Why give to good causes? In different times and different cultures there have been many answers to that simple question, ranging from religious obligation to personal vanity and the concern that a fortune amassed in one generation might otherwise be frittered away by feckless heirs in the next. But what matters, arguably, is not so much the ‘why?’ of philanthropy but the ‘how much?’ and ‘how widely spread?’: in many parts of the world, health care, education and the arts are largely or wholly dependent upon it.

Arguably, too, what matters is the spirit behind the giving. Ancient Greeks used the adjective philanthropon as a way of describing ‘someone who is gentle and kind towards others’. ‘Charity’, another key word here, is synonymous with ‘love’ in a famous passage in the Bible. The banker John Studzinski, in one of the interviews with modern-day philanthropists that separate the chapters of this book, opines, ‘In the end, it’s about human dignity.’

But is it? In this huge study, the fruit of five years’ research, Paul Vallely traces the history of giving from ‘ancient Greeks to the modern geeks’ in order to examine the dichotomy between two very distinct schools. The first is ‘reciprocal philanthropy’ that is driven by the heart, creates emotional ties between givers and recipients and by its nature involves widespread dispersal of resources across many causes. The second is ‘effective altruism’, which is targeted, large-scale philanthropy designed to harness market forces in an attack on the world’s most life-threatening problems.

Witnesses for the reciprocal school range from Aristotle to the Quaker chocolate makers George Cadbury and Joseph Rowntree, pioneers of model villages and staff welfare. Its spokesman today is Pope Francis (of whom Vallely is a biographer), who has said that when giving to a beggar, ‘it is not a good thing just to throw a few coins … gesture is important … looking them in the eyes and touching their hands.’

The opposing party would call that sentimentality and demand to know what useful outcome the throwing of coins actually achieves. Their patron saint is the ruthless 19th-century Scottish-American steel baron turned philanthropist Andrew Carnegie; today they are represented by Bill and Melinda Gates and Facebook founder Mark Zuckerberg and his wife, Priscilla Chan. Their multi-billion ‘philanthrocapitalism’ is about efficiency rather than love: it involves redeploying methods that brought success in business and finding innovative technical solutions that focus resources where they have the greatest impact. In practice, the Gates Foundation has done great work in all but eliminating polio and greatly reducing malaria in Africa. In personal terms, adherents argue that it’s better – because it will save more lives – to make a career as a banker in order to get rich and be in a position to give large sums to efficient projects than to follow the heart by becoming an aid worker in a charity that’s not run like a business.

Clearly there are many aspects to this argument. Of course some heart-driven giving is self-indulgent, motivated by a desire for recognition, or misdirected. Of course appeals for faraway medical emergencies should take priority over country house opera companies closer to home. The impact philanthrocapitalists can make on famine, sickness, literacy and crop fertility in the poorest parts of the world is undoubtedly considerable. But then there’s the argument that the rich should simply pay more tax and allow resources to be distributed as voters decide, rather than on the whims of billionaires.

All these issues are examined by Vallely, who offers a two-thousand-year perspective that takes account of changes in the roles of religion and government as well as in the scale and concentration of wealth. Philanthropy is as awesome in breadth as it is meticulous in detail, from its analysis of the impact of the Black Death – which led to ‘the death of feudalism and the rise of the beggar’ – to its examination of the opaque tax structures favoured by the likes of Zuckerberg as vehicles for their philanthropic ventures. And the sheer bulk of text is helpfully broken up with interviews that provide a great deal of illumination about different approaches to giving.

Here is gentle Jonathan Ruffer, a financier with a Christian conscience who has sunk a nine-digit fortune into restoring the self-esteem of one depressed northern English town, Bishop Auckland, observing that ‘it’s very liberating to give money away … [people] don’t realize how much fun it is.’ Here is the cerebral David Sainsbury of the grocery dynasty, the first Briton to have given (over a period of five decades) more than £1 billion to charity, talking about why philanthropy is better than government at innovation, risk-taking and social research. And here is Bob Geldof, whose Live Aid initiative raised £150 million for famine relief and development in Africa, in large part thanks to his in-your-face way of asking for money and confronting political leaders: ‘I can say what I like, I don’t give a fuck what anyone else thinks.’

In his eloquent conclusion, Vallely makes the case for the reciprocal over the effective. We are where we are today because governments are strapped for cash, churches are impotent and capitalism has created fortunes so large that their owners cannot possibly spend them on themselves. But still philanthropy is best when it forms a thousand points of light: individuals supporting a multiplicity of causes through personal choices and connections and donations large and small – not as a substitute for the state but as a complement to it. The alternative, of the mega-wealthy directing resources at big problems because they think they know best how to solve them, also helps the world – and only those who despise wealth itself will argue against it. But Paul Vallely is right to call it an evolution of philanthropy that lacks a human face.