Great article. Humbly I would suggest that perhaps inflammatory responses that effect the brain and cause depression aren’t an evolutionary advantage but rather the combination of at least two problems occurring simultaneously, seen more in a modern world than an ancient one due to our diets and lifestyles. The first is the inflammatory cascade, which may just be a natural reaction to something like you say, but the second and the more serious could be that the BBB has been degraded and is no longer effectively doing its job. I could speculate as to why this may happen; the BBB may be degraded due to a chronic inflammatory state effecting many mucous membranes including the gut lining. For example, diabetes or obesity will increase circulating levels of LPS which can disrupt the BBB and reduce its effectiveness. Add an infection like the one you suffered with for a night or an allergic reaction and hey presto, depression. From personal experience I can tell you that a food allergy will have the precise same effect on me, some horrible ‘treat’ like a donut, all oxidised vegetable oils, sugar and highly processed wheat will leave me unable to function for a day due to mental anguish. It hits me within 30 mins too, which is how I spotted it after about the third episode thankfully.