Brooks delivered a paper at a meeting of the American Association for the Advancement of Science AAAS in that asserted first-cousin marriage led to birth defects among the children of such unions. Alexander Graham Bell, best known for inventing the telephone, also waded into the debate.
He suggested introducing legislation to ban consanguineous marriages in families with deaf-mute members so that the condition would not be inherited by children of such marriages. From to , the average person was fourth cousins with their spouse, according to the study. By , the average person was married to their seventh cousin.
The researchers believe that today, many couples are 10th to 12th cousins. The data on consanguineous marriage in the U. Some states allow first-cousin marriages only if the couple can't have children because they are too old or one of the parties is found to be infertile. When you look past first cousins, there are a number of prominent Americans who married more distant cousins.
President Franklin Roosevelt was married to his fifth cousin, once removed. Bittles expects the number of cousin marriages in the U. Load more comments. Search Search. The table of results is as follows The columns of observations show how very unsatisfactory the collectors consider these results. From various circumstances, it appears that the results from Earlswood, Hatton, and the West Riding Asylums are considerably more trustworthy than the others.
Including, then only these three asylums, it appears that, out of 2, patients, 90 or 91 were offspring of first cousins, that is 3. The fact that this agrees pretty closely with the 3. At Hanwell, where also there were some circumstances leading one to believe in tolerable accuracy, the percentage is very small, and this agrees well with what I should have been led to expect, from the small percentage of cousin marriages I found in London, by the methods of the first part of this paper.
It is to be observed, however, that there were twelve cases reported of doubtful consanguinity. It will be seen that the percentage of offspring of first-cousin marriages is so nearly that of such marriages in the general population, that one can only draw the negative conclusion that, as far as insanity and idiocy go, no evil has been shown to accrue from consanguineous marriages. The methods of the first part of this paper throw no light on the question as far as concerns Scotland.
But, whatever the value of these statistics may be, the opinion of prominent medical men, who have had especial advantages of observation, and are many of them also men of science, cannot be without interest. Dr Crichton Browne writes to me that the investigation was impossible in the case of idiots, except through the medium of the parents. Hereditary diseases and cachexiae are much more likely to be shared by cousins than by persons who are in no way related… and these are transmitted with more than double intensity when they are common to both parents… They seem to be the square or cube of the combined volume… Even healthy temperaments, when common to both parents often come out as decided cachexiae in the children.
I fear, however, that I must leave this to some hands more skilful than mine. Howden thus disagrees with Dr. Crichton Browne, who, I take it, would maintain that, in insanity, two plus two makes more, and not less, than four.
Lauder Lindsay is of opinion that the ill-effects of cousin marriage, including insanity, are much less than represented. Several of my correspondents expressed a belief that consanguinity of parents was more potent in producing idiocy than insanity. The results from Earlswood do not seem, however, to confirm this, and here the results sent seemed peculiarly trustworthy.
I had intended to pursue my inquiries in hospitals and asylums for other diseases, but the attempt which I made with respect to deaf mutes has shown me that the difficulties which arise are so great that it is almost useless to persevere in this course any further. I will now give the results which I have collected.
The first return relates to the College for the Blind at Worcester. The results were communicated through the kindness of the Rev.
Robert Blair and Mr. The college is small, and only 20 cases are recorded, and particulars of each case were sent. Of these, 20, the offspring of first cousins were one, and of second cousins one case of 2 brothers.
Of the 20 cases, 2 were due to accidents. Thus, out of 17 families, there was one case of offspring of first cousins. Scott, of Exeter, has informed me that out of families, in which there were children born deaf and dumb, there were 7 cases of first-cousin marriage.
In three or four of these families there were more than one child so afflicted. Scott also kindly offered to place me in communication with the superintendents of a number of institutions for the deaf and dumb, and having availed myself of his kindness, I have collected the following answers.
Arthur Hopper, of the Deaf and Dumb School near Birmingham, conducted an inquiry with the utmost care. He tells me that out of pupils he has received information about the parentage of all but 9. The pupils, whose parentage is known, belonged to families; of these , there were deaf from accident or disease 37, and of 10 the cause of deafness was unknown.
Of these 10 pupils and the 66 congenitally deaf, not one was the offspring of a consanguineous marriage. Of the 37 who became deaf from disease, one was the offspring of first cousins. I am not informed whether the cases where several were deaf in a family belonged to the congenital cases, but it is almost certain to be so, and in any case I will assume as the most unfavourable assumption that it is so.
Thus, out of 62 congenitally deaf families, not one was the offspring of even a consanguineous marriage. If we were to assume the 10 other cases to be cases of congenital deafness, it would be, not one in 72 congenitally deaf families was the offspring of a consanguineous marriage.
Patterson, of the Manchester School for Deaf Mutes, kindly informs me that his pupils belong to families. Concerning 8 of these families no information could be obtained; in 67 such families the deaf-mutism results from disease; in 63 it was congenital; and only one family was the offspring of first cousins.
