Origin of Surnames
"Throughout history humans have been known by more than one name to distinguish them from other people with the same name. As societies became more complex or were colonised by more complex societies these distinguishing names became fixed and were passed on to the next generation. The nature of the surnames depends on what was important to the society at the time surnames were adopted. Thus hunter-gatherer societies often distinguished individuals by an event, a characteristic or a religious connotation. More technically advanced cultures with a settled society typically derived surnames from occupations, social status or place of residence. Surnames derived from a father's name are common, particularly in societies that were less developed when they adopted surnames."
Origins of "Ralston"
According to Forebears, Surname DB, House of Names, and Behind the Name, there are several possible origins of the many varieties of the name Ralston, all based on place names. Most prominent is from Scotland, but there were many places in England with similar names that might or not have been the origin of some of the people having a similar surname today. British History Online lists several places in England with similar names. Shown below are the places most frequently sited in surname histories as found on the internet. This information is not necessarily true, but the suppositions of various researchers.
Bruce Ralston of New Zealand, a genealogist and researcher of the Ralston lineage, has made observations regarding the Scottish origin of the name, which are shown following in blue.
Ken Rolston, born in New Zealand, currently of England, a genealogist and researcher of the Ralston/Rolston lineage, has made observations regarding the English origin of the name, which are shown following in red.
- From the lands or barony of Ralston near Paisley, Renfrewshire. The Ralstons "of that Ilk" are descended from the Mac Duffs, Thanes or Earls of Fife, one of whom had a son Ralph. The latter, obtaining a grant of lands in Renfrewshire, called them after his own name, Ralplis-toune. In process of time, his descendants, continuing on the same estate, wrote themselves De Ralphstoune, or, by softened pronunciation, Ralston.    
Ralston is a place in Renfrewshire (Lanarkshire until 1404), on the eastern outskirts of Paisley. There is a location of the same name near Loudon in Ayrshire, which may cause confusion in interpreting some of the medieval records. In both cases there is a strong connection with the Stewart family.
The word consists of two parts: a given or Christian name and a descriptive suffix, ‘ton’.
The given name is Ralph [written as Rawfe and could be pronounced 'Raw']. There is just not enough documentation to say who this Ralph was. The likelihood is he was someone of enough rank to have leased land in the mid to late 12th century from the new landowner, Walter FitzAlan, the Senschal, or Steward, who came to Scotland in 1142 with King David I. David gave Walter land around Renfrew, Paisley and Lochwinnoch, and he also built considerable holdings through northern Ayrshire.
The suffix is the Old English word 'ton' or 'tun', meaning farm or settlement. It is common in placenames throughout the British Isles.
In England, the name Ralston was rare and is seldom found in primary records.
- From a geographic locality of Rollestyon (or Rolleston) (in the Domesday Book, Roolfeston), a parish in Staffordshire, in the West Midlands of England.     I have never seen the variant names Rollestyon or Roolfeston applied to the parish or manor. It was early named Rolvestune or Rolveston. Sometimes written nowadays as Roluestune, but be aware that the U and the V were written the same in those days and were effectively interchangeable.
- Rolleston*, a chapelry, in the parish and union of Billesdon, hundred of Gartree, S. division in Leicestershire.    I have never found a family named Rolleston that derive from this manor in Leics.
- Rolleston*, a parish, in the union of Southwell, partly in the N., and partly in the Southwell, division of the wapentake of Thurgarton, S. division of Nottinghamshire.    This manor of Rolleston in Notts gave rise to a family named de Rolleston, soon after Domesday. They had no connection with the Rolleston manor or family of Staffs. This Notts manor (one of 3 in Rolleston) passed to the Neville family with the marriage to Jollanus de Neville, of Amfilisia de Rolleston, possibly daughter of Benedict de Rolleston about 1305. A number of related Rollestons continued to hold portions of land or perhaps tenancies in the parish. From this family I believe were derived the Rollestons at Beverley, Yorks, prominent merchants and aldermen and clergy in the town, through to at least 1450.
- From a geographical locality of Roulston (or Rowston), a parish in Lincolnshire. Rowston St Clement is an Ancient Parish; the church was built in the 13th century and restored subsequently in 1741.    There is no known family of the name from there.
- From a small village called Rolstone in Somersetshire, site of the Rolstone Standing Stone (Menhir).   There were Rollestons in the west country (Cornwall, Devon, Somerset) from the 1200’s or earlier, but my opinion is that the first of them may have come originally with one of the Ferrers family from Staffordshire. There is no evidence of the Rollestons/Rolstons etc name being derived from one of the placenames, indeed I consider that the opposite may have occurred, that farms were named from one of the early family individuals.
- From a hamlet Rowlston. in the parish of Mappleton, union of Skirlaugh, N. division of the wapentake of Holderness in the East Riding of Yorkshire. "This place, in Domesday Book called Roolfestone, belonged in the 15th century to a family of the local name, and, after passing through several other families."    The Rolleston family who may have been briefly associated with it were from Beverley.
- Rowlstone in Herefordshire, near the Welsh border, a parish on the Monmouthshire border of the county 11 m. S.W. of Hereford. The church is the principal monument.   There were a few individuals surnamed Rolleston who were recorded in the Worcester/Herefordshire area, but there is no evidence of a family derived from there.
One cannot assume that because their particular variation of Ralston spelling matches or is close to the name of a particular location, that their origins are there. Families that emigrated to Ireland, America, Australia, New Zealand, etc., often changed the spelling to what was locally accepted.
* House of Names asserts that families of this place had origins in Staffordshire.
SOURCES https://forebears.io/surnames/  http://www.surnamedb.com/Surname/  https://www.houseofnames.com/  https://surnames.behindthename.com  https://www.british-history.ac.uk/