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 inhabiting our planet.
Not only we have an abundance of uncivilized cousins ( chimps, Apes, etc.), once upon a time, we had quite a few brothers and sisters as well ( other human species).
So who were our Siblings?
Before getting into the intricacies, Let’s understand how biologists name any organism and what these words, ‘genus’ and ‘species’ really mean?
Animals are said to belong to the same species if they tend to mate with each other, giving birth to fertile offspring. For example, Horses and donkeys have a recent common ancestor and share many physical traits. But they show little sexual interest in one another. Thus these two can be distinctly considered as two different species.
Species that evolved from a common ancestor are bunched together under the name ‘genus’ (plural: genera). For example, lions, tigers, leopards, and Jaguars are different species within the genus Panthera.
Biologists name organisms with a two-part Latin name, genus followed by species. Thus lions, for example, are called Panthera leo, the species leo of the genus Panthera. Seemingly, whoever reading this write-up now is a Homo Sapien – The species (wise) of the genus Homo (man).
Genera, in turn, are grouped into families such as cats (Lions, cheetahs, house cats), the dogs (wolves, foxes, jackals). All members of a family trace their lineage back to a founding ancestor. For example, all cats from the smallest house kitten to the most ferocious lion, share a common feline ancestor who lived about 25 million years ago.
We Homo sapiens, too, belongs to a family. You like it or not, the truth is that we are all members of a large and a particularly noisy family called the great apes. our closest relatives include chimpanzees, gorillas, and orangutans. However, the chimpanzees are the closest.
Now, let’s get to know our siblings.
Image showing all the species belonging to genus ‘ Homo’ (source : geneticliteracyproject.org)
Image showing an earlier genus of apes called Australopithecus (source: es.dino.wikia.com)
Humans first evolved in East Africa about 2.5 million years ago from an earlier genus of apes called Australopithecus, which means ‘Southern Ape’.
Image showing bands of Australopithecus (source: http://www.inverse.com)
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 ( speciation), to each of which scientists have assigned a pompous Latin name.
Image showing Homo neanderthalensis (source: Human Origins – Smithsonian Institution)
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.
Image showing Homo erectus (source: Human Origins – Smithsonian Institution)
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 long-lasting human species ever. This record is unlikely to be broken even by our own species. It is doubtful whether we 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’, a subspecies of Homo erectus, was suited to life in the tropics.
Image showing a unique species Homo floresiensis (source: Human Origins – Smithsonian Institution)
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 phenomenally 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.
Image showing the comparison between Homo erectus & Homo floresiensis (source:http://www.rappler.com/science-nature/26485-homo-floresiensis-anthropology-question)
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. (However, It’s status is as either species or subspecies, it currently carries the temporary names Homo sp. altai, or Homo sapiens ssp. denisova)
Who knows how many lost relatives of ours are waiting to be discovered in other caves, on other islands, and in other climates?
Image showing Homo rudolfensis (source: http://www.flickr.com/photos/schmerles)
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’,
Image showing Homo ergaster (source: howhumanshaveevolved.weebly.com)
Homo ergaster, ‘Working Man’, and eventually our own species, which we’ve immodestly named Homo sapiens, ‘Wise Man’. But all of them belonged to the genus Homo. They were all human beings.
It’s a common misconception to envision these species as arranged in a straight lineage of descent, with Ergaster begetting Erectus, Erectus begetting the Neanderthals, and the Neanderthals evolving into us. This linear model gives the mistaken impression that at any particular moment only one type of human-inhabited the earth, and that all earlier species were merely older models of ourselves. The truth is that from about 2 million years ago until around 10,000 years ago, the world was home, at one and the same time, to several human species. And why not? Today there are many species of foxes, bears, and pigs.
Source: Most Mysterious Extinct Human Species!
Thus, the earth of a hundred millennia ago was walked by at least six different species of man.