species must [now] be part of the regular and constant order of Nature’ (62). 
Lyell had therefore reached a highly satisfactory conclusion without recourse to 
cosmological hypothesis, or to imaginary tendencies, while avoiding any alliance 
with materialistic lines of thought. He was able to prove that the extinction of 
species was a natural process, brought about by the operation of natural causes 
constantly in action.
 

Conditions within a given geographical region, or even within a limited zone, 
were kept in a steady state by the agency of numerous factors - organic and 
inorganic - which produced the ‘balance of nature’. But a modification, though 
slight, suffered by a single element responsible for the conditions of 
equilibrium could have a chain of effects on beings which were directly or 
indirectly related to the agent which had been modified. Man himself, for 
instance, by eliminating some dangerous species, had caused the extinction of 
several animal tribes. Fleming had touched upon this subject in a paper 
published in the Edinburgh new philosophical journal, where he showed how the 
progress of civilization had induced the disappearance of several species 
formerly inhabiting the British Isles (63). There were not only instances of 
animals which had disappeared as a consequence of the development of human 
society in the first period of human life on earth ; a striking example had 
occurred in recent times of the complete extinction of a species, the Dodo, or 
Dronte, which had been firmly established in its station, when the first Dutch 
explorer visited the island of Mauritius. In a few decades the animal completely 
disappeared, so that some naturalists even doubted whether it had ever existed 
(64). To those who objected that the extinction of the Dodo was brought about by 
the action of man, Lyell repeated that the action of man did not constitute an 
exception in the economy of nature. The contemplation of the causes of change in 
terms of population dynamics, Lyell concluded, allowed the inference that their 
continuous action would modify the state of organic creation in the course of 
ages (65).
 

This example was chosen in order to show the working of his model, and was 
designed to prove the validity of his theory, and its superiority over 
Lamarckism and every possible revival of Lamarckism. Lyell considered the case 
where species were limited in their territorial expansion by the unfavourable 
temperature of surrounding localities. Lyell applied to this example the 
approach followed by de Candolle in the case of plants living in different 
soils, and remarked that with a slight change of climate, and a lower 
temperature in a zone, the species favoured by a higher temperature would be 
weakened, and might be destroyed by a neighbouring species which could easily 
tolerate a lower temperature. A species would never have been allowed to change 
and modify itself according to the changed condition, but would have been 
eliminated by competing forms. Lyell's model was therefore designed to provide a 
definitive refutation of Lamarckism (66). 

(62) C. Lyell, Principles, ii, 141.

(63) J. Fleming, ‘Remarks illustrative of the influence of society on the 
distribution of British animals’, Edinburgh new philosophical journal, 1824, II, 
287-305.
 

(64) For some remarks on the dodo, see G. B. Brocchi, op. cit. (62), p. 236 ; G. 
Cuvier, ‘Notes sur quelques ossemens qui paraissent appartenir au dronte, espèce 
d'oiseau perdue seulement depuis deux siècles’, Bulletin des sciences 
naturelles, 1830, 17, 122-5 ; Bory de Saint Vincent, ‘Dodo’, Dictionnaire, 1823, 
iii ; J. S. Duncan, ‘A summary review of the authorities on which naturalists 
are justified in believing that the Dodus, Dodus ineptus, Linn, was a bird 
existing in the isle of France or the neighbouring islands, until a recent 
period’, Zoological journal, 1828, 3, 554-66.
 

(65) C. Lyell, Principles, ii, 156-7.

(66) A- P. de Candolle, op. cit. (45), p. 27 ; C. Lyell, Principles, ii, 174-5.