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g. Species and Ecosystem Level Natural Selection Uncategorized

Species and Ecosystem Level Natural Selection

Species Level Natural Selection

Natural selection at species level relies on there being a geographical separation between groups within a species so that they can follow their own independent evolutionary path. Eventually, the genomes of two groups will become so different that they have difficulty interbreeding. For example, a male donkey and a female horse will produce a sterile mule. Ultimately, they will become separate “child” species and incapable of interbreeding. This process is known as speciation.

Population pressure among successful “child” species can cause them to migrate and come into contact with “sibling” species. There can only be one species in each ecological niche. If there are more, then competition for the niche will result in the fittest species, normally the migratory one, prospering and the least fit one becoming extinct. It is theoretically possible for this process to take place but, because millions of years would be required and there is, therefore, relatively little evidence of it, not all evolutionary biologists believe that it does. It may, however, have occurred among hominins.

Hominins are human-like species that evolved after our predecessors and those of the chimpanzees speciated between 12 and 5 million years ago. Since then, there are believed to have been 15 to 20 species of hominins, all of which, apart from our own, have become extinct. The migration of homo sapiens from Africa, where we originated, into Asia may have resulted in the demise of Homo Erectus, and our migration into Europe in the demise of the Neanderthals. Neanderthals were a sub-species, and some are known to have been subsumed by modern humans through interbreeding. This is confirmed by the existence of part of the Neanderthal genome in non-African branches of our species. However, most were probably outcompeted by modern humans. It is unclear whether Homo Erectus was an entirely separate species and became extinct or whether it too was subsumed in a similar way.

Presently, it is difficult to identify any behavioural traits which may have evolved in modern humans as a result of species level selection as this would require a comparison with other, now extinct, hominin species.

Ecosystem Level Natural Selection

The final level in the organisation of life comprises the world’s ecosystems. These are the final, and largest, Russian dolls on which individual organisms depend for their survival and ability to procreate.

A natural ecosystem comprises all the non-living ingredients for life, e.g., a source of energy, water, minerals, atmospheric gases and so on. It also comprises numerous species, each of which has its own niche or role to play, and each of which interacts with other species to form a complex system. Each ecosystem is adapted to its own habitat, and these can be highly variable to include, for example, freshwater, marine, tropical, mountainous, and desert habitats.

The roles played by species are classified using the food chain. Generally, there are only up to 4 or 5 levels, which typically comprise:

  1. Producers: organisms that produce food for all other species in the ecosystem, e.g., green plants which convert inorganic substances into organic material through photosynthesis.
  2. Primary consumers or herbivores: animals that consume plants, e.g., sheep and goats.
  3. Secondary consumers or carnivores: animals that feed on others, e.g., the big cats and sharks.
  4. Tertiary Consumers. These are also carnivores but ones that consume other carnivores, e.g., polar bears and crocodiles.
  5. Decomposers: organisms which feed on dead organic material and help in the recycling of nutrients, e.g., fungi and earthworms.

The flow of energy in a natural ecosystem is largely unidirectional. Plants, which take their energy from sunlight, were the first to evolve and altered the environment, thereby permitting the evolution of herbivores, which take their energy from plants, followed by carnivores, which take their energy from herbivores.

Some species do not fit neatly into these classes. For example, humans are omnivorous, consuming both animals and plants. There are also parasites which feed on a living host. Nevertheless, the above classification is a helpful guide.

All levels of natural selection exist within an ecosystem: individual, kin, group, and species. However, for ecosystem level selection to be possible, there must be more than one ecosystem competing to control the same habitat. This is not apparent in the natural world. Rather, it appears to have been introduced by mankind, as will be discussed in the next post.

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f. The Influence of Group Level Natural Selection on Humanity Uncategorized

The Influence of Group Level Natural Selection on Humanity

One of the main criticisms of group level natural selection has been that we know relatively few examples in which group behaviour has led to biological evolution. However, among them is one now regarded as being a rare and significant evolutionary transition: the evolution of the human brain. Another objection has been that groups reproduce and die off at a far slower rate than individuals and, thus, biological evolution driven by group behaviour will take place at a similarly slow rate. However, this is contradicted by the relatively rapid evolution of our brain.

The human brain differs from that of our ancestors not only in size but also in attitudes and skills. Examples of the latter include our relative Finally, Wilson, Timmel and Miller, in their study of cognitive co-operation found that groups perform better at problem solving tasks than individuals, and that the gap increases with the difficulty of the task. In other words, groups perform better than individuals when solving complex problems.

