Clinical Depression in the Context of Human Evolution

If evo­lu­tion ensures sur­vival of the most adapt­able species, how did it not van­quish men­tal depres­sion in humans? This ques­tion has been on my mind for sev­er­al years, and it is time to exam­ine it in the con­text of a new hypoth­e­sis pro­posed by two sci­en­tists.

Background

Between 30 to 50% peo­ple suf­fer from a major depres­sive episode in their life­time. It is gen­er­al­ly con­sid­ered to be a dis­ease of the brain, an ill­ness that needs treat­ment. In the mil­lions of years of human evo­lu­tion, nat­ur­al selec­tion was at work, ensur­ing that the ones among us who were best at sur­viv­ing, adapt­ing, and repro­duc­ing, car­ried the human species for­ward. Men­tal depres­sion reduces ones abil­i­ty to sur­vive, adapt, and repro­duce. It would then be rea­son­able to expect that those humans afflict­ed with this dis­ease would have become extinct by now. The genes respon­si­ble for, or con­ducive to depres­sion, should have erod­ed out of the thriv­ing gene pool. But that, as we know, is far from the truth.

While ani­mals are also known to expe­ri­ence depres­sion, it is still an emerg­ing field of research, and I am skep­tic whether their sad­ness is just a ratio­nal response to exter­nal cir­cum­stances or is full-blown cause­less depres­sion like in humans.

Mered­ith Small, an anthro­pol­o­gist at Cor­nell wrote last year:

The capac­i­ty to feel pre­sum­ably helps us solve prob­lems and sur­vive, and is essen­tial for group liv­ing, and per­haps incon­solable depres­sion is sim­ply emo­tion­al bag­gage that tags along with the good stuff. Or maybe unhap­pi­ness and a ten­den­cy towards sui­cide is the prod­uct of the uncon­trolled nature of our quick­sil­ver minds. We think a lot, and our won­der­ing minds are just as like­ly to think sad as hap­py.

Live­Science quotes Mered­ith in Why Did Evo­lu­tion Pro­duce Depres­sion, along with Paul Andrews and J. Ander­son Thom­son, Jr., who have argued in Sci­en­tif­ic Amer­i­can that “depres­sion is in fact an adap­ta­tion, a state of mind which brings real costs, but also brings real ben­e­fits.”

The Hypotheses

The two sci­en­tists have pub­lished their views in a Sci­en­tif­ic Amer­i­can arti­cle “Depression’s Evo­lu­tion­ary Roots”. The key points:

  1. Depres­sion should not be thought of as a dis­or­der at all. They argue that depres­sion is in fact an adap­ta­tion, a state of mind which brings real costs, but also brings real ben­e­fits.
  2. One rea­son to sus­pect that depres­sion is an adap­ta­tion, not a mal­func­tion, comes from research into a mol­e­cule in the brain known as the 5HT1A receptor….The abil­i­ty to “turn on” depres­sion would seem to be impor­tant, not an acci­dent.
  3. Depressed peo­ple often think intense­ly about their prob­lems. These thoughts are ana­lyt­i­cal and per­sis­tent. Depressed peo­ple have dif­fi­cul­ty think­ing about any­thing else. This ana­lyt­i­cal style of thought, of course, can be very pro­duc­tive and can help you solve the prob­lem caus­ing the depres­sion.
  4. Analy­sis requires a lot of unin­ter­rupt­ed thought, and depres­sion coor­di­nates many changes in the body to help peo­ple ana­lyze their prob­lems with­out get­ting dis­tract­ed.
  5. Symp­toms of depres­sion make sense in light of the idea that analy­sis must be unin­ter­rupt­ed. The desire for social iso­la­tion helps the depressed per­son avoid sit­u­a­tions that would require think­ing about oth­er things. Inabil­i­ty to derive plea­sure from sex or oth­er activ­i­ties pre­vents the depressed per­son from engag­ing in activ­i­ties that could dis­tract him or her from the prob­lem. Even the loss of appetite could be viewed as pro­mot­ing analy­sis because chew­ing and oth­er oral activ­i­ty inter­feres with the brain’s abil­i­ty to process infor­ma­tion.
  6. If depres­sive rumi­na­tion were harm­ful, then bouts of depres­sion should be slow­er to resolve when peo­ple are giv­en inter­ven­tions that encour­age rumi­na­tion, such as hav­ing them write about their strongest thoughts and feel­ings. How­ev­er, the oppo­site appears to be true. Sev­er­al stud­ies have found that expres­sive writ­ing pro­motes quick­er res­o­lu­tion of depres­sion, and they sug­gest that this is because depressed peo­ple gain insight into their prob­lems.
  7. There is anoth­er sug­ges­tive line of evi­dence. Var­i­ous stud­ies have found that peo­ple in depressed mood states are bet­ter at solv­ing social dilem­mas.
  8. Depres­sion is nature’s way of telling you that you’ve got com­plex social prob­lems that the mind is intent on solv­ing. Ther­a­pies should try to encour­age depres­sive rumi­na­tion rather than try to stop it, and they should focus on try­ing to help peo­ple solve the prob­lems that trig­ger their bouts of depres­sion.

