I am doing some informal research on the number of citations indexed by ISI for paleoanthropologists. After quite a lot of searching, I have come to an approximate list of the top ten. This is after a survey of around thirty that I thought likely to have over 500 citations, so I think the top ten is pretty secure. If you are a paleoanthropologist curious about your place on the list, let me know, and I'll tell you if I have the numbers.
These numbers potentially change daily, so they should be viewed as a snapshot of the field during around two weeks of time. A recheck showed that some had increased during the time of the survey.
The methods are simple: a cited reference search on ISI with the full initials used in publications, added to a second search with only the first initial. Less inclusive searches required some vigilance, because of the potential to confuse different people with irrelevant (for anthropology) references.
Certain names are very difficult to search. For example, TD White is shared by at least four distinct scientists with substantial publication records, including one with rather more citations and another who studies gait in vertebrates! So even the journal name is not sufficient to sort them out. For this one (and variant T White) I carefully picked through abstracts to make sure that the correct one was cited. Alan Walker was a nightmare, with nearly 3000 publications credited an "A Walker" of one kind or another.
It should be noted that citations are a very imperfect measure of research productivity or influence. First, citations are heavily biased toward a few high-profile publications. Especially authors who have review-type papers in Science (and to a lesser extent, announcements in Science and Nature) have a citation advantage. Second, many of these scientists work collaboratively, and so a single paper may count toward the total of two or more authors. There is certainly no concept of "fairness" to be placed on this particular ranking, since a single paper may reflect many years of research effort or only several days. In that sense, it is more of a popularity contest, albeit one that reflects the scientific priorities of the field.
Also, authors who are (delicately put) more advanced in their careers have a notable relative disadvantage in these figures, because of the increasing number of journals tracked by ISI over time. To put it in perspective, when I did this same exercise last year, the leader had around 1100 citations (and Stringer was substantially lower on the list). I don't think there have been that many new references in 2004; I think instead that the citation listings have become more comprehensive. For example, this year they seem to include many more citations from books, edited volumes, foreign journals, and theses. At any rate, scholars who publish extensively in such sources are sure to be underrepresented in the citations.
With all those caveats in mind, it seems to me a remarkable coincidence that the top of the list should be so close in citations. Many of them began their careers around the same time, but I think that more than that is required. My guess is that around over 1000 citations, we are reaching as complete a saturation of paleoanthropology as one can achieve. That might bump a bit higher if someone has key articles in several distinct topics. Also, cannibalizing one's own work appears to face very low risk: I have noticed many publications that are basically carbon copies of each other all having high citation rates, because different people read them, or cite the "updated version."
The leaders owe their high citation numbers to the degree to which they draw attention from other fields. For example, Stringer and Wolpoff both have high citation rates in human genetics. The same is true of Walker for fossil primates and Holloway for psychology.
Right now I stand at 133 citations. It may be awhile before I crack the top ten....