9. Children of deaf parents are far more likely to be deaf than children of hearing parents.
10. The great majority of the children of deaf parents, however, are able to hear, the proportion of those who are not being small.
11. The likelihood of deaf offspring is not necessarily greater when both parents are deaf than when one is deaf and the other hearing.
12. The liability to deaf offspring depends in the greatest degree upon the presence or absence in the parents, deaf or hearing, of deaf relatives, and, to a less extent, upon whether or not the existing deafness is congenital--being especially great under a combination of these two conditions.
13. Action in respect to marriages of the deaf likely to result in deaf offspring seems for the present rather to be limited to moral forces.
14. Congenital deafness appears, from all the evidence, to be decreasing relatively among the population, though probably only at a very slow rate.
15. Finally, with respect to our original inquiry, it is to be said that there are no indications that deafness will disappear from the human race within any time which we can measure; and hence that the deaf are to be in society not only for a season, but for a period apparently as yet indefinite. Nevertheless the situation is not without encouragement. From the data in our possession regarding deafness as a whole, it seems certain that deafness is not on the increase relatively among the population. From our knowledge concerning adventitious deafness, the probabilities are that, if anything, it is decreasing; while the evidence as to congenital deafness is that it is decreasing. It is likely, then, that deafness in general is tending to decrease; and we are thus justified in believing that the number of the deaf will in time become less.
[15] Moreover, later censuses are probably taken more thoroughly than former, with a consequent discovery of a larger number of the deaf; while at the same time greater care is employed in preparing the later censuses, with the more rigorous elimination of doubtful cases, all in some measure, however, tending to even up the differences. On the difficulty of making comparisons of the censuses of the deaf, see Special Reports, pp. 66-69; _Annals_, li., 1906, p. 487.