a typical organism is built from tens of thousands of genes, there are numerous ways to trace the ancestry of organisms using this mechanism. But all these inheritance pathways share one common feature. If we start with all humans alive in 1995 and trace their ancestry by one particular gene (actually a locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
), we find that the farther we move back in time, the smaller the number of ancestors become. The pool of ancestors continues to shrink until we find the most recent common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
(MRCA) of all humans alive in 1995 via this particular gene pathway.
In theory, one can also trace human ancestry via a single chromosome, as a chromosome contains a set of genes and is passed down from parents to children via independent assortment from only one of the two parents. But genetic recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
(chromosomal crossover
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...
) mixes genes from non-sister chromatids from both parents during meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, thus muddling the ancestry path.
However, the mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
(mtDNA) is immune to sexual mixing, unlike the nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
whose chromosomes are shuffled and recombined in Mendelian inheritance
Mendelian inheritance
Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...
. Mitochondrial DNA, therefore, can be used to trace matrilineal inheritance and to find the Mitochondrial Eve
Mitochondrial Eve
In the field of human genetics, Mitochondrial Eve refers to the matrilineal "MRCA" . In other words, she was the woman from whom all living humans today descend, on their mother's side, and through the mothers of those mothers and so on, back until all lines converge on one person...
(also known as the African Eve), the most recent common ancestor of all human via the mitochondrial DNA pathway.
Do good by stealth
The main themes of the third chapter are borrowed from Dawkins' own book, The Blind WatchmakerThe Blind Watchmaker
The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design is a 1986 book by Richard Dawkins in which he presents an explanation of, and argument for, the theory of evolution by means of natural selection. He also presents arguments to refute certain criticisms made on...
. This chapter shows how the gradual, continuous and cumulative enhancement to organisms via natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
is the only mechanism which can explain the complexity we observe all around us in nature. Dawkins resolutely refutes the need of Creationists to invoke supernatural
Supernatural
The supernatural or is that which is not subject to the laws of nature, or more figuratively, that which is said to exist above and beyond nature...
powers in order to account for complexities. He refutes their "I cannot believe so and so could have evolved by natural selection" argument, calling it the Argument from Personal Incredulity.
Creationists often claim that some features of organisms (e.g. resemblance of Ophrys
Ophrys
The genus Ophrys is a large group of orchids from the alliance Orchis in the subtribe Orchidinae. There are many natural hybrids. The type species is Ophrys insectifera L.1753...
(orchid) to female wasp, figure-eight dances
Waggle dance
Waggle dance is a term used in beekeeping and ethology for a particular figure-eight dance of the honey bee. By performing this dance, successful foragers can share with their hive mates information about the direction and distance to patches of flowers yielding nectar and pollen, to water...
of honeybees, mimicry of stick insects, etc.) are too complicated to be a result of evolution. Some say, "half of an X will not work at all." Others say, "in order for X to work, it had to be perfect the first time." Dawkins shows that these are no more than bold assertions based on ignorance:
... Do you actually know the first thing about orchids, or wasps, or the eyes with which wasps look at females and orchids? What emboldens you to assert that wasps are so hard to fool that the orchid's resemblance would have to be perfect in all dimensions in order to work?
Dawkins goes on to illustrate his point by demonstrating how scientists have been able to fool creatures big and small using seemingly dumb triggers. For instance, stickleback
Stickleback
The Gasterosteidae are a family of fish including the sticklebacks. FishBase currently recognises sixteen species in the family, grouped in five genera. However several of the species have a number of recognised subspecies, and the taxonomy of the family is thought to be in need of revision...
fish treat a pear-shaped as a sex bomb (a supernormal stimulus). Gulls' hard-wired instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...
s make them reach over and roll back not just their own stray eggs, but also wooden cylinders and cocoa tins. Honeybees push out their live and protesting companion from their hive, when the companion is painted with a drop of oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...
. Furthermore, a turkey will kill anything which moves in its nest unless it cries like a baby turkey. If the turkey is deaf, it will mercilessly kill its own babies.
An even more convincing way to refute the Argument from Personal Incredulity is to emphasize the gradual nature of evolution. For example, some creatures such as the stick insects possess the most amazing degree of camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
, but in fact any sort of camouflage is better than none. There is a gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
from perfect camouflage to zero camouflage. A 100 percent camouflage is better than 99 percent. A 50 percent camouflage is better than 49 percent. A 1 percent camouflage is better than no camouflage. A creature with 1 percent better camouflage than its contemporaries will leave more descendants over time (an evolutionary success), and its good genes will come to dominate the gene pool.
Not only can we classify the degree of insect camouflage using a gradient, we can also study all aspects of the surrounding environment as gradients. For instance, a 1 percent camouflage may not be distinguishable from no camouflage under bright daylight. But as light fades and night sets in, there is a critical moment when the 1 percent camouflage helps an insect escape detection by its predator, while its companion with no camouflage is eaten. The same principle can be applied to the distance between prey and predator, to the angle of view, to the skill or the age of a creature, etc.
