The changes suggested by functionalism seem mistaken, but it's impossible for institutions to remain unaffected by time. Humans are creative and adaptable and institutions are their creations; nobody keeps on tolerating conditions that they are capable of changing and advances in knowledge will further hasten changes in social organisation and belief.
In "The Family in Question" (1985), Gittings suggests some historical changes in families. The first of these is mortality.
Life expectancy has increased dramatically. In England in the late 17th century, the average life expectancy was 32 years. (Increased life expectancy has implications for life-long marriage/partnership - consider what they are). This short life expectancy had clear repercussions.
First, if parents wanted children to survive they needed to produce a relatively large number of children (some would die).
Second, marriages and families were frequently broken by death. Widowhood, like orphanhood, was a common experience. So, the belief that families in the past were more stable and solidaristic than today cannot be borne out.
High mortality meant it was rare for children to know their grandparents for long, if at all. Given this, the extended family could never have been widespread, or long-lived. (Beware the 'rose tinted' view of the 'golden past').
In pre-industrial society, there was always a high fertility rate. Until the late 19th century, society was a very young society. In the 20th century, Britain has become an increasingly old society. Age has an important effect on family resources. The elderly require time and attention but cannot contribute much (materially!) in return.
Additionally, it is women who are seen as responsible for caring for many of the elderly.
The amount of time spent on child-rearing is also increasing. Although less time is spent actually having children, more time is spent rearing them.
Apart from the very wealthy, everybody in medieval and early modern society was expected to work, as economic survival depended on it. If working for wages, a family needed more than one to survive; there was no such thing as a 'family wage'.
Because the wages of women were low, most women needed (materially) to reside with a man. Industrialization increased the dependency of women on marriage.
Alongside this, the trade unions developed the concept of the family wage with the husband/father as sole breadwinner, which was a powerful factor in the development of modern notions of masculinity. This development coincided with the new middle class ideology of women and children as dependents of the husband/father.
This bourgeois ideology developed between 1780-1850. It was not just a family ideology, but a gender ideology - a careful and deliberate attempt to reorganize relations between the sexes, according to middle class values.
Some things are clear:
The functionalist account is untenable - there is no basis in the available data for their argument.
Diversity seems the best description of both historical and contemporary family arrangements.
There have been changes to family life because of societal changes, such as advances in sanitation and communications leading to changes such as increasing life expectancy, the lowering of infant mortality rates and the aging of the population.
Source: D. Gittins 'The Family in Question' (1985)