Month: September 2022

FOUR MODELS. "Several models have been advanced to account for a naturalistic origin of the complexity seen in biological systems. Following are brief descriptions of four models advanced to account for the origin of biological complexity." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #1. "The incremental additions model hypothesizes that an initial association of components favorable to some function may become an essential association through time. The complexity of the system may increase with the addition of new components." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #1 NARRATIVE. "Suppose, for example, that a molecule carries out a particular catalytic function. If an association with another molecule enhances that function — for example, through structural stabilization — then natural selection can favor the association. The second molecule is initially beneficial although not essential. The second molecule may become essential, however, if an inactivating mutation in the first molecule is compensated for by the presence of the second." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #1 NARRATIVE. "There are numerous examples of molecules whose function is enhanced in the presence of another molecule. Consider the activity of RNase P (an RNA-protein complex responsible for processing transfer RNA molecules). The RNA component of the molecule possesses the catalytic activity and has been shown to function without its protein partner, albeit at a very much lower activity." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #2. "Scaffolding is another mechanism whereby irreducible complexity might be established. In the incremental additions model, a beneficial association of components becomes an essential association because mutational events compromise the independent activity of one or more component parts. In the scaffolding model, superfluous components are lost, leaving a system in which the remaining components appear tightly matched as if they were specifically designed to fit and function together." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #2 NARRATIVE. "Many biochemical systems are characterized by “redundant complexity”. Biochemical pathways rarely function in isolation; rather, one pathway interconnects with another." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #2 NARRATIVE. "Metabolic systems can be viewed as complex traits, because individual metabolic enzymes in isolation are rarely pertinent to in vivo physiology until they become part of an organized metabolic pathway. Extant metabolic pathways in general contain a set of enzymes catalyzing sequential reactions in a highly concerted manner." http://onlinelibrary.wiley.com/doi/10.1111/nph.12416/full View in LinkedIn

MODEL #2 NARRATIVE. "Carbon atoms entering the Calvin-Benson cycle within a chloroplast may find their way into any one of many different molecules and be shunted into other pathways. There are also many cases of a redundancy of enzymatic components, or variant isoforms. Gene duplications increase the number of genes in a species, which can then evolve in different ways." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #3. Co-option model. "Natural selection acts upon an existing set of structures within a particular environmental context. An altered environment demands altered responses from an organism. Consequently, it should not be surprising to find in the fossil record and in comparative anatomical and physiological studies evidence that some structures have been modified through time to serve different functions." https://lnkd.in/dJG4bYH View in LinkedIn

MODEL #3 CO-OPTION. "In fact, a common theme of biological evolution is that existing structures are often put to new uses, and new structures are created from the old. “Co-option” is the term used to describe the recruitment of existing structures for new tasks. This recruitment can explain evolutionary increases in biological complexity." https://lnkd.in/dJG4bYH View in LinkedIn