Not satisfied with merely demonstrating how gradual changes can bring about features as complex as the human eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, Dawkins states that computer simulation
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
work by Swedish scientists Dan Nilsson and Susanne Pelger (although it is not a computer simulation but simple mathematical model) shows that the eye could have evolved from scratch a thousand times in succession in any animal lineage. In Dawkins' own words, "the time needed for the evolution of the eye... turned out to be too short for geologists to measure! It is a geological blink." And, "it is no wonder the eye has evolved at least forty times independently around the animal kingdom."
God's utility function
This chapter explores the meaning of lifeMeaning of life
The meaning of life constitutes a philosophical question concerning the purpose and significance of life or existence in general. This concept can be expressed through a variety of related questions, such as "Why are we here?", "What is life all about?", and "What is the meaning of it all?" It has...
or, in other words, the purpose of life. This is the why question about life which philosophers and theologians have been pondering in vain for ages, and is a counterpart to the how question about nature which engineers have been able to resolve successfully.
Dawkins opens the chapter quoting how Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
lost his faith in religion, "I cannot persuade myself that a beneficent
Omnibenevolence
Omnibenevolence is defined by the Oxford English Dictionary as "unlimited or infinite benevolence". It is often held to be impossible, or at least improbable, for a deity to exhibit such property along side omniscience and omnipotence as a result of the problem of evil...
and omnipotent God
God
God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....
would have designedly created the Ichneumonidae
Ichneumonidae
Ichneumonidae is a family within the insect order Hymenoptera. Insects in this family are commonly called ichneumon wasps. Less exact terms are ichneumon flies , or scorpion wasps due to the extreme lengthening and curving of the abdomen...
with the express intention of their feeding within the living bodies of Caterpillars." We ask why a caterpillar should suffer such cruel punishment. We ask why digger wasp
Digger wasp
Wasps of the genus Sphex are cosmopolitan predators of the family Sphecidae that sting and paralyze prey insects. There are over 130 known digger wasp species. In preparation for egg laying, they construct a protected "nest" and then stock it with captured insects...
s couldn't first kill caterpillars to save them from a prolonged and agonizing torture. We ask why a child should die an untimely death. And we ask why we should all grow old
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
and die
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
.
Dawkins rephrases the word purpose in terms of what economists call a utility function, meaning "that which is maximized". Engineers often investigate the intended purpose (or utility function) of a piece of equipment using reverse engineering
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
. Dawkins uses this technique to reverse-engineer the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God.
According to Dawkins, it is a mistake to assume that an ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
or a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
as a whole exists for a purpose. In fact, it is wrong to suppose that individual organisms lead a meaningful life either. In nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard. As hinted at in chapter one, genes are the supreme lords of the natural world. In other words, the unit of selection
Unit of selection
A unit of selection is a biological entity within the hierarchy of biological organisation that is subject to natural selection...
is the gene, not an individual, or any other higher-order group as championed by proponents of group selection
Group selection
In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....
.
As long as an organism survives its childhood and manages to reproduce thus passing its genes down to the next generation, what happens to the parent organism afterwards does not really bother genes. Because an organism is always at the danger of dying from accidents (a waste of investment), it pays for the genes to build an organism which pools almost all its resources to produce offspring as early as possible. Thus we accumulate damages to our body as we age and harbor late-onset diseases such as Huntington's disease
Huntington's disease
Huntington's disease, chorea, or disorder , is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea...
which have minimum impact on the evolutionary success of our gene overlords.
Genes are pitilessly indifferent to who or what gets hurt, so long as DNA is passed on. Dawkins wrote at the end:
During the minute it takes me to compose this sentence, thousands of animals are being eaten alive; others are running for their lives, whimpering with fear; others are being slowly devoured from within by rasping parasites; thousands of all kinds are dying from starvation, thirst and disease. It must be so. If there is ever a time of plenty, this very fact will automatically lead to an increase in population until the natural state of starvation and misery is restored.
The replication bomb
In the last chapter, Dawkins considers how Darwinian evolution may look outside of planet EarthEarth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. It seems that the trigger event would be the spontaneous arising of self-replicating entities or the phenomenon of heredity
Heredity
Heredity is the passing of traits to offspring . This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent cell or organism. Through heredity, variations exhibited by individuals can accumulate and cause some species to evolve...
. Once this process is initiated, it will launch an explosion of replicating entities until all available resources are used and all vacant niches are taken. Thus the title of the chapter.
Dawkins tries to distill ten milestones from the history of the only one replication bomb we know of, life on Earth. He strips any local conditions peculiar to Earth from these milestones which he calls thresholds, in the hope that these thresholds will be applicable to an alien evolution in an alien
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...
planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
.
From the starting point of the Replicator Threshold, we may eventually reach the higher thresholds of Consciousness, Language, Technology, and Radio. The final threshold is Space Travel. In reaching the moon
Moon landing
A moon landing is the arrival of a spacecraft on the surface of the Moon. This includes both manned and unmanned missions. The first human-made object to reach the surface of the Moon was the Soviet Union's Luna 2 mission on 13 September 1959. The United States's Apollo 11 was the first manned...
, we have hardly made it past the front door.