'Prospective study' is a specific term in medical research. Note the following definitions:

Definition of Prospective study
Prospective study: A study in which the subjects are identified and then followed forward in time.
http://www.medterms.com/script/main/art.asp?articlekey=24050

A prospective cohort study is a research effort that follows over time groups of individuals who are similar in some respects (e.g., all are ...
en.wikipedia.org/wiki/Prospective_study

a study in which events or cases are observed or studied as they occur, or in which human subjects are identified and followed forward in time
www.pubmedcentral.nih.gov/articlerender.fcgi

a study that follows participants forward in time
https://workbench.axioresearch.com/NWPrecedent/glossary.htm

a study in which the investigators plan and manage the intervention of interest in selected groups of patients. As such, investigators do not know what the outcomes will be when they undertake the study. (Contrast with retrospective study.)
www.nlm.nih.gov/nichsr/hta101/ta101014.html

A prospective study asks a specific study question, usually about how a specific exposure(s) affects a specific outcome(s), recruits appropriate participants, and looks at the specific exposures and outcomes of interest in these people over the following months or years.
www.nhs.uk/news/Pages/Newsglossary.aspx

This type of “forward-looking” study is designed with a specific goal (or endpoint) in mind.
www.copaxone.com/aboutMS/glossary.aspx

Studies in which people meeting the study criteria are enrolled and then followed over a period of time in order to gain data on events or outcome ...
www.youngsurvival.org/young-women-and-bc/glossary-of-terms/

Study design where one or more groups (cohorts) of individuals who have not yet had the outcome event in question are monitored for the number of such events which occur over time.
www.fammed.ouhsc.edu/robhamm/UsersGuide/define.htm

a study that identifies factors and subjects at a certain point then studies them going forward in time.
www.breakfastresearchinstitute.org/breakfastsciencelibrary/...

An epidemiologic study in which a group of individuals (a cohort), all free of a particular disease and varying in their exposure to a possible risk factor, is followed over a specific amount of time to determine the incidence rates of the disease in the exposed and unexposed groups.
www.diabetesmonitor.com/dictionary/glossary_nhlbi.htm

In evaluations of the effects of healthcare interventions, a study in which people are identified according to current risk status or exposure, and followed forwards through time to observe outcome. Randomised controlled trials are always prospective studies. ...
www.support-collaboration.org/summaries/p.htm

A type of research study in which participants are followed over time for the effect(s) of a health care treatment.
www.spineuniverse.com/displayarticle.php/article3150.html

A study that investigats what hapens from now and onwards when giving a certain treatment. This is the best method of conducting a study of the effect of a new treatment.
www.bddiabetes.co.uk/dyn_en/glossary.html

A study that states what the objectives of the study are before acquiring patients.
www.idetprocedure.com/1000_patient/1040_glossary.html

A study that starts to watch people over time in the future. The study looks at the habits of a group of people and then follows them to see who ...
tzollarsgradproject.blogspot.com/2008/01/key-terms.html

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Note added at 7 hrs (2009-11-14 21:56:40 GMT)
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I'm not 100% sure how to work in 'social' and 'evolving'. It's possible that 'evolving' could be subsumed by 'prospective'. It definitely means evoloving as the study goes forward; it's not a reference to evolution in the Darwinian sense.