There is a lot of hogwash being circulated on the subject of the "origins" of morris dancing. Enormous amounts of speculation based on little or no data, faulty assumptions, wishful thinking, and bad logic.

Secondly, not everything that is called "morris dancing" is necessarily related, and some things that are not called "morris dancing" may be. Nomenclature is a dangerous basis for historical theories.

Thirdly, even a particular type of morris dancing probably has multiple antecedents. It's misleading to talk about "the origin".

Having said all that, here's some research findings.

  • There is no reason to believe morris dancing ever had anything to do with pagan fertility rites.

  • There probably was nothing called "morris dancing" in England much earlier than the 15th century. Around then, a form of dance typically called by names like "moreys daunce" was imported from somewhere in Europe as court entertainment. This may have been the dance form (or one of several dance forms) going by names like "morisco" on the continent. The dancers wore colourful, fairly elaborate costumes with pendant sleeves and attached bells. Very little is known about the dances per se although there seem to have been two types, a solo dance, and a dance in a circle around a "maiden" (who could have been a man in women's clothing) for whose favours the dancers compete.

  • By the early 16th century morris dancing had become a fixture of Church festivals. Later in the century, the morris became attached to village fetes, particularly in the springtime. Shakespeare says "as fit as a morris for May Day" and "a Whitsun morris dance." In the process of going from court to church festivals to village festivals, some changes in the dance may have occurred. By this time we have references to dancing with hankies (this might have been a substitute for the pendant sleeves). Will Kemp danced a solo morris from London to Norwich in 1600. There was a brief fad of morris in the theatre. There are frequent references to women morris dancers - one can infer that women's participation in the morris was not uncommon in this era.

  • It has been hypothesised that the morris was largely forgotten under Oliver Cromwell, and that afterward it was "revived" by the expedient of taking the accoutrements of the old morris -- the bells and hankies -- and using them in adaptations of ordinary social country dances. The truth is probably not that simple. Playford's collection of country dances went through several editions during the Protectorate, demonstrating that dance was not as thoroughly suppressed as one might think, but the resemblences between Cotswold morris dances and some of the Playford dances are suggestive of a connection. Some have read this as evidence that the social dances were derived from the morris, but vice versa seems more likely according to today's scholars. In this sense, what was called "morris" in the 18th century may have had very little to do with what was called "morris" in the 16th century.

  • By the mid 18th century in the South Midlands region, morris dancing with bells and hankies was a fixture of the Whitsun ales (village festivals). By this point, the morris was in the hands of common folk who couldn't afford the fancy costumes of a couple centuries earlier, and they were resorting to ordinary clothing decorated with ribbons and flowers. There was a separate variety of morris, called bedlam morris, being done in a swathe from the Welsh border counties through Warwickshire and Northamptonshire down to Buckinghamshire - the bedlam morris seems to have been mainly or exclusively done with sticks.

  • By the late 18th century the bedlam morris had exerted an influence on the Whitsun ale morris, so that the latter often had both stick and hankie dances. As a result of the element of competition in the Whitsun morris ales, the dances often became quite elaborate in their choreography. These were the dances Sharp mainly collected, commonly (though inaccurately) called Cotswold morris, and are what is often thought of as the morris today.

As for sword dances, Northwest morris, molly dancing, the Abbots Bromley Horn Dance, the Derbyshire processional morris, the Welsh Cadi Ha and other such possibly related things, more research is required.