Large brains consume a great deal of energy, approximately 20% in humans. Their growth probably began approximately 2.6 million years ago, when our previously vegetarian ancestors shifted to a higher reliance on meat. At the same time, it became more efficient to occupy a campsite and send out hunters than for the entire tribe to hunt. In return, the hunters benefitted from the protection of the campsite in which their young were raised. Family based social groups did exist prior to the shift to meat eating but the changes brought about by meat consumption began a process of increasing co-operation between families, initiating a shift to less kin-reliant groups.

An important factor in whether a group forms is its ability to benefit its members. Unlike kin selection, each member requires reassurance that the others have a similar outlook and takes their reciprocal support as evidence. Co-operation requires the individual to have an understanding of other group members and their motives together with considerable negotiating skills. It also requires an ability to recognise exploitation of the group by individual members; this necessitates moral systems, and processes for dealing with intransigence. It is important to mention that competition between individual group members and families is not extinguished but merely suppressed.

Within groups a culture develops comprising several memes, i.e., agreed values, norms, beliefs, and symbols. Values are those things that we hold “good”, norms are forms of behaviour expected from group members, beliefs those things that we hold true, and symbols are ceremonies, ornamentation, etc., which identify us as being members of the group. Memes are subject to a process like that of gene selection. They will survive and propagate if they are fit for their environment or fall into disuse if they are not. It is not necessary, however, for a group to become extinct for a culture to expire. Nor is a culture necessarily linked to an ethnic group as multi-ethnic cultures are also possible.

Culture propagates from generation to generation but, unlike biological inheritance, it can also propagate from group to group through social learning. If a culture is successful, it can be transferred by imitataion or by coercion. Thus, cultural evolution takes place through the exchange of ideas and practices, with the most successful cultures surviving and propagating whilst the less successful ones expire. This process is far more rapid and adaptive to changing circumstances than biological evolution. Significant changes can occur within a few generations or less. This has, for example, allowed us to populate different environmental niches, from the arctic to the desert.

The evolution of our large brains has been very rapid and is thought to have been brought about by a process of positive feedback between cultural evolution and biological evolution with the former taking the lead. As groups became more complex and effective, they needed the greater skills and pro-social tendencies provided by larger brains. These, in turn, enabled groups to become yet more complex and effective. Because groups that co-operated well were more successful than those that did not, the individuals with the brains, skills, and attitudes needed to facilitate this were subject to natural selection and, thus, came to predominate. Although this process is speculative, mathematical modelling by Luke Rendell et al., of the University of St. Andrews, has shown it to be capable of producing strong selection pressures and the rapid evolution of biological traits.

Successful group co-operation relies on individuals knowing one another and limits on an organism’s ability to do so mean that there is a maximum group size which varies from species to species. In the 1990s, the anthropologist and evolutionary psychologist, Robin Dunbar, found a correlation, in primates, between brain size and social group size. From this he proposed a maximum social group size for humans of about 150.

In the last 5000 years, human society has become more complex. It now comprises numerous inter-dependent groups, each with its own specific purpose. They are not necessarily kin groups and are often based entirely on mutual co-operation. Some even prohibit nepotism. Most of us now occupy cities whose populations can be in the tens of millions. Cities are co-operative groups on a very large scale. We even describe them as organisms, using phrases such as “the beating heart” or “the veins and arteries”. There is no doubt that urbanisation, and the greater specialisation and co-operation that it brings, have resulted in an explosion in our population. Although this is probably a result of cultural evolution, in time, biological adaptations may follow.

Most of the changes arising from group behaviour that we can observe This raises many questions about our future, of course, such as “Is the process accelerating?” and “Where will it ultimately lead?”.

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e. Group Level Natural Selection

Group Level Natural Selection

There has been much academic debate between evolutionary biologists, such as John Maynard Smith, W. D. Hamilton, George C. Williams, and Richard Dawkins, who advocate individual level selection plus rare cases of kin selection, and others, such as David Sloan Wilson, Elliott Sober and E.O. Wilson, who advocate multi-level selection. However, a consensus is beginning to emerge that a process of natural selection occurs at each biological level, i.e.: the genome, cell, organism, family, group, species, and ecosystem. Due to emergent properties, i.e., properties held by systems which are not held by their component parts, the process of natural selection at each level can differ. However, the process at each level tends to be undermined by stronger selection processes at lower levels.

