Boombustology. He applies a multi-lens approach to understanding bubbles with the aim of giving the reader the ability to identify bubbles, and thereby avoid being caught unaware.
The fifth and final lens through which bubbles are considered is the biological lens. The authors describes a couple of frameworks through which this lens can be viewed, namely using epidemic models and emergent behaviour.
Mansharamani references Robert Shiller's work in this regard. The idea is that a tellable story infects the population, eventually leading to an epidemic whereby there is a prevalent belief that results in bubble behaviour.
If the "idea" that results in bubble behaviour is considered a "disease", the epidemic model can be used to ascertain the relative maturity of the bubble. (Note that this does not allow one to time a bubble, it only gives one a rough idea of the stage at which a bubble has reached.) Epidemic models where the infection rate is greater than the removal rate follow a bell curve in terms of a population's infection (assuming the infection rate is greater than the removal, or cure, rate). Trying to ascertain where we are on that curve can help gauge bubble maturity levels.
The emergence framework has to do with how we behave in groups. Various animal groups are discussed whereby seemingly independent individual organisms appear to act as single entities when part of a group. There are a number of signals, both conscious and unconscious, that individual organisms pass on to other individual organisms that result in co-ordinated behaviour.
Humans are not immune from this type of behaviour. One example of this behaviour is an information cascade. For example, if a couple happen upon two empty restaurants and have no information about which is better, they may be indifferent as to which restaurant to choose. The next couple will have no additional information, but will see that there is one couple in one restaurant. Believing that the first couple behaved rationally in choosing their restaurant, they may choose the same one. This can occur many times, resulting in one full restaurant and one empty restaurant, even though the empty restaurant might be better. Mansharamani likens this to investors who purchase what other investors have purchased, believing that other investors must have done their homework.