No article yet exists on the topic of species extinction, the subject of much debate during Thomas Jefferson's lifetime. Below are primary source references to extinction in Jefferson's papers compiled by Monticello researchers.
Primary Source References
1786 December 17. (Jefferson to Charles Thomson). "As he [the creator of the earth] intended the earth for the habitation of animals and vegetable is it reasonable to suppose he made two jobs of his creation? That he first made a chaotic lump and set it into rotary 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 and 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? 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. (Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed King 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 vanish 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 renovated power constantly exercised by nature for the reproduction of all her subjects..."
1803 June 20. (Jefferson to Meriwether Lewis). "Other objects worthy of notice will be...the remains or accounts of any [animal] which may be deemed rare or extinct."
1803 November 8. (Jefferson to David Williams). "The general desire of men to live by their heads rather than their hands, and 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). "According to the rules of philosophizing, when one sufficient cause for an effect is known, it is not within the economy of nature to employ two."
1811 August 20. (Jefferson to John Stuart). "I have often thought that if heaven had given me not see, that the probabilities against such annihilation are stronger than those for it."
1818 April 11. (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). "The 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 perceive 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 to 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 existence might extinguish successively, one by one, until all should be reduced to a shapeless chaos."