The capacity of improvement in plants and animals, to a certain degree, no person can possibly doubt.  A clear and decided progress has already been made, and yet, I think, it appears that it would be highly absurd to say that this progress has no limits.  In human life, though there are great variations from different causes, it may be doubted whether, since the world began, any organic improvement whatever in the human frame can be clearly ascertained.  The foundations, therefore, on which the arguments for the organic perfectibility of man rest, are unusually weak, and can only be considered as mere conjectures.  It does not, however, by any means seem impossible that by an attention to breed, a certain degree of improvement, similar to that among animals, might take place among men.  Whether intellect could be communicated may be a matter of doubt:  but size, strength, beauty, complexion, and perhaps even longevity are in a degree transmissible.  The error does not seem to lie in supposing a small degree of improvement possible, but in not discriminating between a small improvement, the limit of which is undefined, and an improvement really unlimited.  As the human race, however, could not be improved in this way, without condemning all the bad specimens to celibacy, it is not probable that an attention to breed should ever become general; indeed, I know of no well-directed attempts of this kind, except in the ancient family of the Bickerstaffs, who are said to have been very successful in whitening the skins and increasing the height of their race by prudent marriages, particularly by that very judicious cross with Maud, the milk-maid, by which some capital defects in the constitutions of the family were corrected.

It will not be necessary, I think, in order more completely to shew the improbability of any approach in man towards immortality on earth, to urge the very great additional weight that an increase in the duration of life would give to the argument of population.

Many, I doubt not, will think that the attempting gravely to controvert so absurd a paradox as the immortality of man on earth, or indeed, even the perfectibility of man and society, is a waste of time and words, and that such unfounded conjectures are best answered by neglect.  I profess, however, to be of a different opinion.  When paradoxes of this kind are advanced by ingenious and able men, neglect has no tendency to convince them of their mistakes.  Priding themselves on what they conceive to be a mark of the reach and size of their own understandings, of the extent and comprehensiveness of their views, they will look upon this neglect merely as an indication of poverty, and narrowness, in the mental exertions of their contemporaries, and only think that the world is not yet prepared to receive their sublime truths.