lines of thought which are usually taken from into analysing the decline of infant mortality rates, the first line of thought comes from social historians, who ascribe the decline of infant mortality to social phenomenons of the time such as the need for a healthy population for the sake of the nation's fighting capabilities and political issues surrounding women. The second line of thought comes from demographers themselves which more or less ascribe the decline of infant mortality itself more to the general decline of mortality altogether in the society than any particular reason why. Physical unfitness during the Boer War came into national prominence as many recruits came back to be too medically unfit for service. With this, In 1904, the Report of the Inter-Departmental Committee on Physical Deterioration was published which listed large amounts of details of the failings of the British population, and for that matter government, in sustaining a healthy population. The current rate of infant mortality in the United Kingdom is roughly around 3.82 deaths per 1,000 live births. Age structure Interlinked with fertility and mortality, The age structure of the United Kingdom has varied with how rates of fertility and mortality have changed throughout the country's history. Due to the transition to an industrialised society, the United Kingdom has also undergone a 'demographic transition': that is to say, that it has gone from a high birth rate, high mortality rate society to a low birth rate, low mortality rate society over the space of two centuries. Before the 18th century, the United Kingdom retained an age structure universal to societies in the first stage of the transition theory, with high fertility rates and high mortality rates, in the late 18th century, the Industrial Revolution began, kickstarting the country's transition into the second phase: mortality rates declined but birth rates stayed at the same level; by 1870, the country had begun to transition into the third phase: the birth rate began to decline from around near 5 children per woman to below replacement level in the 1930s. The fourth phase of the transition began in the 1960s, when the fertility rate rose, and peaked during the middle of the decade, and then collapsed by 1973 to a below replacement level rate. Since then, the rate has not risen to an above replacement level fertility rate; this has resulted in a population which is currently ageing: