An approach to the extreme singularity of the blood characteristics of the Basque population requires studying the following aspects: the authors who have investigated Basque blood, the different blood s investigated, the results obtained and the consequences reached. The list of researchers is endless: Boyd and Irizar (1937), Etcheberri (1945), Mourant and Chalmer (1948), Ruffie (1958), Goti (1966), Valls (1969), Levine (1974), Iturrioz (1979).
Among the blood s the most important achievements correspond to ABO, ABH-secreting, Lewis, Rh, MNSS, P. Kell, Duffy, a group of enzymes called haptoglobins and transferrins and other genetic markers. It should be noted that given the conditions imposed by the determination of polymorphic s (Rh, MNSS), the number of individuals phenotyped in certain studies is low. Sometimes the sample is completed with a cosmopolitan population, embassy staff and also with Basques who emigrated to America; all of this casts doubt on the relevance of the groups investigated. The blood groups of Basques, according to the results obtained, lead us, according to E. Valls, to paradoxical conclusions:
"desde un punto de vista morfológico, parece que, según lo investigado, son un tipo humano local que tiene características mediterráneas y alpinas y, a primera vista, en la frecuencia de estos caracteres se encuentran diferencias entre los del norte y los del sur. Las divisiones de grupos sanguíneos realizadas mediante los sistemas llamados ABO y Rh (por lo menos las de éstos) distinguen a la población vasca de la del resto de Europa Occidental. Desde un punto de vista serológico no es, pues, demasiado inapropiado hablar, como ya lo hizo Boyd, de una raza vasca. En la división actual de los grupos sanguíneos es importante la influencia de la presión selectiva y la deriva genética. Es posible que el aislamiento geográfico de la población vasca haya hecho surgir un tipo de demografía dependiente de procesos endogámicos y que, como consecuencia de esta endogamia, haya habido un cambio profundo en la frecuencia de alelos de los grupos sanguíneos mencionados. Esto explicaría el desacuerdo entre los hechos serológicos y los antropométricos y, al mismo tiempo, el desacuerdo entre las clasificaciones realizadas según unos u otros caracteres".
In summary, we would add that the antiquity of the population as attested by prehistoric traces, the geographical isolation increased by the barriers imposed by a language without kinship ties and the consequent influence of the variability factors in this special biological community, to all of which must be added the special ethnicity and culture, have resulted in the production of the unique haemotypes of this particular collectivity.
As far as the MNSS s are concerned, the Basques have not produced results that are out of line with the variability found in Caucasians. As suggested by research done by Leviene (1974) on the Northern Basques, fundamental disagreements may appear in some gene complexes.
With regard to the P. Kell, Lewis, and ABH-secreting s, no significant difference has been found that is equivalent to that found in the MN case. The Duffy , on the other hand, s a high frequency of FyB + Fy alleles in the Basque population. This has been demonstrated by R. Iturrioz (1979). This is a significantly clear difference with respect to the European population but, given that there are also differences the populations of the different Basque regions, it should be mentioned that, according to some blood group s, the population is not homogeneous. This is the case in the Encartaciones, in the Mundaka estuary (Busturia) and Arratia with respect to the ABO and MNSS s. The peculiar situation of the eastern region of Bizkaia (Derio-Mungia) must also be pointed out, as it is different from the rest of the regions according to the ABO . As far as Rh negative is concerned, the very high values of the CDE and CDE genetic complexes (haplotype) and the appearance of the CDE genetic complex, which is so rare in the other populations, provide additional data on the haematological characteristics of the Basque population. According to this , the classification of racial variability ranges from Mongoloids and Amerindians who do not have Rh negative (q=O) to the highest frequency (q=0.6), which is found in the Basque population. It seems that the haemolytic disease that occurs in the neonate due to fetomaternal Rh incompatibility has been, for most of the evolution of Homo sapiens, a selection mechanism. However, although 10% of children would be expected to suffer from the disease according to the above-mentioned proportions, the proportion is much lower, as has been seen experimentally in the Basque Country and other populations; in fact, one sick child is born in every one hundred and fifty. And the incompatibility of the ABO group, which is the protection against Rh incompatibility, is much smaller still, which is why this disease only really affects 5% of the expected infant population.
