Spencer's term (1864) 'survival of the fittest' is simply a re-hash of Matthew's (1831, p. 387) original phrase 'selection by the law of nature' , which Darwin (1859) shortened to 'selection by nature' on page 224 of the Origin of Species. Spencers re-hash is more elegant but less precise than Matthew's (1831, p.385) original prose:
'Nature tests their adaptation to her standard of perfection and fitness to continue their kind by reproduction.'
Matthew (1831) wrote also about the natural process of selection on pages 364-365 using examples of fierce strength, cunning and swiftness being present in naturally selected species:
'This law sustains the lion in his strength, the hare in her swiftness, and the fox in his wiles.'
Matthew (pp 307-308) wrote further of the survival of 'the best circumstance suited for reproduction', which is a far more precise phrase than Spencer's, which has been wrongly taken by non-experts to imply that the most athletic survive in competition.
Moreover, Matthew uses his phrase in the context of his original Artificial versus Natural selection analogy of Differences, that Wallace used in his 1858 Ternate paper, Darwin used in his unpublished essay and then to open Chapter One of the Orign of Species (Darwin 1859).
Matthew was the first to use the powerfully simple Artificial versus Natural Selection Analogy of Differences to explain the complexity of natural selection. This is probably the most important explanatory analogy ever published in the history of humanity. Loren Eiseley (1979) had earlier discovered that Darwin's unpublished (1844) replicated Matthew's (1831) plants grown in nurseries versus those growing wild analogy of differences to explain the operation of natural selection. What none before me picked up on is that Darwin (1859) opened Chapter 1 of the Origin of Species with Matthew's unique explanatory analogy:
'When we look to the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us, is, that they generally differ much more from each other, than do the individuals of any one species or variety in a state of nature. When we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, I think we are driven to conclude that this greater variability is simply due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent-species have been exposed under nature.'
Matthew (1831) had earlier written on page 308 - in the main body of his book: