BOOKS & ARTS COMMENT

considered. It matters whether power refers to electricity or biomass. And it matters whether land is used exclusively or only partly for energy. Smil raises this issue but does not address it systemi- The cradle of cally. He could have used the concept of exergy (energy’s ability to perform use- ful work) to differentiate between high- humankind revisited quality energy (such as electricity, which is versatile) and low-quality energy (such Michael Cherry catches up with new developments and as straw, which demands costly conver- old dilemmas at South ’s hominin- hotspot. sions to become usable beyond burn- ing). However, his comparisons look only at power densities, irrespective of reach the sediba was quality. Smil sketches out a valuable tax- after half an hour’s drive discovered at Malapa Cave onomy of energy-related land uses along from , in . two dimensions. The first is exclusivity: Ithrough the the site of a power plant, for instance, is Highveld of South Africa. view excavations, once unusable for agriculture; right-of-way This open, grassy space they resume at the site. land underneath transmission lines is scattered with trees (Digging has been on not. The second is longevity of use: a is a World Heritage hold since 2009, when the nuclear-waste repository will be in Site, riddled with remains of four A. sediba

NATURAL HISTORY MUSEUM LONDON/SPL HISTORY NATURAL place for centuries, whereas an annual limestone caves individuals were removed.) crop such as maize (corn) for conversion and hominin . The Beetle protects the delicate lime- to ethanol can be grown in rotation. Yet A substantial chunk of the evidence that stone system from rain, and lets wild animals Smil does not use Africa is the wellspring of humanity was dis- move freely below. Standing on eight clavi- “Cities will this taxonomy, and covered here; and with anthropologist Lee cle-like supports, it has a fabric roof that col- require vast as a result some- Berger of the University of lects rainwater and channels it to a sanitation renewable- times compares (Wits) in Johannesburg set to unearth more system. Visitors will watch excavations from energy ‘apples and oranges’. at the Malapa and sites, the a raised circular walkway. A pulley below Unlike in some Cradle still rocks. the platform is attached to a hoist capable of hinterlands.” of Smil’s other As a heritage site in a developing coun- bearing a tonne of rock. books, the produc- try, the area is a focus for national pride. But But there are questions over how ‘public’ tion quality of Power Density is regret- developments there are spurring questions the Beetle actually is. Costing half a million tably low. I prefer readable graphics over which part of the nation they serve. US dollars — paid for largely through the accompanied consistently by source Palaeontologists will rejoice over the National Research Foundation (using taxpay- and data referencing. In this book, many launch, on 21 July, of a state-of-the-art vault ers’ money), as well as Wits and the Gauteng graph labels are hardly legible, and fig- to house star local finds, an adjunct to Wits’s provincial government — the site is in a pri- ures with references are the exception. Centre of Excellence for Palaeosciences. The vate game reserve and the tourists, when they Sometimes sources are mentioned in vault will allow specimens to be compared come, will probably be rich. The Maropeng the text but not in the caption; at others, with other finds, both hominin and non- centre demonstrates this. Built at a cost of they are not even in the text. Graphs plot hominin, from around Africa. These include US$29 million, it charges $13 for admission data on population and energy use, but the skull (Australopithecus africanus), (around half that for students), which prices statistical data sources are not specified dated to between 2 million and 3 million out many in a country where one-fifth of the or referenced. years ago, which was discovered north of people still live on $28 a month. That could Power Density’s detailed examina- Kimberley in 1924; specimens of Austra- be reflected in Maropeng’s visitor numbers. tion of the spatial constraints of energy lopithecus sediba discovered at Malapa, Planned to accommodate 1 million visitors a options adds to Smil’s earlier, pioneering including a remarkably complete skeleton year, it receives between 230,000 and 250,000 treatment of the subject, making it useful called MH1, as well as casts of East African and runs at an annual loss, picked up by the for energy specialists interested in explor- discoveries such as Lucy (Australopithecus provincial government. Kruger National ing a massive ramp-up of renewables. But afarensis) and the type specimen of Park, by contrast, charges different rates for its technical nature and language make it habilis, found by anthropologists Mary and South Africans and foreign tourists, and rather inaccessible to a wider audience. Louis Leakey. The vault’s laboratory has a receives 1.4 million visitors annually. And its failure to explain fundamental micro-CT scanner and 3D printing facilities. Remarkable fossils continue to emerge in concepts such as the difference between But it is strictly for researchers’ use. the Cradle, and it presents no less remark- power and energy, and to provide ade- What is there for the public? The able opportunities for palaeo­tourism. But a quate data and source referencing, make Maropeng visitor centre opened a dec- way must be found to make the specimens it unsuitable as a textbook. ■ ade ago as an interpretation centre for the widely accessible. In situ interpretation of Caves, site of the discovery australopithecine remains should present Arnulf Grubler is at the International of the ‘Mrs Ples’ fossil (Australopithecus a uniquely uplifting experience for all, rich Institute for Applied Systems Analysis africanus) in 1947 and, 50 years later, Little and poor. ■ in Laxenburg, Austria, and the School Foot, the most complete early-hominin skel- of Forestry and Environmental Studies eton known, which is as-yet undescribed. Michael Cherry is in the Department at Yale University in New Haven, And late last year, a light, moveable, steel of Botany and Zoology at Stellenbosch Connecticut. structure known as the Beetle was placed University in South Africa. e-mail: [email protected] over the Malapa site to let the paying public e-mail: [email protected]

2 JULY 2015 | VOL 523 | NATURE | 33 © 2015 Macmillan Publishers Limited. All rights reserved