He was among the first to attempt a biological definition for the concept of species, as "a group of morphologically similar organisms arising from a common ancestor".

[10] Ray kept writing books and corresponded widely on scientific matters, collaborating with his doctor and contemporary Samuel Dale.

[12] At Cambridge, Ray spent much of his time in the study of natural history, a subject which would occupy him for most of his life, from 1660 to the beginning of the eighteenth century.

[8][9] When Ray found himself unable to subscribe as required by the Act of Uniformity 1662 he, along with 13 other college fellows, resigned his fellowship on 24 August 1662 rather than swear to the declaration that the Solemn League and Covenant was not binding on those who had taken it.

[13] From this time onwards he seems to have depended chiefly on the bounty of his pupil Francis Willughby, who made Ray his constant companion while he lived.

[5] They travelled extensively, carrying out field observations and collecting specimens of botany, ornithology, ichthyology, mammals, reptiles and insects.

Ray himself published an account of his foreign travel in 1673, entitled Observations topographical, moral, and physiological, made on a Journey through part of the Low Countries, Germany, Italy, and France.

From this tour Ray and Willughby returned laden with collections, on which they meant to base complete systematic descriptions of the animal and vegetable kingdoms.

[15][10] In 1667 Ray was elected Fellow of the Royal Society,[15] and in 1669 he and Willughby published a paper on Experiments concerning the Motion of Sap in Trees.

The plants gathered on his British tours had already been described in his Catalogus plantarum Angliae (1670), which formed the basis for later English floras.

Instead, Ray considered species' lives and how nature worked as a whole, giving facts that are arguments for God's will expressed in His creation of all 'visible and invisible' (Colossians 1:16).

Despite his early adherence to Aristotelian tradition, his first botanical work, the Catalogus plantarum circa Cantabrigiam nascentium (1660),[19] was almost entirely descriptive, being arranged alphabetically.

The latter he divided by life forms, e.g. trees (arbores), shrubs (frutices), subshrubs (suffrutices) and herbaceous plants (herbae) and lastly grouping them by common characteristics.

[25] His first publication, while at Cambridge, was the Catalogus plantarum circa Cantabrigiam nascentium (1660), followed by many works, botanical, zoological,theological and literary.

[32] The John Ray Initiative (JRI) is an educational charity that seeks to reconcile scientific and Christian understandings of the environment.

John Ray's writings proclaimed God as creator whose wisdom is "manifest in the works of creation", and as redeemer of all things.

JRI aims to teach appreciation of nature, increase awareness of the state of the global environment, and to promote a Christian understanding of environmental issues.