Dunbar’s number

Dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individualknows who each person is and how each person relates to every other person.[1][2][3][4][5][6] This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found […]

Dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individualknows who each person is and how each person relates to every other person.[1][2][3][4][5][6] This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size.[7] By using the average human brain size and extrapolating from the results of primates, he proposed that humans can only comfortably maintain 150 stable relationships.[8] Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. It has been proposed to lie between 100 and 250, with a commonly used value of 150.[9][10] Dunbar’s number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.

Dunbar theorized that “this limit is a direct function of relative neocortex size, and that this in turn limits group size … the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained.” On the periphery, the number also includes past colleagues, such as high schoolfriends, with whom a person would want to reacquaint himself if they met again.[11]

Dunbar has argued that 150 would be the mean group size only for communities with a very high incentive to remain together. For a group of this size to remain cohesive, Dunbar speculated that as much as 42% of the group’s time would have to be devoted to social grooming. Correspondingly, only groups under intense survival pressure.

Dunbar, in Grooming, Gossip, and the Evolution of Language, proposes furthermore that language may have arisen as a “cheap” means of social grooming, allowing early humans to maintain social cohesion efficiently. Without language, Dunbar speculates, humans would have to expend nearly half their time on social grooming, which would have made productive, cooperative effort nearly impossible. Language may have allowed societies to remain cohesive, while reducing the need for physical and social intimacy.[12]

Dunbar’s number has since become of interest in anthropology, evolutionary psychology,[13] statistics, and business management. For example, developers of social software are interested in it, as they need to know the size of social networks their software needs to take into account; and in the modern military, operational psychologists seek such data to support or refute policies related to maintaining or improving unit cohesion and morale. A recent study has suggested that Dunbar’s number is applicable to online social networks[14][15] and communication networks (mobile phone).[16]

Philip Lieberman argues that since band societies of approximately 30-50 people are bounded by nutritional limitations to what group sizes can be fed without at least rudimentary agriculture, big human brains consuming more nutrients than ape brains, group sizes of approximately 150 cannot have been selected for in paleolithic humans.[20]Brains much smaller than human or even mammalian brains are also known to be able to support social relationships, including social insects with hierachies where each individual knows its place (such as the paper wasp with its societies of approximately 80 individuals [21]) and computer-simulated virtual autonomous agents with simple reaction programming emulating what is referred to in primatology as “ape politics”.[22]

Evolution

Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Despite their differences, evolution at both of these levels relies on the same, establish…

Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Despite their differences, evolution at both of these levels relies on the same, established mechanisms of evolutionary change:

Chimpanzee Genome Project

The Chimpanzee Genome Project is an effort to determine the DNA sequence of the Chimpanzee genome. It is expected that by comparing the genomes of humans and other apes, it will be possible to better understand what makes humans distinct from other species from a genetic perspective. Human and chimpanzee chromosomes are very similar. The […]

The Chimpanzee Genome Project is an effort to determine the DNA sequence of the Chimpanzee genome. It is expected that by comparing the genomes of humans and other apes, it will be possible to better understand what makes humans distinct from other species from a genetic perspective.

Human and chimpanzee chromosomes are very similar. The primary difference is that humans have one fewer pair of chromosomes than do other great apes. Humans have 23 pairs of chromosomes and other great apes have 24 pairs of chromosomes. In the human evolutionary lineage, two ancestral ape chromosomes fused at their telomeres, producing human chromosome 2.[3] There are nine other major chromosomal differences between chimpanzees and humans: chromosome segment inversions on human chromosomes 1, 4, 5, 9,12, 15, 16, 17, and 18. After the completion of the Human genome project, a common chimpanzee genome project was initiated. In December 2003, a preliminary analysis of 7600 genes shared between the two genomes confirmed that certain genes such as theforkhead-box P2 transcription factor, which is involved in speech development, are different in the human lineage. Several genes involved in hearing were also found to have changed during human evolution, suggesting selection involving human language-related behavior. Differences between individual humans and common chimpanzees are estimated to be about 10 times the typical difference between pairs of humans.[4]

About 600 genes have been identified that may have been undergoing strong positive selection in the human and chimp lineages; many of these genes are involved in immune system defense against microbial disease (example: granulysin is protective against Mycobacterium tuberculosis [8]) or are targeted receptors of pathogenic microorganisms (example: Glycophorin C and Plasmodium falciparum). By comparing human and chimp genes to the genes of other mammals, it has been found that genes coding fortranscription factors, such as forkhead-box P2 (FOXP2), have often evolved faster in the human relative to chimp; relatively small changes in these genes may account for the morphological differences between humans and chimps. A set of 348 transcription factor genes code for proteins with an average of about 50 percent more amino acid changes in the human lineage than in the chimp lineage.