E.O. Wilson described multi-level selection using the analogy of Russian dolls. The various biological levels can be likened to nested containers for competing genes. To varying degrees, the genes rely on each container for their survival and propagation. Thus, higher level selection can be a significant factor in some species and has probably played a part in human evolution.

Selection at cell level does occur within an organism. For example, recent research has shown that, in certain circumstances, cancer cells can evolve from healthy cells under pressure from the organism’s immune system. However, this form of evolution is normally a dead end. The cells act together to form the organism which is a container that they rely on for their continued existence. There may be billions of cells acting together over thousands of cell generations. However, evolution has shaped their genome to behave altruistically and, ultimately, the vast majority die out with the organism. Typically, only two or three carry the organism’s genes forward through reproduction. Thus, natural selection operates at the level of the organism rather than at the level of the cell.

Group selection forms part of the theory of multi-level selection. It is a natural selection process whereby traits evolve due to the fitness of a group of organisms, who are not necessarily kin, to their environment. The theory of group level natural selection proposes that groups which co-operate are more likely to be successful than those which do not. An individual will see it as beneficial to its own survival and ability to reproduce if it supports the group through co-operation. The concept has a long history. Darwin wrote on how groups can, but do not necessarily, evolve into adaptive units. This view was generally accepted until the mid-1960s. It was then criticised in favour of the view that evolution was based solely on the fitness of the individual. However, with advances in the science of multi-level selection, it is now returning to acceptability.

Both kin selection and group selection have, in a complex and inter-related way, had a part to play in governing human evolution. Kin selection has had a stronger influence on us than group selection. We will, for example, tend to favour a brother over an unrelated colleague. However, it is not the only factor which has determined our social behaviour. Charles Goodnight, in comparing the two, concludes that kin selection and multi-level selection should be considered complementary approaches which, when used together, give a clearer picture of our evolution than either can alone.

Together, kin and group selection explain some of the moral dilemmas that we face and how we handle them. There is often a conflict between the immediate interest of the individual, those of the individual’s kin, and the interests of the individual and its kin via the group. These interests, all of which are inherited, manifest themselves both in the form of competition between members of a group, and in the form of competition between groups. The individual must balance individual level competition and group level co-operation in a way which optimises their survival and the propagation of their genes. The way that we do so is explained by Freud’s model of the human psyche, i.e., the id, which is concerned with immediate personal interest, the super-ego which is concerned with group interest, and the ego which moderates between the two. However, because group selection is relatively recent, the super-ego is probably an inherited pre-disposition whose detailed contents are acquired through social learning. Freud’s model is relatively universal in human beings and is probably an innate consequence of multi-level selection, therefore.

Politics provides another example which demonstrates the existence of multi-level selection in humanity. The ideology of right-wing parties is one of individualism whilst that of left-wing parties is one of collectivism. Thus, we have the same dilemma in our political institutions both at a national level and at international level. Multi-level selection pervades humanity, therefore, from our individual psyche to our highest institutions.

In my next post I will give further examples of the influence of kin and group level natural selection on humanity.

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d. Kin Level Natural Selection Uncategorized

Kin Level Natural Selection

An early precursor to kin selection was the theory of inclusive fitness. This was proposed by J.B.S. Haldane in 1932 but developed and named by William Donald Hamilton in 1964. Hamilton’s theory is the basis of Richard Dawkins famous book, “The Selfish Gene” and argues that it is the survival and reproduction of genes, rather than organisms, that is the principal driver behind evolution. As a result, an organism can display altruism if this leads to a greater propagation of the genes it holds than would be the case if it acted solely out of personal self-interest. This relies on the individual organism being able to identify those genes in others. There are two main ways of doing so. Firstly, by knowing its kin or related family members and, secondly, by recognising external characteristics displayed by others with the relevant gene. However, there are several difficulties with the latter, for example whether the gene does in fact express itself in the form of recognisable traits and whether the organism can see those traits. Because such traits are often only skin deep, there is the potential for imposters to display them to benefit from altruistic behaviour.

The more specific theory of kin selection developed from Hamilton’s work. This theory states that an organism can behave in a way which maximises the propagation of its genes by behaving in an altruistic manner towards close relatives likely to hold the same genes.

