Theoretical biologist Paul Weiss started his introductory biology courses by presenting two test tubes to the class. One test tube contained viable embryos and the other contained embryos after homogenization (basically blending them). He asked the class why, despite having the exact same chemical constituents, the viable embryos would be considered living, while the other test tube wasn’t. This exercise was meant to highlight the absurdity of reducing organisms to just their chemical constituents, and that interactive and combinatorial processes were more important to understanding organisms than simply knowing what they were “made of”. Today, esteemed biologists such as Jerry Coyne seem to be moving in the opposite direction, suggesting that organisms and behavior can be understood as outcomes of the chemical compositions of our cells and genes. Bioinformatics approaches to biology such as Genome-Wide Association Studies and RNAseq seek to link phenotypic traits with the presence or amount of molecular “components” in specific tissues.
Such a strong reductionist perspective cannot provide a complete picture of organisms. Most of us have spent time as children playing with Lego blocks. Like many biological processes, the interactions between molecules scale up to build larger structures, just as Lego blocks can be combined to make houses, boats, animals or other structures. The shape of Lego blocks prevents the formation of specific structures, as it's impossible to make a perfect sphere with rectangular blocks. You could even compute all the potential structures that can be built with a series of blocks, by modeling all the ways those blocks could connect to each other. Nonetheless, even with this knowledge we still have a very limited understanding of what actually will get built in real life situations. A complete catalog of all the Legos in a toy basket won't allow you to predict what structure a child will build. In order to understand the final structure, you need to understand the processes where the blocks are placed together. Thus, having a catalog of blocks allows you to calculate all the potential structures that could be built, but it can't predict which structures actually are built (the set of components defines the boundaries but not the specific outcomes).
Many biologists, neuroscientists, and psychologists don't just seek to catalog the material components that make up organisms but to uncover mechanisms that capture how those components interact to influence the functional properties of organisms. Unlike Legos, the molecules in living systems are reactive. Entire research careers are often centered on a series of specific genes or molecules and how they react with other molecules to form physiological pathways that have functional outcomes. For instance, the gene VLDLR plays a critical role in the reelin pathway that is involved in cell-to-cell cohesion, neural migration, and diseases such as atherosclerosis. The assumption of such research programs is that a full catalog of all the mechanisms associated with some functional property, such as hunger, will lead to a complete understanding of that property. Such an assumption is called micro-determinacy where the interaction between the parts scales up to functional organism-level outcomes. Here causality is a one-way street from molecules to the organism.
While mechanistic studies have been essential to uncovering key molecular pathways involved in nearly all aspects of living systems—from hormonal regulation of behavior to the neurogeneitc influences on learning, to trans-generational epigenetic inheritance, and development of novel medicines – the assumption that a complete catalog of mechanisms will allow for a complete understanding of living systems is coming under increased criticism. Recently, there have been attempts to test the effectiveness of such mechanistic approaches by applying standard methodologies from the biological and neurological sciences to human-engineered objects, such as a microprocessor running a video game or a radio. These studies test how effective our methods are at uncovering a “complete” understanding of the system under investigation. For instance, a common technique in behavioral neuroscience and genetics is to “knockout” specific brain regions or genes and observe their influence on the phenotype. Similarly, you can do a “knockout” experiment on electronic devices by removing components and observing changes in how the device functions. The results from such studies are sobering. In none of the studies were the approaches ever able to reverse engineer the system.
Such findings highlight some real limitations of reductionist attempts to understand complex systems. Such criticisms do not take away from the obvious and widespread advances that such reductionist endeavors have achieved, but rather highlight how new concepts and methodologies might help to integrate experimental findings across levels into a less fragmented, more holistic, understanding of living systems. So where do we go from here? I propose that we start viewing organisms not as a static object but as a lifecycle. A lifecycle is a developmental system that is initiated at conception and flows until death.
Organisms have little in common with Lego structures, radios, or computers. A defining feature of organisms is that they are thermodynamically unstable open systems that build and maintain themselves over time through a continual exchange of materials with the environment (also known as autopoiesis). From the moment of birth (or hatching, ect..) organisms are fighting for their lives. As highly organized systems, organisms must constantly engage with their environments to maintain their integrity. They must eat, drink, and breathe, in order to get the raw environmental materials to build and maintain themselves. Such materials are almost never uniformly distributed in the environment and usually occur in patches or gradients. This means that organisms must be active, by moving and interacting with their environment in order to secure and utilize the resources needed to persist over time. A plant grown in a dark room must take advantage of light gradients and grow toward high light levels to survive. The newborn rat must recognize and move toward their mother's nipple to secure milk. Even seemingly sessile organisms, such as barnacles must be active, by extending their filter like cirri into open water during periods when food is available.
In general, there are two ways that all organisms can interact with their environments: they can either approach specific environmental stimulation, or they can withdraw from it. The comparative psychologist T. C. Schneirla was the first scientist to recognize this “biphasic process of approach-withdrawal” in his now classic 1959 paper, “An evolutionary and developmental theory of biphasic processes underlying approach and withdrawal.” Here, he outlined the basis of his comparative psychology, that developmental processes largely result from a refinement of approach/withdrawal behaviors that seek to perpetuate an organism's lifecycle, allowing them to grow, sustain themselves and reproduce (create new lifecycles). Organisms should approach and utilize resources in the environment that progresses their lifecycle, and avoid aspects of the environment that will work against the continuation of their own, or their offsprings lifecycle.
[[ to be continued in part 2 ]]
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