It is a standing joke among people who know Wales that there are only a handful of Welsh surnames (last names), consisting primarily of Jones, Evans, Roberts, Thomas, Williams, and Davies. Among English speakers, these last names are clearly derived from first names. Why is that? Why don’t the Welsh have the huge variety of surnames like the English do?

The answer lies in the moment that the Welsh switched from the patronymic system of names (Sarah ferch Ronald; Carew ap Daniel) where a child’s name contained a first name, then ‘son of’ or ‘daughter of’, and then their father’s name, to a system where everyone in the family had the same surname.

In England, this transition occurred soon after the Norman conquest of 1066.

“Before the Norman Conquest of Britain, people did not have hereditary surnames: they were known just by a personal name or nickname.

When communities were small each person was identifiable by a single name, but as the population increased, it gradually became necessary to identify people further – leading to names such as John the butcher, William the short, Henry from Sutton, Mary of the wood, Roger son of Richard. Over time many names became corrupted and their original meaning is now not easily seen.

After 1066, the Norman barons introduced surnames into England, and the practice gradually spread. Initially, the identifying names were changed or dropped at will, but eventually they began to stick and to get passed on. So trades, nicknames, places of origin, and fathers’ names became fixed surnames -names such as Fletcher and Smith, Redhead and Swift, Green and Pickering, Wilkins and Johnson. By 1400 most English families, and those from Lowland Scotland, had adopted the use of hereditary surnames.”  http://www.bbc.co.uk/history/familyhistory/get_started/surnames_01.shtml

In Wales, this process didn’t begin until after the Norman conquest of 1282. Sometimes a long time after: “In 1292, 48 per cent of Welsh names were patronymics, and in some parishes over 70 per cent …” The key is to understanding Welsh names is that “the stock of Welsh surnames is very small … attributable to the reduction in the variety of baptismal names after the Protestant Reformation.”  https://en.wikipedia.org/wiki/Welsh_surnames

Martin Luther posted his ‘Ninety-five Theses’ in 1517. This page details how the reformation took hold in Wales on a larger scale than in Ireland and other regions of the UK. http://www.tudors.org/as-a2-level/wales-and-the-reformation/

It’s a strange progression to go from religious reformation to everyone in Wales having the last name ‘Evans’!

By contrast, there was a much greater variety of names in Wales in the thirteenth century and earlier.  http://heraldry.sca.org/names/welsh13.html

In comparison, among the English, the tradition of surnames was well established by the 13th century. From the subsidy rolls of 1292, everyone has a surname. “The largest group is formed by local surnames, those derived from place-names. Out of some 800 taxpayers no less than about 350 have names of this type …

Surnames of relationship derived from font-names number about 65, but some are more or less uncertain. Nearly all consist simply of a font-name, as (Reinaud) Abel, (Robert) Baudri, (William) Reyner. The only exceptions are (John) le fiz Michel, (William) fil. Marie. The last is the only indubitable case of a surname having been derived from a woman’s name, but a possible case is (Katherine) Swote. Most of these surnames, were probably patronymic or inherited. But it was common in early London for apprentices to take their master’s surname, or sometimes his font-name, for a surname. A certain case of the latter kind is (Ralph) Miles (Bridge), but probable ones are (Walter)Milis, (Richard) Pentecoste (Bridge), (Geoffrey) Fouq‘ (Walbr), (Richard) Wolmer (Bill).

The remaining surnames are mostly by-names or nicknames. About 130 persons have such names. There are a number of personal appellations, as the English Barn, Brother, Langman, Molling, Shailard, the French Bacheler, Cosin, le Fount, Galopin, Palmere, the German Winterman, perhaps Junkur; names of animals, English such asBulloc, Hog; Bunding, Pecoc; Burbat, Hering; Fros; the French Louet, Motun; Hairon, Partrys; various concrete words such as the English Fot (possibly a font-name), Gut, Heued; Cope, Hod, Punge; Box; Cros, Horn, Knotte; the French Oingnon, Pointel; abstract words, as possibly Leyk, May.

A good many surnames are derived from adjectives, mostly English, as Brun, Dreye, Dun, Flinthard, Gode, Grete, (le) Long (Lung), le Rede, Saly, Scharp, Skelfol, pwrgode, le Wyte, but some French, as (le) Blund, Curteys, le Gay, Hauteyn, la Jouene, le Megre, le Rous, le Simple, Sotel. Bahuvrihi formations are the English Godchep, Hauekeseye, Langpurce, Lythfot, perhaps Capriht, Trigold, the French Deusmars, Trenmars. Skipop is a formation of the type Shakespeare.”  http://www.british-history.ac.uk/report.aspx?compid=31906#s2