Individuals in a species have approximately 99% of their genes in common. The remaining 1% constitutes their variable genome which accounts for physical variation within the species. The fitness of the 99% is well established and, thus, only genes in the variable genome, including any mutations, compete to propagate themselves. 50% of the variable genome is inherited from each parent. On average, therefore, an individual will share 50% with each parent, child, and sibling and, on average, 25% with each grandparent, uncle, aunt, nephew, niece, or grandchild. The theory of kin selection proposes, therefore, that it is advantageous in terms of the propagation of the variable genome to favour the survival and reproduction of three siblings over that of the self. Thus, genetically driven behaviour which facilitates this will propagate within the species.

Kin selection behaviour relies on the ability of an individual to recognise its kin. Nurture kinship, i.e., having raised, been raised by, or having been raised with another nuclear family member, is clearly an important factor, and can be observed in other species. However, the recognition of more remotely related kin, e.g., aunts, uncles, and other members of the extended family, requires considerable cognitive skill and, so, is probably limited to the more intelligent species.

As individuals become more remotely related, it only becomes possible to recognise kinship through physical appearance and, in the case of humans, cues such as language, dress, beliefs, etc. Thus, kin selection suggests that an individual is more likely to behave altruistically towards others of similar appearance and culture because these factors also suggest a similar variable genome.

Intuitively, kin selection operates within humanity. There is also a great deal of objective evidence for its presence. For example, research has shown that non-reciprocal help is far more likely to occur in kin relationships than non-kin relationships. It has also been shown that, when wills are written, there is a close correlation between kinship and the proportion of wealth passed on.

A small number of species can be described as eusocial. These species co-operatively rear their young across multiple generations. They also divide labour through the surrender, by some members, of all or part of their personal reproductive success to increase the reproductive success of others. In this way they benefit the overall reproductive success of the group. Eusociality arose late in the history of life and is extremely rare. Only nineteen species are known to display this characteristic: two species of mole rat, some species of brine shrimp, insects such as wasps, bees, and ants and, of course, mankind. In eusocial species, group level natural selection takes place due to competition between groups. In the case of the eusocial insects, the group is the nest or hive. Individual workers will lose their lives in the interest of the hive as a whole. It can be argued that this form of behaviour in insects is entirely altruistic and an inherited form of kin selection. However, in the case of humanity, this argument does not hold true because human groups display both kin altruism and non-kin co-operation.

However, there remain doubts whether individual and kin selection fully explain natural selection and human social behaviour since natural selection may also occur at higher biological levels. This will be explored further in subsequent posts.

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c. Individual Level Natural Selection

Individual Level Natural Selection

An understanding of natural selection is important to dispel the myth of Social Darwinism. This unfortunately named myth, which flourished in the late 19 and early 20th Centuries, was applied to human society. It held that the strong prosper whilst the weak founder.

Natural selection may occur at several biological levels: the level of the individual organism; the level of the kin group, i.e., a family of organisms related through reproduction; the level of the social group; at species level, or even at ecosystem level. These biological levels form a hierarchy with individual organisms at the bottom and ecosystems at the top.

Selection at each of these levels can be understood as competition between organisms, kin groups, social groups, species, or ecosystems for the resources in a particular environment. The one which best fits that environment is the one which will survive, propagate and, ultimately, predominate.

There are two main theories of natural selection. Firstly, that selection only occurs at the individual and kin levels. Secondly, that selection occurs at multiple levels. All theories accept that natural selection occurs primarily at the level of the individual organism, but opinions differ over whether it can also occur at higher biological levels and where the cut-off point is as we rise up through those levels.

Because the subject is complex, it will be split over five posts, one for each biological level beginning with individual level selection.

Darwin believed that natural selection occurred primarily at the level of the individual organism, i.e., that a trait in an individual organism which made it fitter in the context of its environment would enable it to survive and reproduce better than others without that trait.

An organism’s environment comprises not only the physical world but also other members of its own species and members of other species. This can lead to more complex selection processes such as sexual selection and co-evolution. These processes take place at the level of the individual organism, nevertheless.

Sexual selection can occur in organisms which reproduce sexually. Generally, partners in procreation are chosen based on their appearance of health and success. This appearance suggests that they do not carry adverse genes which may prejudice the survival of any joint offspring. In many species this has led to the evolution of traits which overtly demonstrate health and success, for example the plumage of birds. Clearly, successful partner selection will propagate the genes on which an organism relies for its survival and will eventually become a species trait, therefore.

There are, of course, many other traits and ways of displaying them which improve an organism’s likelihood of mating, an example is the support that one parent provides for the other while offspring are being reared.

The environment of any species includes other species with which it interacts. Thus, new traits in one species can evolve in response to new traits in another and vice versa. This effect is known as co-evolution, a concept first proposed by ecologists P.R. Erlich and P.H.Raven in 1964. One example is the evolutionary arms race between a predator, in the form of improving predatory skills, and its prey, in the form of increasing ability to avoid predation. Similarly, a plant and its pollinator can co-evolve traits to the point that there is a clear interdependence between the two species. Examples of co-evolution are widespread in all natural ecosystems.

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b. Basic Theory of Evolution

The Basic Theory of Evolution

Mankind is a consequence of evolution through a combination of random mutation and natural selection. Charles Darwin first postulated this process in 1858 and published it in his 1859 book “On the Origin of Species”. At the time, DNA and its role had not been discovered and Darwin referred to a more general principle of inheritance. DNA was first discovered in the 1860s by the Swiss chemist Johann Friedrich Miescher but its central role in the evolutionary process was not understood for almost a century thereafter. In the early 1950s Rosalind Franklin produced an Xray photograph of DNA which, in 1953, enabled James Watson and Francis Crick to discover its double helix structure. This in turn enabled them to explain how it carries and replicates genetic information. Since that time, a substantial amount of scientific evidence has accumulated in support of Darwin’s theory.

An organism’s genes are sequences in its DNA which either directly or indirectly enable the manufacture of molecules whose function determines the organism’s characteristics. These characteristics, in turn, determine the organism’s ability to survive and reproduce within its environment.

Random mutations are changes in the DNA sequence and, thus, in the organism’s genes.  They are an example of the impact of entropy on life. They can be caused by errors in DNA replication, by exposure to damaging chemicals, by exposure to radiation or by the insertion or deletion of segments by mobile genetic elements such as viruses. Mutations are entirely random and are not in any way pre-determined to benefit the organism. Most mutations (about 70%) are, in fact, harmful and the remainder either neutral or weakly beneficial.

Natural selection means that organisms with hereditary characteristics most suited to their environment, i.e., the fittest, are most likely to survive and reproduce. Organisms which are poorly adapted to their environment are less likely to do so. Thus, the genes of the fittest organisms are those most likely to be passed on to offspring, to propagate through the population and, thus, predominate. It is through this selection process that life resists entropy.

It is important to note that mutations are not a consequence of changes in the environment. Rather, they pre-exist within a species’ variable genome and cause diversity in its population. When, the environment changes, most of a population may find itself unfit and die off. However, a small proportion carrying certain mutations may find itself to be fitter in the new circumstances and may, therefore, survive and propagate more successfully than it had in the past.

Most evolutionary biologists agree that, for the majority of species, natural selection operates at the level of the individual organism, i.e., inherited characteristics will cause the organism to behave in a way which maximises its own, and only its own, chances of survival and reproduction. However, there are a small number of species in which individuals display what has been referred to as “altruism”. That is, they will suffer a degree of disadvantage to their own survival and ability to reproduce to improve that of other members of their species. This has given rise to a number of competing theories of natural selection that I will discuss in my next post. However, before moving on to that topic, I would like to mention three important points.

Firstly, there is a difference between the meanings of “altruism” and “co-operation”. When an individual behaves altruistically, it acts in a manner which benefits the survival and reproductive chances of some other individual or individuals. This may disadvantage the former and there is not necessarily a payback. However, when an individual behaves co-operatively there is a payback. This is a subtle difference but of great significance in evolutionary theory. Do the small number of species referred to above behave altruistically or do they behave co-operatively? If the latter, then what is the payback?

Secondly, human beings differ from other species in several important ways. We have large brains with highly advanced cognitive skills which, among other benefits, enable us to identify opportunities and risks and to predict outcomes. We are also social animals and form groups. These groups have diverse cultures, i.e., ways of organising themselves, and we pass aspects of our cultures from one generation to another and from one group to another through social learning.

Finally, as systems grow ever more complex, they display emergent properties, i.e., properties of the system which are not held by its individual parts. Life is a collection of systems of increasing complexity, e.g., cells, multi-cellular organisms, groups of organisms, species, and eco-systems. As the level of complexity increases it can be expected that system properties will emerge. Thus, it is not necessarily the case that a property governing natural election at the cellular level will be the only property governing it at more complex levels. Other, emergent properties may come into play.

Natural selection, particularly in the case of human beings, is not a straightforward process therefore as will be discussed in my next post.