The main reason for this lies in the following: fetal red blood cells that are incompatible with the mother are destroyed by the mother's anti-A or anti-B antibodies, so that this rapid destruction does not allow time for the red blood cells to stimulate the maternal immune that would produce anti-Rh-positive red blood cells. On the other hand, it seems that a balance is achieved in Rh-negative mothers by compensating for the loss of heterozygous offspring with increased fertility. As the percentage of Rh-negatives is 53 % in the Basque population, it is the only known population that has surpassed the 50 % mark. Mourant (1974) and Cavalli-Sforza (197l) have proposed the following interpretation of the hematic singularity of the Basque population:
"entre el este y el oeste de Europa hay un gradiente decreciente del grupo B en el sistema Duffy, ya que la población vasca, que presenta la frecuencia más baja de este alelo, representa el extremo occidental del continente; y, emparentada con los pueblos antiguos del extremo europeo, ha conservado una tipología sanguínea específica que no se explica mediante los sistemas de los grupos sanguíneos de ningún otro pueblo europeo".
Similarly, in the HLA blood leukocyte , the Al and B8 alleles of some antigens have a tendency to coalesce at the population level, resulting in what is known as linkage disequilibrium. When populations unify or interbreed, there is often an imbalance Al and B8, as was the case, for example, in the Near East as a result of the great Indo-European migrations. This imbalance is nil or almost nil in the Basque Country and Sardinia, which means that these migrations have not influenced the Basque or Sardinian population. This being so, M. Marquer himself has admitted that:
"there is no doubt that the serological formula of the Basque population is very old... on the contrary, the morphological characters that have modelled the Basque type with the appearance it has now and, especially, the brachycephalisation of the northern Basques, presumably have a more recent origin".
In the words of Vallois (1951):
"el por qué del desacuerdo entre los resultados de la serología y la morfología podría encontrarse en el origen independiente de cada uno de ellos y, del mismo modo, en el desplazamiento a lo largo del tiempo de los caracteres que les corresponden".
From the point of view of breeds, the answer to this last statement could be that, given the variability of the morphological nature, the significance of the genetic nature is more important. And even if it is not very obvious that morphological variability depends more on genotype than on environmental influence, it is increasingly necessary to admit that, in many cases, the reason for morphological variability lies in genetic differences. As far as plasma proteins are concerned, the haptoglobins of the Basque population, being differentiating markers that can be used in the same racial group, have given statistically significant differences with all the European Caucasian populations, and the same has happened with D esterase. With respect to these markers, and differing from the Basque population, the Castilian population fits in well with the Caucasian population of Europe. However, the population of Burgos s similarities and differences with the Basque population and with other Castilian populations, and can therefore be considered as a transition zone. The high level of reliability achieved by Marian Martínez de Pancorbo in the electrophoretic development of haptoglobin activity bands using a migration time of almost fifteen hours has led to results that are different from those obtained by Allison (1959) and Planas (1963). In addition to this, as the Basque sample has been chosen more carefully, the claim that the Basque population differs from the rest of the European population with respect to haptoglobin is now more well-founded. In addition to the serological traits, we will add two biochemical modalities: earwax and taste sensitivity to the bitter substance called PTC (Phenylthiocarbamide). The anthropological analysis carried out by R. Calderón (1977) on the variability of earwax in the Spanish population has proved that, out of the 1,153 people investigated, the highest frequency of the so-called dry earwax is found in the Basque group, with significant differences in the distribution of the two forms of earwax in the Basque and Andalusian populations. A unique physiological characteristic of the Basque population is the great taste sensitivity to the substance phenylthiocarbamide, which is very interesting in the genetics of human populations. Due to the low percentage of "non-tasters", the Basque population is not only different from the peninsular population, but also from the European population. Research carried out by R. Carballo has confirmed the results of Basabe (1964) and the existence of a gradient that grows from Bizkaia to the Roncal Valley in Nafarroa. Earwax and the so-called PTC are two more characteristics that place the Basques in a special typological situation.