EVOLUTIONARY IMPLICATIONS OF THE DEMOGRAPHIC TRANSITION
	UNESCO Codes 2402.02, 2410.07, 5207.02 Group membership Jose A. Peña Miguel A. Alfonso-Sánchez

The biggest demographic change in the recent history of Europe is the process of urbanisation and industrialisation that followed the Industrial Revolution, traditionally referred to as the "demographic transition", which affected most European populations to a greater or lesser extent over a period of one hundred and fifty years. It was sparked off by many different factors: first of all improvements in hygiene and sanitation infrastructures including the generalised availability of running water supplies and toilets. There was also major socio-economic development, which led to considerable improvements in people's quality of life. Investment by the different states in sanitation, education and housing all increased. Vaccines were discovered and applied more and more widely, and finally there was progress in the prevention of disease, e.g. improvements in habits of cleanliness among physicians attending births, the sealing of wells in town centres and the disappearance of lazarets (places where visitors to town were quarantined during epidemics, frequently resulting in the contagion of those who arrived healthy).

As a result of all this mortality rates, especially for infant mortality, dropped markedly, so that children became much more likely to survive. The size of families increased, leading to an increase in demographic pressure that in turn led within two or three decades to decreases in birth rates.

The demographic transition can be described in three phases: first comes a pre-transitional period characterised by high birth and death rates and little or no population growth. Then comes the transitional phase, in which mortality rates drop and birth rates remain high. During this phase demographic pressure increases, so the population may increase or there may be more emigration. Finally there is the post-transitional phase, in which birth rates drop to the same low levels as mortality rates. This last phase generally takes the form of a spread in the use of birth control. The first two phases of a generalised demographic transition have already taken place in much of the world, but the third and last phase is so far observed only in modern, industrialised societies.

The demographic transition has not yet been completed in all parts of the world. It can be considered as completed in Europe as a whole, though not all countries underwent the process at the same time. In those countries which industrialised first, the demographic transition began in the early 19 th century, while in those where industrialisation came later the transition did not take place until the second half of the 20 th century.

An epidemiological transition process is usually associated with the demographic transition. Indeed, the drop in infant mortality from infectious diseases changed the mortality pattern of European populations. Historically, infectious diseases were the most frequent cause of death, but with the onset of the modernisation of European societies they have been overtaken by degenerative diseases. While in former times a large proportion of the population died within the first few years of life, there is currently no significant proportion of mortality until the end of the reproductive period. Mortality from infectious diseases must therefore have had a major influence as selective pressure on genes associated with differential susceptibility to pathogens.

Alfonso-Sanchez MA, Peña JA (2005) Effects of consanguinity on pre-reproductive mortality: Does demographic transition matter?
American Journal of Human Biology 17, 773-786

Biondi G, Vienna A, Peña García JA, Mascie-Taylor CGN (2005) Isonymy and the structure of the provençal-italian ethnic minority.
Journal of biosocial Science 37, 163-174

Alfonso-Sánchez MA, Aresti U, Peña JA and Calderón R (2005) Inbreeding levels and consanguinity structure in the Basque province of Guipúzcoa (1862-1980).
American Journal of Physical Anthropology 127, 240-252

Alfonso-Sánchez MA, Calderón R and Peña JA (2004) Opportunity for natural selection in a Basque population and its secular trend: Evolutionary implications of epidemic mortality.
Human Biology, 76: 361-381

Alfonso-Sánchez MA, Peña JA (2003) Tasas de gemelaridad e ilegitimidad en una comunidad rural del País Vasco (Lanciego: 1800-1990).
Antropo, 5, 55-62. http://www.didac.ehu.es/antropo/

Alfonso-Sánchez MA, Peña JA and Calderón R (2003) Time trends and determinants of completed family size in a rural community from the Basque area of Spain (1800-1969)
Journal of biosocial Science, 35:481-497

Peña JA, Alfonso-Sánchez MA and Calderón R (2002) Inbreeding and Demographic Transition in the Orozco Valley (Basque Country, Spain)
American Journal of Human Biology, 14:713-720

Alfonso-Sánchez MA, Panera V, Peña JA and Calderón R (2002) Demographic and health patterns in a rural community from the Basque area in Spain (1800-1990)
Journal of biosocial Science, 34:541-558

Alfonso-Sánchez MA, Peña JA, Aresti U and Calderón R (2001) An insight into recent consanguinity within the Basque area in Spain. Effects of autochthony, industrialization and demographic changes.
Annals of Human Biology, 28(5):505-521

Peña JA (2001) Estructura genética de la población del valle de Orozco (País Vasco, España) a partir de diferentes matrices de migración
Antropo, 0: 1-10

Vienna A, Peña JA, Mascie-Taylor CGN and Biondi G (2001). The ethnic minorities of Southern Italy and Sicily: Relationships through surnames.
Journal of biosocial Science, 33, 25-31.

Calderón R, Peña JA, Delgado J and Morales B (1998) Multiple kinship in two Spanish regions: New model relating multiple and simple consanguinity.
Human Biology, 70:535-561

Peña JA, Morales B and Calderón R (1997) New method for comparing levels of microdifferentiation: application to migration matrices of two populations from the Basque Country (Spain).
Human Biology, 69(3):329-44

Calderón R, Morales B, Peña JA and Delgado J (1995) Sex linked versus autosomal inbreeding coefficient in close consanguineous marriages in the Basque Country and Castille (Spain). Genetic implications.
Journal of biosocial Science, 27:379-391

Calderón R, Peña JA, Morales B and Guevara JI (1993) Inbreeding patterns in the Basque Country (Alava Province, 1831-1980).
Human Biology, 65(5):743-70

Calderon R., B. Morales, Y. Lepage, J. Peña y J. Guevara (1993) Typologies migratoires et mariages consanguins: signification demographique et genetique.
Anthropologie et Prehistoire, 104:57- 66

Morales B, JA Peña y R Calderon (1990) Consanguinity structure in a zone of Guadalajara (Spain).
Anthropologiai Kozlemenyek, 32: 39- 47

Peña JA (1988) Marital migration and distribution of surnames in Orozco valley (Basque Country).
Antropologia Portuguesa 5:283-289

@ 1997-2011, Jose A. Peña