Six human chromosomal regions were found that may have been under particularly strong and coordinated selection during the past 250,000 years. These regions contain at least one marker allele that seems unique to the human lineage while the entire chromosomal region shows lower than normal genetic variation. This pattern suggests that one or a few strongly selected genes in the chromosome region may have been preventing the random accumulation of neutral changes in other nearby genes. One such region on chromosome 7 contains the FOXP2 gene (mentioned above) and this region also includes the Cystic fibrosis transmembrane conductance regulator (CFTR) gene, which is important for ion transport in tissues such as the salt-secreting epithelium of sweat glands. Human mutations in the CFTR gene might be selected for as a way to survivecholera.[9]

Another such region on chromosome 4 may contain elements regulating the expression of a nearby protocadherin gene that may be important for brain development and function. Although changes in expression of genes that are expressed in the brain tend to be less than for other organs (such as liver) on average, gene expression changes in the brain have been more dramatic in the human lineage than in the chimp lineage.[10] This is consistent with the dramatic divergence of the unique pattern of human brain development seen in the human lineage compared to the ancestral great ape pattern. The protocadherin-beta gene cluster on chromosome 5 also shows evidence of possible positive selection.[11]

Results from the human and chimp genome analyses should help in understanding some human diseases. Humans appear to have lost a functional caspase-12 gene, which in other primates codes for an enzyme that may protect against Alzheimer’s disease.

The results of the chimpanzee genome project suggest that when ancestral chromosomes 2A and 2B fused to produce human chromosome 2, no genes were lost from the fused ends of 2A and 2B. At the site of fusion, there are approximately 150,000 base pairs of sequence not found in chimpanzee chromosomes 2A and 2B. Additional linked copies of the PGML/FOXD/CBWD genes exist elsewhere in the human genome, particularly near the p end of chromosome 9. This suggests that a copy of these genes may have been added to the end of the ancestral 2A or 2B prior to the fusion event. It remains to be determined if these inserted genes confer a selective advantage.

  • PGML. The phosphoglucomutase-like gene of human chromosome 2. This gene is incomplete and may not produce a functional transcript.[12]
  • FOXD. The forkhead box D4-like gene is an example of an intronless gene. The function of this gene is not known, but it may code for a transcription control protein.
  • CBWD. Cobalamin synthetase is a bacterial enzyme that makes vitamin B12. In the distant past, a common ancestor to mice and apes incorporated a copy of a cobalamin synthetase gene (see: Horizontal gene transfer). Humans are unusual in that they have several copies of cobalamin synthetase-like genes, including the one on chromosome 2. It remains to be determined what the function of these human cobalamin synthetase-like genes is. If these genes are involved in vitamin B12 metabolism, this could be relevant to human evolution. A major change in human development is greater post-natal brain growth than is observed in other apes. Vitamin B12is important for brain development, and vitamin B12 deficiency during brain development results in severe neurological defects in human children.
  • CXYorf1-like protein. Several transcripts of unknown function corresponding to this region have been isolated. This region is also present in the closely related chromosome 9p terminal region that contains copies of the PGML/FOXD/CBWD genes.
  • Many ribosomal protein L23a pseudogenes are scattered through the human genome.

humans are animals

The Moral Status of Animals First published Tue Jul 1, 2003; substantive revision Mon Sep 13, 2010 What is distinctive about humanity such that humans are thought to have moral status and non-humans do not? Providing an answer to this … Continue reading

The Moral Status of Animals
First published Tue Jul 1, 2003; substantive revision Mon Sep 13, 2010

What is distinctive about humanity such that humans are thought to have moral status and non-humans do not? Providing an answer to this question has become increasingly important among philosophers as well as those outside of philosophy who are interested in our treatment of non-human animals. For some, answering this question will enable us to better understand the nature of human beings and the proper scope of our moral obligations. Some argue that there is an answer that can distinguish humans from the rest of the natural world. Many of those who accept this answer are interested in justifying certain human practices towards non-humans—practices that cause pain, discomfort, suffering and death. This latter group expect that in answering the question in a particular way, humans will be justified in granting moral consideration to other humans that is neither required nor justified when considering non-human animals. In contrast to this view, many philosophers have argued that while humans are different in a variety of ways from each other and other animals, these differences do not provide a philosophical defense for denying non-human animals moral consideration. What the basis of moral consideration is and what it amounts to has been the source of much disagreement.

