Elaine Morgan: Author whose most celebrated works expounded the Aquatic Ape Theory of evolution

Elaine Morgan, author of the international best-seller The Descent of Woman, a feminist view of evolution, enjoyed a brief celebrity shortly after its publication in 1972, mainly on account of her brilliantly argued thesis that humans had their origins in the sea and that women are not biologically or socially inferior to men. But she earned a living by writing scripts, mainly serials and documentary dramas, for television – work for which she never received her full meed of praise.

Perhaps her best-known adaptation was that of Vera Brittain's Testament of Youth (1980), which reflected her own feelings about war and women's struggle for education, but she also wrote many documentaries which were widely admired for the skills she brought to the small screen. They included treatments of Anne Frank, Madame Curie and, to great acclaim in her native Wales, The Life and Times of David Lloyd George – starring Philip Madoc as the eponymous statesman – and a television version of Richard Llewellyn's novel How Green Was My Valley.

Morgan was born in 1920 in Hopkinstown, a mining village at the lower end of the Rhondda Valley. Her father was a colliery pumpsman who, in the locust years of the 1920s, was often unemployed. From the widespread poverty and industrial strife of the period she learned the Socialism to which she would remain committed for the rest of her life.

After winning an Exhibition to Oxford in 1939, she read English at Lady Margaret Hall; but disheartened by having to write critically about literature, she put off all thought of being a writer for more than a decade. Her time as an undergraduate was largely spent debating working-class conditions of which she had first-hand experience. In 1942 she succeeded Anthony Crosland and Roy Jenkins as chairman of the Oxford University Democratic Socialist Club.

At her father's death towards the end of her first term, her mother insisted that she stay on at Oxford, devising ways of earning enough money to keep her there. In her autobiographical play, A Matter of Degree, Morgan explored the tensions felt by a working-class student at Oxford. Of her own dilemma she later commented, "I never felt much of a conflict as to whether I should remain with my own class and keep their outlook in life or identify with the other lot. I always liked the Welsh end more."

She took a job as a lecturer with the Workers' Educational Association and then, in 1945, settled in Mountain Ash in the Cynon Valley with her husband, Morien Morgan. He taught French at the Boys' Grammar School in Pontypridd where, among us sixth-formers, he cut a dashing figure for having fought in defence of the Spanish Republic. The couple were often to be seen on CND marches and Elaine once shared a platform in Cardiff with Bertrand Russell.

Her formidable intellectual gifts were displayed in all that she wrote. In The Descent of Woman she took on not only the Book of Genesis but also anthropologists as diverse as Darwin, Robert Ardrey, Konrad Lorenz and Desmond Morris, reserving her most closely argued strictures for Freud, whom she saw as a major barrier to women's emancipation.

The book had its source in a controversial thesis propounded in 1960 by Alister Hardy, Professor of Marine Biology at Oxford, that many of the characteristics differentiating humans from other primates date from a prehistoric period of aquatic adaptation. Feminists welcomed its emphasis on the role and needs of females, as a challenge to theories leaning towards a notion of "man the hunter" – but some male professional scientists were scathing about it.

After the book's success (it was translated into 25 languages), Morgan went on to write three more in which she posited new and thought-provoking theories of human evolution: The Aquatic Ape (1982), The Scars of Evolution (1990) and The Descent of the Child (1994).

Hardy's theory – based on the observation that the subcutaneous fat of humans more closely resembles that of sea mammals than of grassland primates – was derided and largely ignored until the appearance of Morgan's books. Then, in 1995, Professor Phillip Tobias, one of the most eminent proponents of the hypothesis that man had originated on the savannah of Africa, announced in a lecture that it was mistaken.

Since then, the Aquatic Ape or Riparian theory as formulated by Hardy and elaborated by Morgan has been given a good deal of favourable publicity, notably in New Scientist, The Observer and the BBC Wildlife Magazine. The theory also had an influence on Margaret Drabble's novel The Sea Lady (2006). In 2005 she published Pinker's List, a spirited demolition of the theories of the right-wing Steven Pinker.

Falling Apart (1976) is an equally original and indignant study of the rise and decline of urban civilisation from several viewpoints – biological, sociological, psychological, political, economic and historical, but always from the angle of an outsider rather than a city-dweller. Her main concern was to find "cleaner and greener" alternatives to urban civilisation; many of her insights were derived from living in one of the most polluted post-industrial valleys of south Wales.

Among her arguments were that urbanisation is the same under capitalism and communism; that market forces are now beginning to be inimical to the growth of cities; that the great metropolitan centres are no longer the prime generators of wealth but are moving into a parasitical stage; and that the solution to the cities' problems will have to come from outside because city-dwellers are no longer capable of addressing them.

In between writing her books on evolutionary theory, Morgan lived on her income from television. Her first plays had been for the stage, but none of them was a hit. Among her first successes on the small screen were three episodes of Inspector Maigret, followed by a dozen of Dr Finlay's Casebook, for which, there being so few novels by A J Cronin on which to base the series, she had to devise the story-lines herself. "The marvellous thing about Finlay," she said, "was that you could say anything and people were not offended: I dealt with syphilis in one and euthanasia in another."

This last remark was typical of her forthright, but always genial manner, and her willingness to explore in her writing, from a rigorously feminist point of view, themes which provided her with opportunities to challenge the bearded orthodoxies.

Meic Stephens

Elaine Morgan (née Floyd) , writer: born Hopkinstown, Glamorgan, 7 November 1920; married 1945 Morien Morgan (deceased; three sons); died 12 July 2013."