Selection Unit in Evolution

[dttom]

As CharonY has suggested, some of my points about the evolutionary selection unit in my previous thread titled 'About mutualism between human and E.coli' would be described here and for open discussion.

 

The main idea is that I believe the selection unit is not fixed over the evolutionary time, instead, the level of this unit could change depending on circumstances. One of the important factor should be period of time available for resolution of a gene from its corresponding bundle (gene assembly). The statements about this point was quoted from my previous thread as below:

 

 

"I should agree that for each time of selection (who dies, who lives), natural selection acts on individual level, so at genomic level; however, in long run, why shouldn't it act on genes' level, fostered by crossing over in meiosis? A complication arrives with speciation that, as genes in a genome are bundled together, if a gene could not be resolved (if a gene is resolved, it got the chances to be in different genomes (of course in different individuals) for natural selection) before microevolution occurs, probably the selection level could stay at a higher level than a gene.

 

When talking about a gene could only exert its effect in a given genetic environment (together with other genes), as in the case of any individual, I have to admit that this is definitely the fact. But does this fact affect or change the consideration in selective level is another matter. For me this is a fact stating that a gene could have different effects in different combinations of genes (actually I would prefer, and better to, use the word gene assembly), but as long as a gene could be resolved, it got the chances to be in different genomes, and individual gene effect could be selected by natural selection. The result could be a gene might exert more advantageous effect when combining with a set of other genes (actually this is usually the case as a phenotype, no matter is the traditional definition of phenotype or the extended phenotype, is usually determined not by a single gene), in this case, such a gene assembly would be advantageous if they have a low COV relative to each other (harder to resolved from each other), ultimate result might be fusion to a single gene (please beware of the use of the word 'gene', not cistron, a 'gene' here could refer to a number of encoded polypeptides) which is selected later as single unit (this might be refered to by someone as an evidence to support the allegation of selection at a level higher than gene, so for me it is not a matter of concept but a matter of definition, view of phenomenon and explanation)."

[CharonY]

Well evolutionary models can be derived on the gene level, which is done routinely. However, if you want to make population studies and derive for instance the chance of fixation, you will have to figure in fitness. The latter can only be achieved by measuring on the level of reproductive units, which generally means the whole organism. Even mobile genetic elements, which are as individual as possible when it comes to genes need a vehicle to persist through generations. Though of course the horizontal transfer can be measured with other metrics.

[Mr Skeptic]

Another example would be social behavior. Suppose you had two societies with behavior that was not determined by their genes. For example, one society takes up hunting and the other farming, and the knowledge and behaviors necessary for this are taught via social interactions, not genetically inherited, and are long lasting traditions. Would not the societies as a whole be subject to selection? People can form new societies and move from one society to the other, and the new societies might "inherit" attributes of former societies. If a society runs out of people it is dead.

 

Of course, individuals within the society would also be selected for, and societies haven't really lasted all that long compared to genes, but wouldn't it still be possible to have societies as units of selection? Selecting for non-genetic social behaviors?

[npts2020]

Another example would be social behavior. Suppose you had two societies with behavior that was not determined by their genes. For example, one society takes up hunting and the other farming, and the knowledge and behaviors necessary for this are taught via social interactions, not genetically inherited, and are long lasting traditions. Would not the societies as a whole be subject to selection? People can form new societies and move from one society to the other, and the new societies might "inherit" attributes of former societies. If a society runs out of people it is dead.

 

Of course, individuals within the society would also be selected for, and societies haven't really lasted all that long compared to genes, but wouldn't it still be possible to have societies as units of selection? Selecting for non-genetic social behaviors?

 

Isn't that what memes are all about?

[dttom]

Well evolutionary models can be derived on the gene level, which is done routinely. However, if you want to make population studies and derive for instance the chance of fixation, you will have to figure in fitness. The latter can only be achieved by measuring on the level of reproductive units, which generally means the whole organism. Even mobile genetic elements, which are as individual as possible when it comes to genes need a vehicle to persist through generations. Though of course the horizontal transfer can be measured with other metrics.

 

I think the reason why evolutionary models could be derived on the gene level is basing on the assumption that there were enough time for genes to resolve so as to be considered as a single unit for selection (otherwise I think they would be selected in a unit of gene assembly). And not only the case of population study I think in all case the unit for each turn of selection should on the level of individual, or genome. Provided with long enough period of time, the phenotypic unit of selection will shift from genome to gene assembly, then to gene itself.

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Isn't that what memes are all about?

 

Yes I think the idea described by Mr Skeptic is about meme. And I do think this has exerted a prominant effect on haminity and culture evolution.

[Mr Skeptic]

Well memes described natural selection acting on individual ideas. What I described is related but slightly different. I guess my description would be a memeone? (as gene is to genome, meme would be to memeone)

[dttom]

Well memes described natural selection acting on individual ideas. What I described is related but slightly different. I guess my description would be a memeone? (as gene is to genome, meme would be to memeone)

 

If it is 'memeone', then I suspect the case would be a bit different. In traditional gene selection, natural selection force acts on individual by 'death or live', hence for each turn of selection the unit would be genomic. But in the case of meme, each turn of selection should actually be within single society before two societies could be selected against. If a society containing a set of meme that is inferior to another set of meme within another society, assuming there is no meme flow, there should come first meme selection then memeone selection (society selection), in other words, the vanish of one society should follow a series of meme selections. So in this case I believe memeonic selection is a result of long-term meme selection provided with long enough period of time for serial meme selections to effect in a system with certain degree of meme isolation.

 

However, the case becomes very different if taking meme flow into consideration. As each turn of selection acts on meme scale, one can use a model that favorable meme would have higher propagation rate, as this meme propagation could flow freely between societies, or meme pools. Here provides no chance for memeonic selection, just as if there would not be speciation if no isolation force exists (speciation similar to divergence in meme pools, or societies). This model bases on totally free meme flow, which exists only theoretically, yet in reality the situation is coming closer and closer to this limit with the advance in information electronics (we are now using this forum to share ideas...).