The species Homo sapiens share a genetic make-up and a distinctive physiology, but this is unimportant from the moral point of view. Species membership itself cannot support the view that members of one species, namely ours, deserve moral consideration that is not owed to members of other species. Humans are morally considerable because of the distinctively human capacities we possess. But which capacities are only human? There is no activity that is uncontroversially unique to humans. Both scholarly and popular work on animal behavior suggests that many of the activities that are thought to be distinct to humans occur in non-humans. Darwin brought us closer to the animal world, but equally brought animal nature closer to us. (http://plato.stanford.edu/entries/moral-animal/ ).

The notion of personhood identifies a category of morally considerable beings that is thought to be coextensive with humanity. Historically, Kant is the most noted defender of personhood as the quality that makes a being valuable and thus morally considerable. Yet Kant’s view of personhood cannot distinguish all and only humans as morally considerable. Some humans are not persons, i.e. infants, children, people with advanced forms of autism or Alzheimer’s disease or other cognitive disorders—do not have the rational, self-reflective capacities associated with personhood.

More to the point, rationality itself is suspect as a basis for moral right. On one hand, human rationality is bounded by lower level instincts and mechanistic behavior, and on the other, non-humans exhibit behavior that can be deemed moral. Thus morality is orthogonal to rationality. As a matter of fact, individuals that are hyper rational and lack lower level motional control of their behaviors are nor deemed highly moral, but rather are characterized as psychopathic (http://scienceblogs.com/cortex/2010/04/29/psychopaths-and-rational-moral/ ).

Al Dunlap [That would be “Chainsaw” Al Dunlap, former CEO of Sunbeam and notorious downsizer.] effortlessly turns the psychopath checklist into “Who Moved My Cheese?” Many items on the checklist he redefines into a manual of how to do well in capitalism. There was his reputation that he was a man who seemed to enjoy firing people, not to mention the stories from his first marriage — telling his first wife he wanted to know what human flesh tastes like, not going to his parents’ funerals. Then you realize that because of this dysfunctional capitalistic society we live in those things were positives. He was hailed and given high-powered jobs, and the more ruthlessly his administration behaved, the more his share price shot up.

Some models of human behavior in the social sciences assume that humans can be reasonably approximated or described as “rational” entities (see for example rational choice theory, or Downs Political Agency Models). Many economics models assume that people are on average rational, and can in large enough quantities be approximated to act according to their preferences. The concept of bounded rationality revises this assumption to account for the fact that perfectly rational decisions are often not feasible in practice because of the finite computational resources available for making them.

Bounded rationality is the idea that when individuals make decisions, their rationality is limited by the information they have, the cognitive limitations of their minds, and the time available to make the decision (http://en.wikipedia.org/wiki/Bounded_rationality ).

If morality is defined in terms of social behavior, non-humans exhibit different moral behavioral modes (http://www.ted.com/talks/frans_de_waal_do_animals_have_morals?%ca&language=en ). Social life may be regarded as a sort of symbiosis among individuals of the same species: a society is composed of a group of individuals belonging to the same species living within well-defined rules. When biologists interested in evolution theory first started examining social behavior, some apparently unanswerable questions arose, such as how the birth of sterile castes, like in bees, could be explained through an evolving mechanism that emphasizes the reproductive success of as many individuals as possible, or why, amongst animals living in small groups like squirrels, an individual would risk its own life to save the rest of the group. These behaviors may be examples of altruism. Revengeful behavior has been reported in non Homo sapiens (http://en.wikipedia.org/wiki/Ethology ).

