There are three questions which come up in relation to the growth of religious movements, particularly the Christian faith. How would you answer each of these?

a. Why is Islam growing in the UK and in the world at the moment?

b. What was the primary reason for the growth of the early church?

c. Why in the West do conservative churches generally resist the decline that affects more liberal ones?

Now these are big questions, and the answers are bound to be complex. But generally in answer to (a) most people will reach for an explanation around the rise of fundamentalism and a global rejection of Western liberal values. In answer to (b) many will think about the cultural and religious distinctiveness of the early Christian movement, and its appeal in relation to the cruelty and fatalism of much pagan religion. And in answer to (c) many will reach for ideas of commitment and discipleship which resist the corrosion of modern individualist and consumerist culture.

But there is a good case to be made that all three have the same explanation: childbirth.

Let’s consider Islam. Although the Muslim population is set to increase because of immigration, a much more powerful longer-term factor is differential rates of childbirth compared with the indigenous UK population.

The Muslim population of the UK is set to triple in 30 years, according to projections from the Pew Research Centre. Under the model which assumes median migration levels, the number of Muslims in the country would rise from 4.1m in 2016 to 13m in 2050. It said the research followed a “record influx of asylum seekers fleeing conflicts in Syria and other predominantly Muslim countries”. The UK also has one of the largest gaps in fertility rates between Muslims and non-Muslims, with Muslim women having an average of 2.9 children compared to the 1.8 had by non-Muslims. This means that even if migration were to stop completely, the group’s population share would rise by more than 3 per cent in the UK, as well as in France, Italy, and Belgium.

In contrast to growth through migration and birthrates, only 2.9% of UK Muslims consider themselves to be ‘converts’. The same is true globally; the primary reason why Islam is growing around the world is that predominantly Muslim countries have a lower average age and higher fertility rate than non-Muslim countries.

In 2006, countries with a Muslim majority had an average population growth rate of 1.8% per year (when weighted by percentage Muslim and population size). This compares with a world population growth rate of 1.1% per year. As of 2011, it was predicted that the world’s Muslim population will grow twice as fast as non-Muslims over the next 20 years. By 2030, Muslims will make up more than a quarter of the global population.

Secondly, what about the early Christian movement? Rodney Stark, in his The Rise of Christianity, offers some fascinating analysis of what we can discern about the way in which growth happened, including the nature of their message, the integrity communicated by martyrdom, and the difference that care and compassion made when disaster struck, especially in the form of plagues. But childbirth is a significant contributor. Tim Chester, in his critical review, summarises:

Chapters four and five are more compelling. But what is striking about these chapters is they offer more historical evidence, both from Christian and pagan sources. Here Stark argues that Christianity grew because of its response to epidemics (more of this below) and because it gave women higher status and produced higher fertility rates. Men outnumbered women in the Roman empire, largely due to female infanticide and mortality during abortions. In the church, however, women outnumbered men because Christians rejected infanticide and abortion, and because more women converted. (Stark provides plenty of compelling historical evidence of these claims.) As a result, fertility rates among Christians were higher, contributing to an increase in the proportion of Christians in empire.

It is interesting to note here that ‘women outnumbering men’ has often been seen as a challenge to the church, with concerns about potential feminisation of church culture and the possible implications of that. But as Stark points out, it is women who have children (!), and if those children grow up in the faith, then that will have a significant impact on intergenerational church growth.

Thirdly, why have conservative churches generally been better at resisting decline than liberal churches in the West, including the UK? I would want to argue on several fronts: those who proclaim a faith that is more distinctive from surrounding culture actually have a message which might draw people; there is strength in drawing people together with a shared belief; consistency provides a welcome refuge from the unending changes and challenges of the world around; and the message might actually be true! Deep down, people are drawn to what they perceive is true. So I was rather taken aback to read Steve Bruce’s argument about the power of social-scientific research in relation to religious belief, to promote his book summarising a lifetime of such work Researching Religion: why we need social science. He begins with challenging some fondly-held beliefs:

Consider four common assertions about religion in Britain. People become more religious as they get older because their approach to death makes them mindful of their souls.

Wars and other social crises provoke religious revivals.

Religion is not declining; it is just changing its shape. Traditional Christian churches may be in trouble but Pentecostal, charismatic and independent evangelical churches are recruiting the religiously indifferent and the New Age spirituality milieu is attracting large numbers of seekers.

The British have stopped belonging to churches but they are still believing. What has declined is not religious sentiment but the willingness of people to associate. Each of these assertions sounds plausible and might well be true. We could draw on our own experience, on biographies, or on small-scale ethnographic studies to demonstrate their validity. They are actually false. And we can prove that with large-scale statistical data.

In amongst the assumptions he challenges are the ones about conservative churches resisting decline.

I began my career as an ethnographer, scornful of conventional social science and rude about statistics. I only gradually converted as I repeatedly made mistakes. To explain just one, I and many others spent a good part of the 1980s arguing about why conservative churches were growing while liberal ones were declining. We debated just which features of ‘strong’ religion explained its appeal. Turned out we were wasting our time. Demographers demonstrated that the most significant difference between conservative and liberal Protestantism was not their relative appeal to the unGodly but the typical family size of existing adherents. Conservatives had more children. Even if both sides had been equally good at recruiting their own children, the liberals would have declined faster. An ethnographer who studied a conservative and a liberal church might just have spotted that (though none did!) but it took the statistical analysis of large-scale data sets to show we were not just barking up the wrong tree but barking in the wrong forest.