In one family whose parents were cousins there were 4 deaf mutes. I have thus accurate information with respect to families i. And, including the cases at Newcastle, the percentage is or 1. It is curious to notice that I deduced 2 per cent.
Thus as far as these meagre results go, no evil in the direction of deaf-mutism would appear to arise from first—cousin marriages. The failure to collect more statistics of this kind does not arise from any inability to get at the best sources of information; on the contrary, I have on all hands the kindest assurances of willingness to help me. David Buxton, of the Liverpool School, says the mode of investigation is simply impracticable; but he has sent me several pamphlets on the subject, his own excellent paper amongst the number.
Neill, who has been engaged in the tuition of the deaf and dumb for forty years, thinks the cases of offspring of cousins so afflicted are fewer than is supposed. He also gives me facts showing how strongly heritable congenital deafness is where both parents are deaf-mutes; marriages are, moreover, by no means uncommon between pupils of these institutions.
To sum up the results of the whole investigation: It seems probable that in England, among the aristocracy and gentry, about 4 per cent. Probably 3 per cent. Turning to lunatic and idiot asylums, probably between 3 and 4 per cent. Taking into account the uncertainty of my methods of finding the proportion of such marriages in the general population, the percentage of such offspring in asylums is not greater than that in the general population to such an extent as to enable one to say positively that the marriage of first cousins has any effect in the production of insanity or idiocy, although it might still be shown, by more accurate methods of research, that it is so.
With respect to deaf mutes, the proportion of offspring of first-cousin marriages is precisely the same as the proportion of such marriages for the large towns and the country, and therefore there is no evidence whatever of any ill results accruing to the offspring from the cousinship of their parents.
Professor Mantegazza states in a paper on consanguineous marriages 5 that he may conclude with tolerable safety, from his collection of cases of consanguineous marriage, that consanguinity tends to cause sterility; for he found that between 8 and 9 per cent.
It is not clear, however, how he is entitled to draw this conclusion, unless he knows what is the proportion of sterile marriages in the general population, and he admits that he has no statistics on this point.
Boudin, who wrote at an earlier date, is of the same opinion, and considers, further, that even where sterility does not afflict the consanguineous marriage itself, it is apt to affect the offspring.
I had already got a large number of marriages marked as being between first cousins, and accordingly proceeded to count the number of children arising therefrom. The marriages made within the twenty years immediately preceding the publication of those works were excluded; so that only complete families were counted. I think that the lists of the sons surviving infancy are, however, pretty complete, and any incompleteness will clearly affect the record of marriages between persons not akin as much as it does the first-cousin marriages.
The comparison to be made must, therefore, be only between the numbers of sons. I shall use the words sterile or infertile to mean the absence of children surviving infancy. The number of daughters recorded will be given, so as to show the extent of incompleteness. In this manner families, offspring of first cousins, were collected. In all but 12 of them the marriages were between children of brothers. In 11 of the it is merely stated that there was issue of the marriage, and in 8 others there is no information as to whether there was issue or not.
I found in a subsequent inquiry, by cross references to other pedigrees, that where there was no information there was nevertheless often a family; so that the absence of information is no indication of sterility, and indeed is perhaps some slight indication of fertility, because the family is omitted in order to economize space, and d. In this case, however, cross references were of no avail, because the family would be recorded in the pedigree under consideration or not at all.
The absence of information is here then a slightly greater indication of sterility than in my later inquiry, where it is no indication at all. The cases where issue was recorded may clearly be disregarded in making the comparison, since they might be matched by similar cases amongst the non-consanguineous marriages. Subtracting, then, the 11 recorded cases of issue and the 8 cases of no information, we are left with 97 families; these gave sons and daughters. It is probable that about daughters should have been recorded.
Now sons to 97 marriages is at the rate of 2. Thus the average number of sons who survive infancy, arising from a marriage of first-cousins amongst the gentry of England, is between 1. The next step was to collect the non-consanguineous marriages. In order to secure myself from bias, I opened my book by chance and counted all the marriages in the pedigree which fell under my eye.
I then did the same in another place, and so on. In this way families arising from persons not akin were collected, and found to give sons and daughters. Here, as before, the daughters are deficient, and about daughters ought probably to have been given. Now sons to marriages is at the rate of 1. Thus the average number of sons who survive infancy, arising from non-consanguineous marriages, is 1. The balance of fertility is therefore slightly on the side of the cousins, but the small difference is probably due to chance.
In order to feel greater confidence in this result, a second method of analysis was carried out. If cousin marriages tend to cause sterility, they probably tend to cause partial sterility. Now amongst the 97 cousin marriages, 14 were sterile in the sense defined , and amongst the non-consanguineous marriages 33 were sterile. Thus we have 83 fertile cousin-marriages and fertile non-consanguineous marriages; the former gave sons, the latter sons.
