He studied anthropology at the London School of Economics and Leiden and is most known for his extensive fieldwork in East Indonesia with the Nuaulu people of Seram.
He has recently embarked on a series of major studies of indigenous knowledge and of the consequences of deforestation in parts of Indonesia and in Brunei.
Ellen has been carrying out ethnobiological fieldwork in eastern Indonesia since the early 1970s, working variously with the Nuaulu people of Seram (with whom he did his doctoral dissertation); on the islands of Sulawesi, Gorom, Seram Laut, Banda and Ambon-Lease; plus some addition fieldwork into the social impacts of logging at Brunei (1991–1994).
He implores conservationists to take indigenous knowledge into account and form a judgment based on evidence for that particular situation and not generalisation (Ellen, 1993).
Empirical knowledge of plants and animals and its broad understanding allows them to comfortably co-exist together and gives way to claims of mutual causation that gives rise to a complex notion of nature He includes that although uncut forest is recognised by Nuaulu as a single entity, it contrasts in different ways with other land types depending on context.
This paper will cover some of Ellen's more recent publishing (ranging from 1997 to 2006) in Seram, Eastern Indonesia and West Java.
As seen through many of Ellen's works, the detailed emphasis on the emic view, and the local knowledge are not only the most important but also give agency to the people using that environment.
Ellen's article "The Contribution of Paraserianthes (Albizia) falcataria to Sustainable Swidden Management Practices among the Baduy of West Java" published in 2000, the Baduy, which maintain their cultural identity through swidden agriculture, also understand to maintain their traditional way of life they must integrate cash crops to sustain themselves.
His findings have informed the studies of subsistence behaviours, the social impact of deforestation, inter- island trade and questions the relationship between nature and culture.
In response to environmental stress, or instability such as political conflict or economic hazards he found that traditional knowledge enables local populations to cope.
Ellen helped renew interest in the study of classification with his book "Categorical impulse: Essays on the Anthropology of classifying behavior”(2008).
His point being that in regards to the classifications of animals made by the Nuaulu people, one must pay attention to different types and contexts of variation.
According to Ellen, “In a single body of data there may be variation according to many criteria which are often cross-cutting and reinforce each other irregularly.”(1979: 337) There are various reasons and ways people classify and categorise as a result of both culture construction and the cognitive approach.
Ellen states what he believes to be inevitable is the fact that the “products of classifying behavior reflect the immediate social conditions of the situations in which they are used”(1979: 337).
In other words, factors such as environment, culture, society and the state in which they exist are heavily influential on the way people classify things.