Is paper refering on pop science books less value? I have a paper in linguistic which was written when I was in high school. I would like to mention it in my SOP. When I ask if I should mention it, xLeitix has raise this question:


  What is the hypothesis that you proposed?


The hypothesis I proposed is in sociology, which I had when reading the book The Human Zoo. The problem is, it is a pop science book, and the hypothesis only bases on this reference (number of total references is 7). However, since the author is reputable (he is listed as a notable English-language popularizers of science by Wiki), I think I have cited a reliable source. More importantly, if the PhD committees are interested in the ability of research, does this paper satiate them because I made it when I was in high school without any guidance? Does citing on pop science books make my paper less value in the eyes of:


linguists?
biologists?
other scientists?
The main problem with citing a popular science book is that it is a secondary source.  Almost certainly, the author isn't reporting on original research that he conducted himself; he's discussing research previously discussed and published by others (and possibly his own as well), and putting it in context for a general audience.  He is one or more steps removed from the original work itself, and especially in a popular science book, there won't be complete details about how the results were obtained, which would be necessary to satisfy an expert.

So if you want to support your own arguments using some statement claimed in Morris's book (e.g. "baboons can use toothbrushes"), you don't want to cite this book as your only evidence for that statement.  Rather, you need to find the primary sources.  You should look for who Morris cites, and if necessary, trace back a chain of citations until you find the original paper where this result was reported.  This will be a paper written by the people who actually conducted the study that is claimed to show that baboons can use toothbrushes (call them Jones).  Read Jones's paper, and make your own decision about exactly what hypothesis they tested, whether their methods were appropriate, whether their data is good evidence for their hypothesis, and in general whether their work convinces you that baboons can use toothbrushes.  Then search for other papers citing Jones that may offer criticism of their work, reproduce their results, and so on.  Take them into account in your decision as to whether to depend on this fact.  If you decide it's reliable, then cite Jones and any other paper that offers something helpful to evaluating their work.  

(And if you decide it's not reliable, don't fall into the trap of "But Morris believes it, and he's reputable, so I'll just cite him."  Reputable people make mistakes too, and propagating mistakes like this is a major cause of bad science.  Instead, look for other evidence to support or refute your argument.)

You can also cite Morris, if you feel that he adds something to the discussion, or that the reader will find it useful to read his book.  But a scholarly paper can't rely solely on secondary sources.  A paper that does so will certainly be taken less seriously, by anyone.

Edit: To address your comment, nobody here can really tell to what extent a PhD committee would view your paper as evidence of research ability; it will depend on how good they think it is, and only they know that.  But citing popular science texts instead of primary sources is probably not a good sign, since it doesn't seem to show a familiarity with proper research practices.  I wouldn't really expect a committee to be extra impressed because it was done in high school.  They don't really care how advanced you were in high school, they want to know whether you are prepared for grad school now, and that decision will be based much more on what you have done in your undergraduate work.  So unless the paper you wrote in high school was incredibly spectacular, I don't think it will affect graduate admissions one way or the other.