Humans are animals in ways so subtly that we are unaware of it. Humans are subject to the same instinctual drives and influences as other animals are; it’s only human arrogance that would ever lead us to think otherwise. Fifty to seventy percent of the variation between individuals – in intelligence, in personality, in political leanings, or just about any other mental character you care to name – derives from the genes; zero to ten percent derives from the home environment; and the mysterious remainder is due to chance or to non-parental environment. (The Blank Slate: The Modern Denial of Human Nature by Steven Pinker)

The understanding that other people’s emotional states depend on the fulfillment of their intention is fundamentally important for responding adequately to others. Psychopathic patients show severe deficits in responding adequately to other people’s emotion. Psychopaths can teach us a lot about the nature of morality. At first glance, they seem to have perfectly functioning minds. Their working memory isn’t impaired, they have excellent language skills, and they don’t have reduced attention spans. In fact, a few studies have found that psychopaths have above-average IQs and reasoning abilities; their logic is impeccable. But the disorder is associated with a severe moral deficit. (http://scienceblogs.com/cortex/2010/04/29/psychopaths-and-rational-moral/ ).

So what’s gone wrong? Why are psychopaths so much more likely to use violence to achieve their goals? Why are they so overrepresented in our prisons? The answer turns us to the anatomy of morality in the mind. That’s because the intact intelligence of psychopaths conceals a devastating problem: the emotional parts of their brains are damaged, and this is what makes them dangerous.

When normal people are shown violent imagery or other painful stimulus, they automatically generate a visceral emotional reaction. Their hands start to sweat, and their blood pressure surges. But psychopaths feel nothing. When you peer inside the psychopathic brain, you can literally see this absence of emotion. After being exposed to fearful facial expressions, the emotional parts of the normal human brain show increased levels of activation. So do the cortical areas responsible for recognizing faces. As a result, a frightened face becomes a frightening sight; we naturally internalize the feelings of others. The brains of psychopaths, however, respond to these fearful faces with utter disinterest.

I am more inclined to take the position of Schopenhauer. For him, all individual animals, including humans, are essentially the same, being phenomenal manifestations of the one underlying Will. The word “will” designated, for him, force, power, impulse, energy, and desire; it is the closest word we have that can signify both the real essence of all external things and also our own direct, inner experience. Since everything is basically Will, then humans and animals are fundamentally the same and can recognize themselves in each other. For this reason, he claimed that a good person would have sympathy for animals, who are our fellow sufferers (http://en.wikipedia.org/wiki/Arthur_Schopenhauer ).

Schopenhauer emphasizes the necessity of finding a basis for Ethics that appeals, not to the intellect, but to the intuitive perception (http://en.wikisource.org/wiki/On_the_Basis_of_Morality/Translator%27s_Introduction ). According to Schopenhauer, the end of Ethics is not to treat of that which people ought to do (for ” ought ” has no place except in theological Morals, whether explicit, or implicit)

Group selection

Group selection is a proposed mechanism of evolution in which natural selection is imagined to act at the level of the group, instead of at the more conventional level of the individual. Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as […]

Group selection is a proposed mechanism of evolution in which natural selection is imagined to act at the level of the group, instead of at the more conventional level of the individual.

Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as groups.

From the mid 1960s, evolutionary biologists such as John Maynard Smith argued that natural selection acted primarily at the level of the individual. They argued on the basis of mathematical models that individuals would not altruistically sacrifice fitness for the sake of a group. They persuaded the majority of biologists that group selection did not occur, other than in special situations such as the haplodiploid social insects like honeybees (in the Hymenoptera), where kin selection was possible.

In 1994 David Sloan Wilson and Elliott Sober argued for multi-level selection, including group selection, on the grounds that groups, like individuals, could compete. In 2010 three authors including E. O. Wilson, known for his work on ants, again revisited the arguments for group selection, provoking a strong rebuttal from a large group of evolutionary biologists. As of yet, there is no clear consensus among biologists regarding the importance of group selection.

Metabolism

Metabolism (from Greek: μεταβολή metabolē, “change”) is the set of life-sustaining chemical transformations within the cells of living organisms. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to all chemical reactions that occur in living organisms, including digestionand the transport of […]

Metabolism (from Greek: ???????? metabol?, “change”) is the set of life-sustaining chemical transformations within the cells of living organisms. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to all chemical reactions that occur in living organisms, including digestionand the transport of substances into and between different cells, in which case the set of reactions within the cells is calledintermediary metabolism or intermediate metabolism.

