There is a curious finding well known in some academic disciplines: girls who grow up in households without a father tend to start their periods earlier than girls whose fathers do live with them.

At first glance, this seems very surprising – what does family structure have to do with the timing of puberty? Researchers have puzzled over this question for decades, and one conclusion with widespread support is that early puberty is an evolved response to father absence. The argument runs that the lack of a father in the household is an indicator of a stressful environment.

Throughout most of human history a stressful environment would mean that the risk of death is relatively high, and when the risk of dying is high it makes sense for girls to mature early so they can have children and raise them to adulthood before the mother’s (relatively early) death. Mortality rates in human societies are now much lower than in the past, but children may still have evolved physiological mechanisms which speed up their development in stressful environments, as if they needed to get started on reproduction early.

Some people are WEIRD

But there is a big problem with this idea: almost all the data on father absence and puberty comes from WEIRD populations. WEIRD is an acronym coined by anthropologists Joe Henrich and two colleagues for Western, Educated, Industrialised, Rich and Democratic. Henrich and colleagues pointed out that the vast majority of research in psychology (>90%) comes from WEIRD populations (very often university students).

Often such research is generalised far beyond the context in which it’s gathered, and findings are assumed to hold in all other human populations. This is very problematic. The defining characteristic of our species is our behavioural flexibility. Humans have successfully spread across the entire globe because we can adapt to so many different environments. We can’t draw any firm conclusions about evolved responses then, without studying whether such responses exist in many different societies. This is certainly true when it comes to the human family.

What’s the traditional human family?

There is a widespread belief in WEIRD societies that the nuclear family is the ‘traditional’ human family. Most people do live in nuclear families in WEIRD societies, meaning that many children grow up in households with just their Mum, Dad and siblings. Outside WEIRD societies, on the other hand, families take a number of different forms, and children are often raised surrounded by a large network of relatives, including many from the extended family, such as grandparents, cousins, aunts and uncles. Marriage patterns also differ worldwide. Sometimes families involve polygyny (one man married to two or more wives), more rarely polyandry (one women married to several husbands), and societies differ in how socially acceptable divorce is, and for divorced or widowed people to remarry. So children grow up in a range of different family structures, and have variable relationships with their fathers. Some fathers are heavily involved in children’s lives; but in some societies, it may be common for children to grow up without a father constantly present in the household.

Why does this matter?

There has been a lot of research on how children’s early life experiences affects their development and health partly so that policy recommendations can help ensure children have the best start in life. Research on how father absence may be associated with early puberty – which is sometimes linked to poorer health and social outcomes in adolescence and later life – is therefore useful to some WEIRD policy-makers, who have argued that the nuclear family is the best environment to raise children, and enacted policies which encourage marriage and the formation of such families. Such policies risk ignoring the evidence from many populations that children can thrive in a range of different family structures, and may actually benefit from exposure to many different family members. This is particularly important in large and socioeconomically unequal populations such as the US, because WEIRD data are often from relatively wealthy and highly educated sections of Western populations, meaning that results may not generalise to marginalised populations even within the same society. For policies which affect the family, therefore, we need a solid evidence base on which to understand associations between family structure and child outcomes.

What did we do?

My colleagues, Paula Sheppard and David Coall, and I decided to thoroughly search the literature to find out what the evidence really says about the association between father absence and puberty. We included in our investigation a search for studies which had tested for this association outside WEIRD populations, and a look at whether boys appeared to be affected by father absence. It seems plausible that, if father absence causes a physiological response in girls then it should also do something similar for boys, but most research has focused on the impact of father absence on girls’ puberty. This is probably because there is an easy-to-remember measure of puberty in girls – age at first period (menarche) – whereas for boys, collecting data on puberty involves asking questions about events which may be more difficult to remember or are more sensitive, such as the age at voice-breaking or other physical changes, such as the growth of body hair.

So what did we find?

We found about 80 papers which had data on the association between father absence and the timing of puberty, and counted up the number of papers which found that father absence was associated with early puberty; the number which found associations with later puberty; and the number that found no association. For WEIRD girls, a link between father absence and earlier puberty was found in a majority of studies - about 60% - but not all (see Figure below). But the picture was quite different when non-WEIRD societies, or boys, were studied. Outside WEIRD societies, father absence was sometimes associated with delayed puberty, particularly for boys.

Is there a universal, causal effect of father absence on age at puberty?

So what does this complicated picture mean? There are few studies which have attempted to collect data on the proposed physiological stress mechanisms which underlie associations between father absence and puberty, so that it’s hard to know whether these associations are the result of a direct effect of father absence causing earlier puberty. But some researchers have shown, in WEIRD societies, that earlier puberty is more closely associated with markers of family stress such as arguments within the household than with father absence itself, and that children with close relationships with fathers, even if they don’t live in the household, may not experience early puberty. This supports the idea that stress in childhood may cause early puberty, though it may not be father absence itself that affects children, but other stressful experiences which may be associated with father absence in WEIRD societies – for example, divorce may be relatively stressful in societies where the nuclear family is considered the norm.

The fact that father absence tends not to be very often linked to earlier puberty outside of WEIRD populations could have several explanations. One is that father absence doesn’t cause stress to children in all societies. Another is that an important role fathers often play is to provide food for children, so that where fathers are absent, children may be relatively poorly nourished. This may explain why in some societies father absence is associated with delayed puberty: growth and development takes energy, and poorly nourished children may experience relatively late puberty. If this explanation is true, though, it does raise questions about the evolved response to stress which WEIRD girls are proposed to experience in stressful family environments: throughout most of human history, food supply was relatively restricted, meaning that there may have been little opportunity for accelerated development to evolve in response to early stress.

The bottom line is…

We don’t yet have enough information to really know whether associations between father absence and either early or late puberty reflect truly causal relationships. But this literature review does show that any relationships between father absence and the timing of puberty are likely to depend on the role of fathers within the family, as well as other factors which influence puberty but vary between populations, such as food availability.

The most important take-home message is that it is impossible to draw conclusions which apply universally to all individuals in all populations without having good data from outside the very narrow slice of humanity which is Western, Educated, Industrialised, Rich and Democratic.

Read the full article here:

For more information on the authors, please see the following:

Paula Sheppard:

David Coall:

Rebecca Sear: