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Jan

2012

Richard Dawkins, "Replicators and Vehicles" 1982

www.stephenjaygould.org/...dawkins_replicators.html

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dawkins replicators genes evolution selection

What are DNA molecules for?
Living matter is nested in a hierarchy of levels
38 more annotation(s)...
- the dispute between individual and group is different in kind from the dispute between individual and gene.
- what we ought to mean
- most effective
- there are two ways in which we can characterize natural selection. Both are correct; they simply focus on different aspects of the same process.
- any entity in the universe of which copies are made
- A germ-line replicator, as distinct from a dead-end replicator
- an active, as distinct from a passive, replicator is a replicator that has some causal influence on its own probability of being propagated.
- When we say that an adaptation is "for the good of' something, what is that something? Is it the species, the group, the individual, or what? I am suggesting that the appropriate "something," the "unit of selection" in that sense, is the active germ-line replicator.
- It is their phenotypic effects that are the proximal subjects of selection
- Natural selection, of course, depends on the variation
- replicators may therefore be regarded as in competition with other replicators.
- each replicator is a competitor specifically of its alleles at its own locus on the chromosomes of the population
- that which segregates and recombines with appreciable frequency"
- a unit that is potentially immortal (Dawkins, 1976, chapter 3), a point I learned from Williams (1966). Briefly, the rationale is that an entity must have a low rate of spontaneous, endogenous change, if the selective advantage of its phenotypic effects over those of rival ("allelic") entities is to have any significant evolutionary effect.
- The asexual organism's genome may be considered a replicator, since any alteration in it tends to be preserved.
- there is a hierarchy of nested vehicles
- cell organelles, haploid organisms, and gametes are levels of selection with a higher heritability than diploid sexual genotypes, since the latter do not perfectly reproduce themselves, but undergo segregation and recombination in the course of their reproduction
- replicators are not directly visible to natural selection
- literally indivisibility-being sufficiently heterogeneous in form to be rendered nonfunctional if cut in half)
- in nature behaves as if it had a single purpose
- "The 'ramet' is the unit of clonal growth, the module that may often follow an independent existence if severed from the parent plant"
- The "genet," on the other hand, is the unit that springs from one single-celled zygote, the "individual" in the normal zoologists' sense.
- Each new vehicle comes into being through an act of reproduction. New parts of vehicles come into being through growth.
- In order to make complex adaptations at the level of multicellular organs—eyes, ears, hearts, etc.—a complex developmental process is necessary.
- given that death and reproduction do occur in a lineage, evolution in that lineage becomes possible
- reproduction as the process by which a new vehicle comes into existence, and growth as the process by which an existing vehicle develops
- genetic mosaics
- The whole "plant" would not function as a vehicle propagating the genes inside it, because different cells inside it would contain different genes. Cells would function as vehicles, and adaptations would not be for the good of the whole plant but for the good of smaller units within the plant. To qualify as a "vehicle," an entity must come into being by reproduction, not by growth.
- Groups do not go through a regular cycle of growth (development), alternating with "reproduction" (sending off a small "propagule" which eventually grows into a new group).
- "group selection" in the sense of D. S. Wilson (1980) can only work if there is some mechanism by which genetic variation between groups is kept higher than genetic variation within groups
- Kin-group selection is the special case of group selection in which individuals tend to be closely related to other members of their own group.
- the theory of kin selection does not need to assume discrete family groups
- Where they exist, tightly knit family bands, or "kin groups," may be regarded as vehicles.
- it must use phenotypic effects as intermediaries, but do these have to be bodies?
- When we look at an animal behaving, we may have to learn to say, not "How is it benefiting its inclusive fitness?" but rather "Whose inclusive fitness is it benefiting?"
- competing replicators in germ lines
- Any particular phenotypic characteristic will have to be seen as the joint product of replicators whose influence converges from many different sources, many different bodies belonging to different species, phyla, and kingdoms. This is the doctrine of the "extended phenotype."
- neither the organism nor the group is a replicator

Jan

2012

Recent Work on the Levels of Selection Problem By Samir Okasha

human-nature.com/...okasha.html

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selection evolution

the level of the biological hierarchy at which natural selection occurs. Does selection act on organisms, genes, groups, colonies, demes, species, or some combination of these?
‘multi-level selection theory’
25 more annotation(s)...
- natural selection can operate simultaneously at different levels of the biological hierarchy
- the direction of selection may be different at different hierarchical levels
- the traditional way of setting up the levels of selection question takes too much for granted
- selection will operate on any entities that exhibit ‘heritable variation in fitness’
- ideally, we would like an evolutionary theory which explains how lower-level entities became aggregated into higher-level entities,
- we need to know why lower-level selection did not disrupt the formation of the higher-level entities
- how the various levels in the hierarchy evolved initially
- ‘diachronic’ perspective
- ‘Selfish’ cells, which abandon somatic duties in favour of increased replication are selected for at the cellular level; but at the level of the whole organism, there is selection against such cells, for they disrupt organismic function
- What Dawkins fails to realise is that his argument in effect invokes group selection! From the selective point of view, genes sacrificing their independence by combining to form higher-level functional units, e.g. chromosomes or cells, is strictly analogous to individuals combining themselves into higher-level functional units, e.g. groups.
- realism versus ‘pluralism’ or ‘conventionalism’ about the levels of selection
- Aided by Hull’s replicator/interactor distinction, it was argued that to oppose genic selection to individual selection was to commit a category mistake, for genes are replicators while individual organisms are interactors, and
- entities of both sorts are involved in any selection process.
- individuals versus groups
- ‘trait-group’ models
- the trait-groups that make up the population typically exhibit differential productivity, there is selection between groups as well as selection between organisms within groups.
- One persistent source of philosophical concern in the levels of selection debate concerns the concept of causality
- causal-historical explanation
- what fraction of the total evolutionary change can be attributed to each?
- the units of inheritance rather than selection
- Dawkins, for example, used facts about inheritance, e.g. that genes are faithfully replicated across generations while whole genotypes and organismic characters are not, to privilege the gene as the unit of selection.
- Dawkins emphasised the fidelity of DNA replication as a reason for thinking of genes as the ‘ultimate beneficiaries’ of evolution, for whom all adaptations are ‘for the good of’
- advocates of ‘developmental systems theory’ (DST) such as Paul Griffiths, Russell Gray and Susan Oyama, have argued that genes are just one among many causal factors involved in development, and not uniquely responsible for the reliable transmission of biological form across generations
- Population geneticists generally define evolution as ‘change in gene frequency over time’, a definition which has considerably influenced genic selectionists such as Dawkins, but from the DST viewpoint this is a seriously distorted conception.
- Why do we speak about genetic information but not environmental information

Dec

2011

Replication (Stanford Encyclopedia of Philosophy)

plato.stanford.edu/...replication

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replication selection biology

Units and Levels of Selection (Stanford Encyclopedia of Philosophy)

plato.stanford.edu/...selection-units

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units selection population genetics gene biology

Jul

2009

Memes, selfish genes and Darwinian paranoia

Godfrey-Smith makes an excellent argument at some point in the book (chapter 7, on the gene’s eye view) that genes are not at all the sort of things Richard Dawkins and some other biologists think they are. (Psychology Today)

www.psychologytoday.com/...h-genes-and-darwinian-paranoia

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memes genes genetics evolution selection Dawkins

Jul

2009

Human Culture Subject To Natural Selection, Study Shows

The process of natural selection can act on human culture as well as on genes, a new study finds. Scientists at Stanford University have shown for the first time that cultural traits affecting survival and reproduction evolve at a different rate than other cultural attributes. Speeded or slowed rates of evolution typically indicate the action of natural selection in analyses of the human genome.

www.sciencedaily.com/...080216175953.htm

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evolution culture selection anthropology

Apr

2009

Fodor Against Darwinism

This started out to be a paper about why I am so down on evolutionary Psychology (EP), a topic I’ve addressed in print efore. (see Fodor, 19xx; 19xx). But, as I went along, it began to seem that really the paper was about what happens when you try to integrate Darwinism with an intentional theory like propositional attitude psychology.

ruccs.rutgers.edu/...Fodor_Against_Darwinism.pdf

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Fodor evolution grue selection

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