During Thomas Jefferson's lifetime, species extinction was a subject of much debate. From Jefferson's papers, Monticello researchers have compiled the primary source references shown below.
1786 December 17. (Jefferson to Charles Thomson). "As he [the creator of the earth] intended the earth for the habitation of animals and vegetables is it reasonable to suppose he made two jobs of his creation? That he first made a chaotic lump and set it into rotatory motion, and then waiting the millions of ages necessary to form itself, that when it had done this he stepped in a second time to create the animals and plants which were to inhabit it? As the hand of a creator is to be called in, it may as well be called in at one stage of the process as another. We may as well suppose he created the earth at once nearly in the state in which we see it, fit for the preservation of the beings he placed on it."
1787. (Notes on the State of Virginia). "Every race of animals seems to have received from their Maker certain laws of extension at the time of their formation. ... It may be asked, why I insert the Mammoth, as if it still existed? I ask in return, why I should omit it, as if it did not exist? Such is the economy of nature, that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken. To add to this, the traditionary testimony of the Indians, that this animal still exists in the northern and western parts of America, would be adding the light of a taper to that of the meridian sun. Those parts still remain in their oboriginal state, unexplored and undisturbed by us, or by others for us. He may as well exist there now, as he did formerly where we find his bones. ... It would be erring therefore against that rule of philosophy, which teaches us to ascribe like effects to like causes, should we impute this diminution of siace [of animals] in America to any imbecility or want of uniformity in the operations of nature. ... Animals transplanted into unfriendly climates, either change their nature and acquire new fences against the new difficulties in which they a replaced, or they multiply poorly and become extinct."
1787 September 20. (Jefferson to Charles Thomson). "It is now generally agreed that rock grows, and it seems that it grows in layers in every direction, as the branches of trees grow in all directions. Why seek further the solution of this phaenomenon? Every thing in nature decays. If it were not reproduced then by growth, there would be a chasm."
1796 November 10. (Jefferson to John Stuart). "I cannot however help believing that this animal [megalonyx] as well as the Mammoth are still existing. The annihilation of any species of existence is so unexampled in any parts of the economy of nature which we see, that we have a right to conclude, as to the parts we do not see, that the probabilities against such annihilation are stronger than those for it."
1799. (A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia). "In fine, the bones exist: therefore the animal has existed. The movements of nature are in a never ending circle. The animal species which has once been put into a train or motion, is still probably moving in that train. For if one link in nature's chain might be lost, another and another might be lost, till this whole system of things should evanish by piece-meal; a conclusion not warranted by the local disappearance of one or two species of animals, and opposed by the thousands and thousands of instances of the renovating power constantly exercised by nature for the reproduction of all her subjects ...."
1803 April 13. (Jefferson's Instructions for Meriwether Lewis (drafted April 13, 1803, and signed June 20, 1803)). "Other objects worthy of notice will be ... the remains & accounts of any [animal] which may be deemed rare or extinct ...."
1803 November 14. (Jefferson to David Williams). "[T]he general desire of men to live by their heads rather than their hands, & the strong allurements of great cities to those who have any turn for dissipation, threaten to make them here, as in Europe, the sinks of voluntary misery."
1804 August 16. (Jefferson to John Page). "[A]ccording to the rules of philosophising, where one sufficient cause for an effect is known, it is not within the economy of nature to employ two."
1811 August 20. (Jefferson to Charles Willson Peale). "I have often thought that if heaven had given me choice of my position & calling, it should have been on a rich spot of earth, well watered, and near a good market for the productions of the garden. no occupation is so delightful to me as the culture of the earth, & no culture comparable to that of the garden. such a variety of subjects, some one always coming to perfection, the failure of one thing repaired by the success of another, & instead of one harvest a continued one thro’ the year."
1818 February 9. (Jefferson to Francis van der Kemp). "... it might be doubted whether any particular species of animals or vegetables, which ever did exist, has ceased to exist."
1823 April 11. (Jefferson to John Adams). "[T]he argument which they [disciples of Ocellus, Timaeus, Spinosa, Diderot and D'Holbach] rest on as triumphant and unanswerable is that, in every hypothesis of Cosmogony you must admit an eternal pre-existence of something; and according to the rule of sound philosophy, you are never to employ two principles to solve a difficulty when one will suffice. ... on the contrary I hold (without appeal to revelation) that when we take a view of the Universe, in it's parts general or particular, it is impossible for the human mind not to percieve and feel a conviction of design, consummate skill, and indefinite power in every atom of it's composition. ... it is impossible, I say, for the human mind not to believe that there is , in all this, design, cause and effect, up to an ultimate cause, a fabricator of all things from matter and motion, their preserver and regulator while permitted to exist in their present forms, and their regenerator into new and other forms. we see, too, evident proofs of the necessity of a superintending power to maintain the Universe in it’s course and order. ... certain races of animals are become extinct; and were there no restoring power, all existences might extinguish successively, one by one, until all should be reduced to a shapeless chaos."
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