Biologists classify organisms into species. Animals are said to belong to the same species if they tend to mate with each other, giving birth to fertile offspring. Horses and donkeys have a recent common ancestor and share many physical traits. But they show little sexual interest in one another. They will mate if induced to do so – but their offspring, called mules, are sterile. Mutations in donkey DNA can therefore never cross over to horses, or vice versa. The two types of animals are consequently considered two distinct species, moving along separate evolutionary paths. By contrast, a bulldog and a spaniel may look very different, but they are members of the same species, sharing the same DNA pool. They will happily mate and their puppies will grow up to pair off with other dogs and produce more puppies.
Species that evolved from a common ancestor are bunched together under the heading ‘genus’ (plural genera). Lions, tigers, leopards and jaguars are different species within the genus Panthera. Biologists label organisms with a two-part Latin name, genus followed by species. Lions, for example, are called Panthera leo, the species leo of the genus Panthera. Presumably, everyone reading this book is a Homo sapiens – the species sapiens (wise) of the genus Homo (man).
Genera in their turn are grouped into families, such as the cats (lions, cheetahs, house cats), the dogs (wolves, foxes, jackals) and the elephants (elephants, mammoths, mastodons). All members of a family trace their lineage back to a founding matriarch or patriarch. All cats, for example, from the smallest house kitten to the most ferocious lion, share a common feline ancestor who lived about 25 million years ago.
Homo sapiens, too, belongs to a family. This banal fact used to be one of history’s most closely guarded secrets. Homo sapiens long preferred to view itself as set apart from animals, an orphan bereft of family, lacking siblings or cousins, and most importantly, without parents. But that’s just not the case. Like it or not, we are members of a large and particularly noisy family called the great apes. Our closest living relatives include chimpanzees, gorillas and orang-utans. The chimpanzees are the closest. Just 6 million years ago, a single female ape had two daughters. One became the ancestor of all chimpanzees, the other is our own grandmother.
Skeletons in the Closet
Homo sapiens has kept hidden an even more disturbing secret. Not only do we possess an abundance of uncivilised cousins, once upon a time we had quite a few brothers and sisters as well. We are used to thinking about ourselves as the only humans, because for the last 10,000 years, our species has indeed been the only human species around. Yet the real meaning of the word human is ‘an animal belonging to the genus Homo’, and there used to be many other species of this genus besides Homo sapiens. Moreover, as we shall see in the last chapter of the book, in the not so distant future we might again have to contend with non-sapiens humans. To clarify this point, I will often use the term ‘Sapiens’ to denote members of the species Homo sapiens, while reserving the term ‘human’ to refer to all extant members of the genus Homo.
Humans first evolved in East Africa about 2.5 million years ago from an earlier genus of apes called Australopithecus, which means ‘Southern Ape’. About 2 million years ago, some of these archaic men and women left their homeland to journey through and settle vast areas of North Africa, Europe and Asia. Since survival in the snowy forests of northern Europe required different traits than those needed to stay alive in Indonesia’s steaming jungles, human populations evolved in different directions. The result was several distinct species, to each of which scientists have assigned a pompous Latin name.
2. Our siblings, according to speculative reconstructions (left to right):
Homo rudolfensis (East Africa); Homo erectus (East Asia); and Homo neanderthalensis (Europe and western Asia). All are humans.
Humans in Europe and western Asia evolved into Homo neanderthalensis (‘Man from the Neander Valley), popularly referred to simply as ‘Neanderthals’. Neanderthals, bulkier and more muscular than us Sapiens, were well adapted to the cold climate of Ice Age western Eurasia. The more eastern regions of Asia were populated by Homo erectus, ‘Upright Man’, who survived there for close to 2 million years, making it the most durable human species ever. This record is unlikely to be broken even by our own species. It is doubtful whether Homo sapiens will still be around a thousand years from now, so 2 million years is really out of our league.
On the island of Java, in Indonesia, lived Homo soloensis, ‘Man from the Solo Valley’, who was suited to life in the tropics. On another Indonesian island – the small island of Flores – archaic humans underwent a process of dwarfing. Humans first reached Flores when the sea level was exceptionally low, and the island was easily accessible from the mainland. When the seas rose again, some people were trapped on the island, which was poor in resources. Big people, who need a lot of food, died first. Smaller fellows survived much better. Over the generations, the people of Flores became dwarves. This unique species, known by scientists as Homo floresiensis, reached a maximum height of only one metre and weighed no more than twenty-five kilograms. They were nevertheless able to produce stone tools, and even managed occasionally to hunt down some of the island’s elephants – though, to be fair, the elephants were a dwarf species as well.
In 2010 another lost sibling was rescued from oblivion, when scientists excavating the Denisova Cave in Siberia discovered a fossilised finger bone. Genetic analysis proved that the finger belonged to a previously unknown human species, which was named Homo denisova. Who knows how many lost relatives of ours are waiting to be discovered in other caves, on other islands, and in other climes.
While these humans were evolving in Europe and Asia, evolution in East Africa did not stop. The cradle of humanity continued to nurture numerous new species, such as Homo rudolfensis, ‘Man from Lake Rudolf’, Homo ergaster, ‘Working Man’, and eventually our own species, which we’ve immodestly named Homo sapiens, ‘Wise Man’.
The members of some of these species were massive and others were dwarves. Some were fearsome hunters and others meek plant-gatherers. Some lived only on a single island, while many roamed over continents. But all of them belonged to the genus Homo. They were all human beings.