Of the many lenses of psychology: evolutionary psychology

It is fascinating how remember that humans are animals could teach us a few things about human behavior.

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Called by some authorities as a lens rather than a branch, evolutionary psychology aply the theorical framework derived from darwinian model of evolution. By analysing conducts through the paradigm of evolutionary biology (darwinian evolution), the psychologist seek examine the rationality of the the purpose and mechanics of these conducts in term of fitness and selection, to then apport a innately o biologically informed explanation to the observancy of these conducts. Fitness is therefore understood as "how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it"(1), constituying a measure of success under selection. In other words, by studiying how a behavior or trait would grants any benefit (or cost)  to the person on a natural setting, it can be rationalized the presence of such behavior or trait in human history. 

Of course, you would be asking, how were theses behavior governed then and in which setting they where selected or deemed beneficial? 

Because evolution traditionally appeal to stable, biologically based factors, necessarilly genetics and neurology must enter in the conversation; this mean that  unconscious, instictual or innate mechanics would be discussed as the proximate process to explain the manifestation of the behavior. 

Evolutionary psychologists often rely in the Massive Modular Hypothesis and the Savannah Principle to explain the purpose of a behavior around a tast-related and contextual needs. According to theses hypothesis, the mind is subdued by neural structures or modules developed or designed by selective forces (MM Hypothesis) to navigate the life in the paleolithic, being this the establised evolutionarily function (Savannah Principle). Both hypothesis tend to be supported by the psychologist of the Santa Barbara School, being the major proponents the co-founders of the center the anthropologist and psychologist  John Tooby and Leda Cosmides, respectively. 

In sum, evolutionary psychologists try to explain a behavior through a cost-benefist approach —almost an economicist one, in which any trait that maximize the possibilities of surviving or reproduce in a natural setting are deemed beneficial and thus selected over generation, hence the conservation until our days. In that way, we are speaking about adaptation and functionality.

However, there are important criticism with respect to this inter-discplinary approach. The field of philosophy of biology has argued that the appeal to pattern, design adaptationism fall into over-atribution and without futher clarifications, that suffers of untanable reductionism, the lacking of evidence about modules and that the theoric baggage is mostly speculative at best  (Griffiths 1996 an 1999; Richardson 1996; Lloyd 1999; Richardson 2007;  Dupre 1999; Dupre 2001). It could be counter-argued that adaptationism is not always concieved as an aim, but it can be a by-product or vestige; at the same time, is important distinguish between adaptative and adaptation, and ontogenic adaptation and philogenetic adaptation, hence they not always rely in apparent designs(2). On the speculative side, evolutionarily or biologically informed behavioral science are relativily new, which mean that the field need still walk a long road in terms of improvement of the methods; because the importance of determine patterns, a comparative method in modern days is often use instead of trying to record the way of life and the setting of past time. That is why the Savannah Principle is not an asumption that must constrains the field.

(1)  " What about fitness?" Understanding Evolution. University of California Museum of Paleontology. 04 August 2018: http://evolution.berkeley.edu/evolibrary/article/evo_27  

(2)  Downes, Stephen M., "Evolutionary Psychology", The Stanford Encyclopedia of Philosophy (Winter 2017 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/win2017/entries/evolutionary-psychology