Critique of An Unquiet Mind

  1. The seman­tic dif­fer­ence between “dis­or­der” and “adap­ta­tion” has huge ram­i­fi­ca­tions and con­se­quences in how soci­ety treats depressed peo­ple. These gen­tle­men have per­haps not thought through these ram­i­fi­ca­tions. By their own account, they describe the unhealthy, self-destruc­tive, treat­ment-wor­thy behav­ior of peo­ple in this state of mind, so what goals do we achieve by terming them an adap­ta­tion rather than an ill­ness, dis­ease, or dis­or­der?
  2. I am not sure if this is “miss­ing the wood for the trees”. Human­i­ty would ben­e­fit great­ly if sci­en­tists study­ing the brain and depres­sion focus on their excel­lence at deal­ing with trees and not try to paint the woods.
  3. Ana­lyt­i­cal and per­sis­tent think­ing in depres­sion is usu­al­ly in the form of obses­sion and brood­ing – two words, often asso­ci­at­ed with depres­sion, con­spic­u­ous­ly miss­ing in the arti­cle. The obses­sive nature of think­ing in depres­sion is rarely pro­duc­tive, and often self-destruc­tive.
  4. Deal­ing with lack of dis­trac­tion in the next point, here I would like to point out the con­spic­u­ous absence of the dis­cus­sion of anx­i­ety in the arti­cle. Most forms of depres­sion are close­ly asso­ci­at­ed with anx­i­ety, and there is no dis­cus­sion of whether anx­i­ety also con­tributes to “pro­duc­tive ana­lyt­i­cal think­ing”.
  5. Unin­ter­rupt­ed “analy­sis” often leads to sui­cide. Not eat­ing leads to seri­ous phys­i­cal harm. Sub­stance abuse is also a seri­ous prob­lem with those afflict­ed with the ill­ness of depres­sion. The idea that sui­cide, star­va­tion, and sub­stance abuse “can be viewed as pro­mot­ing analy­sis” is not just ridicu­lous, but very insen­si­tive. The brains abil­i­ty to process infor­ma­tion is not enhanced by any of these activ­i­ties.
  6. The stud­ies con­firm that emo­tion­al expres­sion is an impor­tant heal­ing fac­tor in depres­sion. It is not just the writ­ing, but the fam­i­ly, friends, con­sul­ta­tion and ther­a­py that fol­lows it, which is often cru­cial for resolv­ing issues.
  7. The first study is of whether mood influ­ences lev­el of coop­er­a­tion in peo­ple and had just two exper­i­ments. The sec­ond exam­ines how fam­i­ly rela­tion­ships are rel­e­vant to ado­les­cent depres­sion. The notion that peo­ple with depres­sion are bet­ter at solv­ing social dilem­mas is again, pre­pos­ter­ous and high­ly insen­si­tive.
  8. Many forms of human depres­sion have no cause in the exter­nal world. It is not a ratio­nal response to an exter­nal social prob­lem. It is often cause­less and intrin­sic or inborn. The sci­en­tists view of depres­sion seems to be very nar­row mind­ed.

Conclusion

It is clear that we do not have any def­i­nite answer yet. Though Depres­sion has been stud­ied in all cul­tures, we do not know if it exist­ed in ear­ly stages of evo­lu­tion. If it didn’t, and we find that it has devel­oped in recent his­to­ry (in evo­lu­tion­ary terms), I’m sure nat­ur­al selec­tion will even­tu­al­ly elim­i­nate it.

Mean­while, it does not behoove Sci­en­tif­ic Amer­i­can to pub­lish such arti­cles. If you want to learn about men­tal depres­sion, here is the best place to start.

SaltedLithium

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  • I had also read about this the­o­ry and had in fact book­marked that arti­cle as I found it very inter­est­ing. The sub­ject of evo­lu­tion and genet­ics fas­ci­nates me. But ofcourse we do not have all the answers as yet although research in this field seems to be grow­ing by leaps and bounds.
    I think this new the­o­ry does have some basis. After all a lot of peo­ple who are genius­es are also a lit­tle men­tal­ly dis­turbed. I can think of many poets and writ­ers who did in fact com­mit sui­cide. I don’t the com­plete answer, but as you men­tioned, a lot more work needs to be done in this area.

  • Hi Nita, thanks for the com­ment. Yes, it is a fas­ci­nat­ing sub­ject, and I was dis­ap­point­ed with this par­tic­u­lar hypoth­e­sis.

    There is some basis for adap­tive the­o­ries of depres­sion, but I need to inves­ti­gate and study them fur­ther. With this post, I want­ed to “break in” on this top­ic. 🙂

  • Thank you for your humane analy­sis of the so-called ben­e­fits of depres­sion. When some­one is suf­fer­ing our job as fel­low human beings is to help them.
    Richard Zwolin­s­ki
    LMHC, CASAC