Summary of thoughts about co-evolution
I first became interested in co-evolution about three years ago. IMO of particular concern are (1) the co-evolution of obligate mutualism -- i.e., total co-dependence between two different kinds of organisms, e.g., bees and flowering plants -- and (2) the co-evolution of extremely complex parasitic relationships. In the co-evolution of obligate mutualism, unlike in evolutionary adaptation to widespread fixed physical and quasi-physical (e.g., forests) features of the environment, e.g., air, land in its different forms (e.g., forests, plains, mountains, deserts), and water in its different forms (fresh, salt, and brackish), there may be nothing to adapt to because the corresponding co-dependent trait in the other organism is likely to be locally absent. A mutant pig with wings that suddenly appears anywhere in the world can fly immediately, but bees appearing in the absence of flowers or flowers appearing in the absence of bees -- or other pollinators -- will die immediately.
The following factors are important:
(1) The co-evolution of obligate mutualism presents a particular problem because this kind of co-evolution may require simultaneous changes in both kinds of organisms in the same geographical location, because the co-dependent traits in both kinds of organisms may be immediately fatal in the absence of the corresponding co-dependent traits in the other kind of organism. In contrast, in the evolution of parasitism and commensalism, for example, change may be required -- or immediately required -- in only one of the organisms.
(2) Co-evolution is more difficult where the required change is one of kind rather than degree. For example, in buzz pollination, where the pollen is shaken loose by resonance from special vibrations of insects' wings, the pollen is contained in tubes -- it is not just a matter of the pollen adhering more strongly to the plant.
(3) Often the two co-dependent organisms can interact only in large numbers, requiring that large numbers of both kinds of organisms suddenly appear in the same place at the same time.
(4) Co-evolution is more difficult where the adaptations must be very complex and exact -- e.g., orchids' mimicry of female wasps' sex pheromones. One particular species of orchid is pollinated by only one species of wasp.
(5) Even where the co-evolution of obligate mutualism can be gradual, the gradual changes must exist in both kinds of organisms at the same time and place in order to be mutually reinforcing.
(6) Extremely complex parasitic relationships -- including multiple-host relationships -- are also a big problem for co-evolution. In some parasitic relationships, the parasite invades the nervous system of the host and produces drastic changes in the host's behavior.
(7) Co-evolution, unlike Intelligent Design, is a problem for natural selection. It has been assumed that all that is necessary for evolution to occur is to have beneficial mutations and then natural selection will assure that the best beneficial mutations will survive. However, in co-evolution, if the corresponding co-dependent trait in the other kind of organism is absent, natural selection will not occur. Also, co-evolution is a problem for "front-loaded" (pre-programmed) evolution as well as Darwinian evolution, because it may be necessary to trigger the front-loaded mutations in both co-dependent organisms at the exact same time and place.
(8) The problem of co-evolution is what I call a "non-ID" criticism of evolution -- i.e., arguments against co-evolution do not necessarily depend on any of the traits involved being irreducibly complex. However, ID can be used in arguments against co-evolution -- for example, whole sets of co-dependent traits may be irreducibly complex. For example, bees must not only be able to digest nectar, but must also be able to find the flowers. Bees are able to detect the ultraviolet light from flowers and perform a special "dance" which informs other bees where flowers are located.
Labels: Non-ID criticisms of evolution