That is not to suggest that the other factors are completely unimportant in contributing to church growth (after all, the big ‘if’ here is ‘if both sides had been equally good at recruiting their own children’ and there are all sorts of factors at play here), but that rates of childbirth and family size are significant—and usually feature nowhere in the discussion.

So it appears that, from the contemporary growth of Islam, from the historical growth of the early church, and from recent experience in Western culture, one of the best long-term strategies for church growth is to encourage Christians to marry and have children, and have more than average.

There are a number of serious objections to adopting this as a church growth strategy.

The feminist objection argues that focussing on childbirth affects women more than men, and taking this approach will push us back into a patriarchal culture in which inequality between the sexes grows again. Taking time off to have children is in fact the biggest factor in the so-called ‘gender pay gap’—but what if women do actually want to have children? In what way is it ‘feminist’ to deny them this—or create a culture in which they have the double pressure of parenting and working, rather than being rewarded for taking time off for the family? And why do we assume that fathers should not also be involved? We had three children, and my wife continued as a partner in her GP medical practice because I worked part-time from home and her parents also provided support.

The pastoral objection is that many churches already focus too much on the nuclear family, to the point of appearing to proclaim salvation by childbirth and parenting, in which the single, the infertile, and the divorced are hurt and marginalised. I think that is a serious danger, and needs to be addressed at every point.

The environmental objection is that there are already too many people in the world, and we are destroying the planet by exhausting its resources. If anything we should be having fewer children, not more. But that simple claim omits four important facts. First, as the late Hans Rosling graphically illustrated, population growth is primarily caused at present by the bulge in young people, and this settles down as populations escape poverty, so that the global population is already set to level off. Secondly, Western countries already face a major challenge in their declining fertility and declining indigenous population, which will lead to the demographic ‘time bomb’ of an elderly population with insufficient resources in the working population to support them. Why would we want to contribute to that problem? Thirdly, the primary issue in population is the differential rates of population growth around the world. And finally, if we all cut our eating of meat, and were more vegetarian, many of the resource challenges would be dealt with.

Fourthly, there is the theological objection. Where there is death, there needs to be marriage and procreation, since there is no other way to preserve one’s name for posterity. This is the theological and anthropological assumption behind the first commandment that we find in the Bible:

So God created human beings in his own image, in the image of God he created them; male and female he created them. God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground.” (Gen 1.27–28)

But for Christian, we are living under the (re)new(ed) covenant in Jesus. We worship a single saviour, and the apostle who wrote much of the New Testament was also single. Our new task is not simply to procreate, but to evangelise; our new family is not simply those we are related to by blood, but those we are related to by discipleship; growth comes less by having physically children, but by having spiritual children, which explains some of the extraordinary language in the New Testament.

He replied to him, “Who is my mother, and who are my brothers?” Pointing to his disciples, he said, “Here are my mother and my brothers. For whoever does the will of my Father in heaven is my brother and sister and mother.” (Matt 12.48–50) My dear children, for whom I am again in the pains of childbirth until Christ is formed in you… (Gal 4.19) To Timothy my true son in the faith: Grace, mercy and peace from God the Father and Christ Jesus our Lord. (1 Tim 1.2)

But the reality is that we are not simply inhabitants of the age to come; we are also at the same time inhabitants of this age. So, although we live under the dynamics of the kingdom of God, we also continue to live under the dynamics of the created world. We are not yet completely free from the obligations set out in the creation narrative. Only when there is no more death will there be no more marriage and procreation.

So what would it look like to adopt this church growth strategy?

First, it would require explicitly countering our cultural narrative that we find fulfilment in success, in career development, and in the acquisition of stuff. As Will Jones points out, there are all sorts of cultural reasons behind the decline in family and childbirth in Western culture. But for me, the main ones are around the fact that having children is expensive and inconvenient if your goal in life is material prosperity.

Secondly, it would need positive teaching about the value and reward inherent in Christian teaching about family and sexuality. This would need to include teaching on the importance of parenting for both men and women.

Thirdly, it would need an essential both/and approach in relation to questions of family, singleness, and the healing of broken relationships. We live in the overlap of the ages, so family and parenting is important and to be valued, as is singleness. It is worth noting that having families has in the past been highly valued within Christian discipleship, but so has the example of singleness modelled in mission and leadership (think John Stott).

Fourthly, we need to provide for non-Christian spouses of Christians, and in particular for non-Christian men of Christian women in a positive and open way.

Fifthly, it would need to include a strategy of reaching young people in their teens and twenties, perhaps through culture change in the church effected by church planting. I find it curious to talk about ‘attracting children to church’, when in fact it is not children who bring themselves. Our churches will be full of children if and when there are young people in our congregations who get married and have families. That is how it has mostly happened in the past.

Sixthly, we need to take seriously the challenge of parenting through adoption, as exemplified by the remarkable work of Krish Kandiah and Home for Good (as well as others).

Seventhly, we need to provide patterns of discipleship for children which are integrated with, rather than disconnected from, family life. This is the best way to encourage children to grow in their faith.

However it happens, this doesn’t appear to be optional if we want to see the church grow again. There is even a name for it in the church growth literature: biological growth. The evidence strongly suggests that the future belongs to whoever takes this seriously.

You might want to raise further objections, or suggest other things that are needed. Fire away in the comments!

Follow me on Twitter @psephizo. Like my page on Facebook.

Much of my work is done on a freelance basis. If you have valued this post, would you consider donating £1.20 a month to support the production of this blog?