Metabolism is usually divided into two categories: catabolism, the breaking down of organic matter by way of cellular respiration, andanabolism, the building up of components of cells such as proteins and nucleic acids. Usually, breaking down releases energy and building up consumes energy.

The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts that allow the reactions to proceed more rapidly. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell’s environment or to signals from other cells.

The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals.[1] The speed of metabolism, the metabolic rate, influences how much food an organism will require, and also affects how it is able to obtain that food.

A striking feature of metabolism is the similarity of the basic metabolic pathways and components between even vastly different species.[2] For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all known organisms, being found in species as diverse as the unicellular bacterium Escherichia coli and huge multicellular organisms like elephants.[3] These striking similarities in metabolic pathways are likely due to their early appearance in evolutionary history, and their retention because of their efficacy.

Phylogenetics

Phylogenetics /ˌfaɪloʊdʒəˈnɛtɪks, –lə–/[1][2] (Greek: φυλή, φῦλον – phylé, phylon = tribe, clan, race + γενετικός – genetikós = origin, source, birth)[3] – in biology – is the study of the evolutionary history and relationships among individuals or groups of organisms(e.g. species, or populations). These relationships are discovered through phylogenetic inference methods that evaluate observedheritable traits, […]

Phylogenetics /?fa?lo?d???n?t?ks, l?/[1][2] (Greek: ????, ????? – phylé, phylon = tribe, clan, race + ????????? – genetikós = origin, source, birth)[3] – in biology – is the study of the evolutionary history and relationships among individuals or groups of organisms(e.g. species, or populations). These relationships are discovered through phylogenetic inference methods that evaluate observedheritable traits, such as DNA sequences or morphology under a model of evolution of these traits. The result of these analyses is aphylogeny (also known as a phylogenetic tree) – a hypothesis about the history of evolutionary relationships.[4] The tips of a phylogenetic tree can be living organisms or fossils. Phylogenetic analyses have become central to understanding biodiversity, evolution, ecology, and genomes.

Taxonomy is the classification, identification and naming of organisms. It is usually richly informed by phylogenetics, but remains a methodologically and logically distinct discipline.[5] The degree to which taxonomies depend on phylogenies (or classification depends on evolutionary development) differs depending on the school of taxonomy: phenetics ignores phylogeny altogether, trying to represent the similarity between organisms instead; cladistics (phylogenetic systematics) tries to reproduce phylogeny in its classification without loss of information; evolutionary taxonomy tries to find a compromise between them.

Punctuated equilibrium

Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little net evolutionary change for most of their geological history. This state is calledstasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to […]

Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little net evolutionary change for most of their geological history. This state is calledstasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.[1] Punctuated equilibrium is commonly contrasted against phyletic gradualism, the belief that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous.

In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it punctuated equilibria.[2] Their paper built upon Ernst Mayr‘s model of geographic speciation,[3] I. Michael Lerner‘s theories of developmental and genetic homeostasis,[4] as well as their own empirical research.[5][6] Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of mostfossil species.

Stephen Jay Gould (/?u?ld/; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation.[1] Gould spent most of his career teaching at Harvard University and working at theAmerican Museum of Natural History in New York. In the later years of his life, Gould also taught biology and evolution at New York University.

Gould’s most significant contribution to evolutionary biology was the theory of punctuated equilibrium, which he developed with Niles Eldredge in 1972.[2] The theory proposes that most evolution is marked by long periods of evolutionary stability, which is punctuated by rare instances of branching evolution. The theory was contrasted against phyletic gradualism, the idea that evolutionary change is marked by a pattern of smooth and continuous change in the fossil record.

Most of Gould’s empirical research was based on the land snail genera Poecilozonites and Cerion. He also contributed to evolutionary developmental biology, and has received wide praise for his book Ontogeny and Phylogeny. In evolutionary theory he opposed strict selectionism, sociobiology as applied to humans, andevolutionary psychology. He campaigned against creationism and proposed that science and religion should be considered two distinct fields (or “magisteria“) whose authorities do not overlap.[3]

Gould was known by the general public mainly from his 300 popular essays in the magazine Natural History,[4] and his books written for a non-specialist audience. In April 2000, the US Library of Congress named him a “Living Legend“.[5]