Several recent conversations concerning genealogy have ended rather suddenly, on my part, when the person claimed to have his or her genealogy "back to Adam." I really don't have any polite way to respond to that conclusion. I have written before about the physical impossibility of obtaining such a lengthy pedigree, but recent conversations have caused me to return to the subject. The real question is where does genealogical research end as a practical and reasonable endeavor?
Part of the complication of a discussion in this area, is the issue of the infamous genealogical "brick wall." Anytime further research is characterized as a brick wall, there is an unspoken assumption that some kind of further research involving hitherto unavailable records, will continue to extend the pedigree. The literature is replete with anecdotal examples of researchers finding the long lost relative. I have no reason to doubt that there are circumstances when additional records become available or a different research approach leads to an extension of an existing line. Often, the brick wall situations involve looking for the wrong person, or in the wrong place or at the wrong time. However, by looking at research as always open ended, you could argue that given the proper circumstances, someone really could extend their family line all the way back to Adam.
Back to the question, is there a practical and reasonable end to research? Or can all barriers be overcome? Let's start with a common problem, lack of identity of a father (or even a mother) of a living person. Suppose, the individual was born out of wedlock, and in a not too uncommon case, the father is not identified in any birth record, either because the mother refused to disclose the father or because the mother may not have known who the father was. By the way, I deal with this issue regularly. But, you say, you can still research the mother's line (back to Adam or whatever). But does the identity problem really stop any further research? There may be circumstances where this obstacle to obtaining information has been somehow resolved, through DNA testing or whatever, but what if the paternity issue is more than a few years back in the past? There have been a few highly publicized cases where paternity has been "proved" historically by DNA or other means many years after the fact. But, absent a prominent historical figure, it is unlikely that anyone would commit the resources needed to overcome the lack of historical data.
So, does the lack of identity of a father for a child constitute a practical or even a reasonable limit to further research. My conclusion would depend on the circumstances. In most cases, unless there is a breakthrough in record availability, the lack of identify is a limit to the extension of that particular line. A similar issue exists in the past, depending on the area of the world, with the recordation of maternal surnames. If the mother's family was not recorded, there may be a practical or reasonable end-of-line situation. In some countries, such as China and Japan, records do exist back thousands of years, but in Western Europe, information on individuals, other than royalty, are extremely scarce before 1000 AD.
What I see as a problem with the failure to come to a reasonable end to genealogical research, is that the family doing the research may become fixated on the brick wall problem to the exclusion of any other research. In some cases, it may be realistic to acknowledge lack of identity of a wife's parents, as a reasonable limit to the extension of that particular family line.
Some apparent end of line situations are very likely solvable. For example, the immigration problem, that is, tying the immigrant to his old world country or origin. Although difficult at times, this is an area where additional information may actually help determine the place of origin.
Can I avoid the whole issue by merely tying into one of the diverse royal families and thereby gain the requisite pedigree (again back to Adam)? Well, yes, they did have descendants. But, the old royal pedigrees are not substantiated for the most part. An individual may get some satisfaction from believing that they are descended from royalty, but that is not real genealogy. (My opinion).
What then is real practical limit to records that can be used for constructing a pedigree? No, I do not believe the old Court House burning problem is a practical or reasonable end to research. Yes, records have been lost, but the last time I checked, courthouses were not the only place records were kept.
Yes, there are practical and reasonable limits to the extension of family lines. At some point, all lines reasonably end. Looking at the time, the place and the actual availability of records in general will give the researcher an opportunity to determine if the time and effort might be better spent on other family lines.