Thus fertile first-cousin marriages produce sons at the rate of 2. Therefore the analysis leads to a similar slight balance in favour of the fertility of the first cousins, just as did the former one. I offer the following suggestion as a possible explanation of the greater fertility of the cousins, although mere chance is the more probable cause of the difference.
Marriages between first cousins will be more apt to take place where there is a large group of persons who bear that relationship to one another. In such families fertility will be hereditary; hence it is possible that the comparison is to some extent being effected between abnormally fertile families and those in which fertility is only normal.
The next point to investigate is as to whether the offspring of first-cousin marriages are themselves affected by sterility. Concerning 29 of these no information could be obtained, and, for the reasons before assigned; these may be set aside.
Of the remaining marriages, it is recorded that 14 had issue. Subtracting these, we are left with 93 marriages, and these gave sons and daughters. It should be mentioned that some few of the marriages were recent, so that the families would be not quite complete in these cases. Now 93 marriages giving sons is at the rate of 1. Again, 16 of these marriages were sterile, so that 77 fertile marriages gave sons, that is at the rate of 2. If these two numbers, viz. The results with respect to fertility may be summed up in the following Table:.
The comparison may be best effected by means of the numbers in the last column. The comparison of the figures in the first and last columns shows, without much room for doubt, that the alleged infertility of consanguineous marriages, whether direct or indirect, cannot be substantiated. It has been stated by M.
Boudin and others that the offspring of consanguineous marriages suffer from an excessively high rate of infant mortality. I have tried to put this to the proof as follows:. Where the age of the child was mentioned, ten years was taken as the standard of youth. The 37 gave 86 sons, who survived infancy, 15 children boys and girls who died in infancy or youth, and 4 more as to whom the period of death was doubtful.
On this supposition we should have 37 fertile marriages of first cousins giving 86 sons, who survived, and between 23 and 19 boys and girls who died early. Reducing these numbers to percentages, I find that —.
One hundred fertile marriages of first cousins would give from 51 to 62 children who die young, and that for every son, offspring of first cousins, who survive youth, there are from 22 to 27 boys and girls their brothers and sisters who die early. Reducing these numbers to percentages as before, I find-. That fertile non-consanguineous marriages would give 49 children who die young, and that for every sons, offspring of fertile non-consanguineous marriages, who survive infancy, there are 22 boys and girls their brothers or sisters who die early.
The numbers to be compared are therefore 51 or 62 with 49, and 22 or 27 with These are merely two diferent ways of consulting the facts, and it appears that both methods give some evidence of a slightly lowered vitality amongst the offspring of first cousins. Thirty-seven cases form, however, far too small a total on which to base satisfactory statistics. The numbers thus collected are far scantier than those collected by others, but as far as I am aware this is the only occasion in which the method of collection has been one in which the unconscious bias of the collector could not operate.
In all these inquiries I was ignorant as to whither the figures were tending until I came to add up the totals. This last inquiry is, I fear, worth but little, but so far as it goes it tends to invalidate the alleged excessively high death-rate amongst the offspring of cousins, whilst there remains a shade of evidence that the death-rate is higher than amongst the families of non-consanguineous parents.
In my paper as read before the Statistical Society, the writings on this subject of some previous authors were reviewed. I may mention that Dr. Arthur Mitchell, of Edinburgh, conducted an extensive inquiry, and came to the conclusion that, under favourable conditions of life, the apparent ill-effects were frequently almost nil, whilst if the children were ill fed, badly housed and clothed, the evil might become very marked.
This is in striking accordance with some unpublished experiments of my father, Mr. Charles Darwin, on the in-and-in breeding of plants; for he has found that in-bred plants, when allowed enough space and good soil, frequently show little or no deterioration, whilst when placed in competition with another plant, they frequently perish or are much stunted.
It will be observed that my investigation, so far as it is worth anything, tends to invalidate this opinion; but perhaps the apparent invalidation is due to the fact, that a large majority of Englishmen live under what are on the whole very favourable circumstances. First cousins share Siblings, as well as parents and kids, share about 50 percent. Any child that results from a first cousin union is, therefore, going to have a pretty substantial portion of similar-looking genes.
And that can pose a problem. In biology, genetic diversity is all the rage. If mom and dad are genetically similar, however, both versions of a gene are likely to shut down at the same time. The real issue would arise if the next generation of kids also married their first cousins. Their offspring will have even more DNA in common—and an even greater chance for birth defects. There are plenty of historical examples of this. Charles II, the last Hapsburg king, had so many intermarried ancestors that his genes seemed more like the product of a union between siblings than the reality of uncle marrying niece.
Ultimately, marrying your first cousin carries some risk. But the odds of healthy offspring dramatically improve with each new distance of relation. Second cousins share only 6.
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