Dreadlocks are actually knitted/matted hairs.

Brutal dreadlocks

Dreadlocks are actually knitted/matted hairs.

This can happen spontaneously as a result of not combing the hair which is long enough to knit – in this form the dreadlocks have probably existed since the Neanderthals and Cro-Magnons walked the earth more than 35000 years ago, till today. 

The dreadlocks can also be made purposely by knitting the hairs together with various tools.

Sometimes, only a preparation like wax or butter mixed with ochre and herbs is used, but it only works with very curly African hairs.

When the latter practice started no one can actually say. Presence of people with dreadlocks throughout the past is evident on all the continents and among many uncivilized communities inhabiting the globe, but also among various civilizations, past and present.

Many sources claim that the first written mention of dreadlocks comes from the Veda scriptures of India (the earliest piece is almost 4 thousand years old).

 

Ancient Egypt is also one of the earliest known societies to wear locks. There have been many artifacts such as statues and locked wigs; and even mummified bodies of pharaohs with locked hair have been discovered in recent years. The Egyptians saw appearance as an indication of social status and believed that dreadlocks made them appear more powerful.

Ancient Asian emperors wore them. 

Writings about dreadlocks can even be found in the Christian Bible.
Different forms of dreadlocks have always been present among many tribes on the African continent. More recently, the Mau Mau tribe wore dreadlocks to intimidate the colonizers of Kenya in East Africa.

The aborigines of Australia, indigenous people of the South/North American continents, the various pagan tribes of Europe, Germanic tribes, the Celts, the barbaric tribes on Balkan...

The colonization was started in Europe by Romans and was continued by Christians and various kingdoms which in the end evolved to national states, following the suppression of the pagan tribes of Europe, and the destruction/erasing of their cultures. Afterwards the same plague spread out on all other continents.

For many of the colonized cultures, the dreadlocks (often accompanied with tattoos, body paintings, piercing (and many other forms or ornamentations and jewelry)) had symbolic value. Since the beginning of the colonization, they were considered obnoxious and savage by Christians, and had to be eradicated as a part their non-Christian identity.

The same principle was used on slaves kidnapped from Africa and brought to America and Europe. 

The presence of this kind of mentality is still evident, especially among Christian/Muslim/Jewish and other conservative communities, and upper class or yuppie scum - and especially among the police around the globe.

That is probably the reason why the dreadlocks are not rarely accepted as a symbolic element of various subcultures and movements round the globe of which some were explicitly countercultural or political, or were just flirting with this sort of ideas.

In the late 70s and 80s, with commercialization and popularization of reggae music by figures like Bob Marley and Eddie Grant, among others, the dreadlocks became popular among the followers and present in pop culture.

This popularization also brought with it a lot of misconceptions like: the dreadlocks are only for black people, all the people with dreadlocks smoke and deal marihuana, the dreadlocks are the symbol of BlackPride racism... and so on, and so on...

Nowdays the dreadlocks are popular among different subcultures and movements. The punks, crustys, goths, hippies, trancers, travelers, squatters, primitivists, rastafarians... have worn them very often,

 and traditionally the dreadlocks are still worn by Sadhus ("holy men") in India, the Somali, the Galla, the Maasai, the Mau Mau, the Kau, the Ashanti, the Fulani, the Aborigines, the New-Guineans... 

The term Dreadlocks originates from Jamaica in the 1950s as a derogatory term - the "Young Black Faith", an early sect of the Rastafari which began among the marginalized poor of Jamaica in the 1930s, ceased to copy the particular hair style of HaileSelassie I of Ethiopia and began to wear locks instead. It was said that they looked 'dreadful' with their locks, which gave birth to the modern name "dreadlocks". 

Different theories exist about the origin of dreadlocks on Jamaica. Some sources trace them back to Indians who arrived to Jamaica to work as indentured laborers in the late 19th century. Others believe the first Rasta dreadlocks were derived from the "dreaded locks" of the Mau Mau, largely Kikuyu protonationalist, insurgency against British colonialism in 1940s Kenya.

Anyhow, the term is coined and is embraced around the globe. After all the dreadlocks still look dreadful to all the conservative people.