A puzzle in evolutionary theory: how can single mutations be responsible for the kinds of morphological differences among species? To add an extra toe, for example, requires many (10s or 100s) of different genes to be expressed at different times during development. To go from gills to lungs requires even more changes in gene expression and a few new genes. Mutating these genes sequentially, one at a time, is highly disadvantageous, since the original function will be disrupted. This is akin to going from a carburated car to a carburated car with a fuel injector between the carburetor and the intake manifold in the evolution of cars--the mutant won't run. In fact there is no path of single component changes in a car going between carburation and fuel injection, which won't kill the car. These changes have to be done all at once, in a single generation, to produce a viable car.
What if the new fuel injector is not connected between the carburetor and the intake manifold? There is some energy expended in building it, which presents a slight disadvantage to the manufacturer of the car. But if the manufacturer has some resources to do R&D, eventually a fuel injection system can be evolved. Of course the analogy breaks down here as there is no manufacturer in biology. But I think that the part about large changes occuring without a phenotype might happen in nature too, as in lungs being built without being used. Also, the analogy with the manufacturer is a regulatory gene, which controls the expression of many other genes. In technology, the manufacturer is not part of the car, but in biology the regulatory gene is part of the organism.
Several things have to happen in order to produce the multitude of beneficial changes leading to a new species, even after reproductive isolation. First, mutations occur in one or a few regulatory genes, as opposed to hundreds of genes. This enables many genes to change their expression with the mutation of only one or a few of the genes that regulate them, making the probability of change within a (consistent with paleontological record) short time reasonable.
Second, at least one copy of the unmutated regulatory gene has to continue to express normally and be dominant, in order that normal function not be disrupted. Since most genes are recessive, this requires gene duplication, an occasional occurence, followed by mutation in one of the copies, followed by homozygosity of the mutated gene.
Third, either the environment has to change or new phenotypically invisible mutations (either in the originally mutated gene or in cooperating genes) have to occur in order to provide a differential selective advantage for the new gene relative to the original gene. It is possible that the original mutation is good enough to provide an advantage (once the environment changes) relative to the original unmutated gene, with no new mutations, but to me this seems unlikely, even for a mutation in a regulatory gene. Such an event would seem to lead to a new variety or strain rather than a new species. Species are separated by barriers in multidimensional fitness space and most changes, even multi-gene ones, are unlikely to lead to a lower valley on the first try.
Fourth, a new mutation occurs such that the original gene is inactivated, or the new gene becomes dominant.
The fourth event happens many times, most of which are not preceded by the third step, in which case no new species arises. The changes involved in speciation are numerous and interdependent and must remain invisible to selctive pressure until the time is right.
Now I would like to argue that similar considerations apply to cultural evolution, as do to biological and technological evolution. Culture is a hereditable system composed of interacting memes, subject to selective pressure and variation. Gradual, non-regulatory mutations lead to different strains. Reproductive isolation is a necessary (see the entry on gradual vs quick speciation) but not sufficient condition for new species to arise. The four steps above might complete the ingredients necessary for cultural speciation to occur, although I may have missed some. In the pictures below I draw a simplified draft of an outline of the mainstream culture and a culture I would like to speciate into. I try to represent some regulatory memes in the center. These mutations have already occured but they are either conferring a disadvantage or phenotypically invisible. We need a community to work them out, largely isolated from mainstream culture, in an environment where the new culture would have an advantage.
What if the new fuel injector is not connected between the carburetor and the intake manifold? There is some energy expended in building it, which presents a slight disadvantage to the manufacturer of the car. But if the manufacturer has some resources to do R&D, eventually a fuel injection system can be evolved. Of course the analogy breaks down here as there is no manufacturer in biology. But I think that the part about large changes occuring without a phenotype might happen in nature too, as in lungs being built without being used. Also, the analogy with the manufacturer is a regulatory gene, which controls the expression of many other genes. In technology, the manufacturer is not part of the car, but in biology the regulatory gene is part of the organism.
Several things have to happen in order to produce the multitude of beneficial changes leading to a new species, even after reproductive isolation. First, mutations occur in one or a few regulatory genes, as opposed to hundreds of genes. This enables many genes to change their expression with the mutation of only one or a few of the genes that regulate them, making the probability of change within a (consistent with paleontological record) short time reasonable.
Second, at least one copy of the unmutated regulatory gene has to continue to express normally and be dominant, in order that normal function not be disrupted. Since most genes are recessive, this requires gene duplication, an occasional occurence, followed by mutation in one of the copies, followed by homozygosity of the mutated gene.
Third, either the environment has to change or new phenotypically invisible mutations (either in the originally mutated gene or in cooperating genes) have to occur in order to provide a differential selective advantage for the new gene relative to the original gene. It is possible that the original mutation is good enough to provide an advantage (once the environment changes) relative to the original unmutated gene, with no new mutations, but to me this seems unlikely, even for a mutation in a regulatory gene. Such an event would seem to lead to a new variety or strain rather than a new species. Species are separated by barriers in multidimensional fitness space and most changes, even multi-gene ones, are unlikely to lead to a lower valley on the first try.
Fourth, a new mutation occurs such that the original gene is inactivated, or the new gene becomes dominant.
The fourth event happens many times, most of which are not preceded by the third step, in which case no new species arises. The changes involved in speciation are numerous and interdependent and must remain invisible to selctive pressure until the time is right.
Now I would like to argue that similar considerations apply to cultural evolution, as do to biological and technological evolution. Culture is a hereditable system composed of interacting memes, subject to selective pressure and variation. Gradual, non-regulatory mutations lead to different strains. Reproductive isolation is a necessary (see the entry on gradual vs quick speciation) but not sufficient condition for new species to arise. The four steps above might complete the ingredients necessary for cultural speciation to occur, although I may have missed some. In the pictures below I draw a simplified draft of an outline of the mainstream culture and a culture I would like to speciate into. I try to represent some regulatory memes in the center. These mutations have already occured but they are either conferring a disadvantage or phenotypically invisible. We need a community to work them out, largely isolated from mainstream culture, in an environment where the new culture would have an advantage.
A corollary to the above considerations is that small changes are not going to radically change the culture, even given an infinite amount of time. Herbert Marcuse already saw this many years ago with regards to capitalism, but it is a property of all stable evolutionary systems. In the next entry I will elaborate on why the following changes will not create a new culture.
mono->poly without changing capitalism
greener consumption habits without changing capitalism and empire
changing capitalism without localization
localization of food without participation in agriculture
localization of food without localization of industry
green building without changing attitudes about housing
shared housing without a common vision and common livelihhod
no electricity without common recreation
folk dancing without an attitude of group communion
communalism without consensus
No comments:
Post a Comment