“I have endeavoured to show that no absolute structural line of demarcation, wider than that between the animals which immediately succeed us in the scale, can be drawn between the animal world and ourselves; and I may add the expression of my belief that the attempt to draw a physical distinction is equally futile, and that even the highest faculties of feeling and of intellect begin to germinate in lower forms of life.”

Preface; The Sacredness of Human Life
1930s, On the Rocks (1933)
Context: In law we draw a line between the killing of human animals and non-human ones, setting the latter apart as brutes. This was founded on a general belief that humans have immortal souls and brutes none. Nowadays more and more people are refusing to make this distinction. They may believe in The Life Everlasting and The Life to Come; but they make no distinction between Man and Brute, because some of them believe that brutes have souls, whilst others refuse to believe that the physical materializations and personifications of The Life Everlasting are themselves everlasting. In either case the mystic distinction between Man and Brute vanishes; and the murderer pleading that though a rabbit should be killed for being mischievous he himself should be spared because he has an immortal soul and a rabbit has none is as hopelessly out of date as a gentleman duellist pleading his clergy. When the necessity for killing a dangerous human being arises, as it still does daily, the only distinction we make between a man and a snared rabbit is that we very quaintly provide the man with a minister of religion to explain to him that we are not killing him at all, but only expediting his transfer to an eternity of bliss.

Source: Quotes 1960s-1980s, 1980s, Rules and Representations (1980), p. 4.

Light (1919), Ch, XXI - No!

Source: The Geological Evidences of the Antiquity of Man (1863), Ch.20, p. 393
Context: I endeavoured to sketch out (and it was, I believe, the first systematic attempt to accomplish such a task) the laws which govern the extinction of species, with a view of showing that the slow, but ceaseless variations, now in progress in physical geography, together with the migration of plants and animals into new regions, must, in the course of ages, give rise to the occasional loss of some of them, and eventually cause an entire fauna and flora to die out; also, that we must infer, from geological data, that the places thus left vacant from time to time, are filled up without delay by new forms, adapted to new conditions, sometimes by immigration from adjoining provinces, sometimes by new creations. Among the many causes of extinction enumerated by me, were the power of hostile species, diminution of food, mutations in climate, the conversion of land into sea, and of sea into land, &c.

after 2000, Agnes Martin: Between the Lines', 2002

Source: Wicked: The Life and Times of the Wicked Witch of the West

Source: On the Origin of Species (1859), chapter XIV: "Recapitulation and Conclusion", page 484 http://darwin-online.org.uk/content/frameset?pageseq=505&itemID=F376&viewtype=side, in the second (1860) edition

Art Psalms (2008), Let Love Draw the Line

"Do Animals Have Beliefs?" (1979); as quoted in The Case for Animal Rights by Tom Regan (University of California Press, 2004), p. 36 https://books.google.it/books?id=Y0tWjRmxFE4C&pg=PA36.