A good portion of my studies have been on individual variation between and within humans. I argue that the patterns of variation in all of the various human traits are similar in nature. There are factors that create chaotic and developmental variation within humans over time. I will refer to this as “intra-individual” or “within-individual” variation. There are also factors that create infinite variation between individuals. I will call this “inter-individual” or “within-individual” variation.
I will extend my thesis it include all living organisms. I will argue that living systems use a set of universal processes that are similar across the types of living organisms and similar between various traits of interest. In my opinion, this is an important discovery since many of the traits we are interested in are “latent” or “invisible.” I will argue that we can understand the nature of traits we can’t observe by studying the nature of the traits we can observe.
The Facts of Life
I have come up with a short list of properties of living systems that seem to be unarguably “true” and should form the basis of a science of living systems. I call these properties the “facts of life.” It would seem that many scientists are ignoring one or more of the “facts of life” in their studies. For example, it is a common practice to develop theories about single causal factors. The facts of life state that there are an infinite number of causal factors causing both within individual and between individual variation. Some of the causal factors are more important, and I am not suggesting that we should not study these, but focusing on one factor ignores the rest. A more accurate model would involve some sort of multivariate regression model that takes as many of the significant factors as possible into account.
Science tends to focus on between-individual variation. I am suggesting that we need to study within-individual variation and we also need to study the interactions between factors, no matter how messy or inconvenient that practice might be. This is a relatively new scientific approach. There are a couple of interesting areas that address some of these issues. One is the science of complexity and the other involves studies of intra-individual variation. I will be covering these developments as I go on.
Fact #1: Infinite Within Individual Variation
I struggle to decide which is more important, within or between individual variation. While both are important, within-individual a.k.a. intra-individual variation seems like the better place to start. There are two main sources of within-individual variation, high dimensional chaos, and development. The level of within individual variation is often very high due to high dimensional chaos. I will argue that there is almost as much within individual variation as there is between individual variation.
Development is the second source of within individual variation and this is by far the most important. Organisms such as humans start out as a pair of one celled organisms. Humans are born, they then tend develop from helpless infants into capable adults, and finally, if they live long enough, fade into weaker versions of themselves and finally die. If one were to plot the trajectories, the range can cover any between individual measurement scheme, going from 0 to 100%.
Fact #2: Infinite Between Individual Variation
There is an infinite level of between individual variation. This can be proven through the study of genetics. Even the simplest organism has thousands of genes and millions of base pairs. As we try to find which genes cause particular traits, we often fail. The failure to find gene-disease connections is the “missing heritability problem.” Genes act through interactions between each other, with the formula for the number of possible interactions is approximately 2 to the power of N. A genetic difference of 100 genes can have 2 to the 100th power possible interactions.
The process of genetic reproduction is chaotic and inevitably produced differences between organisms. Even if two organisms start out with identical genes, the process of epigenetics introduces variation between organisms through gene-environment interactions. Even organisms that have the same genetic makeup can have epigenetic variation.
Because of the central limit theorem, variation due to many different factors creates normally distributed levels of between individual variation. Although we often can’t see the variation between individuals, any population of organisms will react differently to the same environment. For example, bacteria exposed to the same level of antiseptic have normally distributed response curves which can be plotted using the method of probits. If all organisms were identical, they would not show variation in susceptibility to antiseptic exposure.
When we start looking at rates of occurrence, the importance of the levels of between individual variation will become clearer. We need to be aware that this is a “fact of life.”