Hominins vs Hominids

Since the time that humans began to seek alternative answers to their origins, other than that of Divine creation, the subject of evolution has been a complex one, often raising more questions than answers. From the Age of Enlightenment onwards, a more scientific approach to human ancestry directed theories away from more metaphysical thinking, and the taxonomic system, introduced in 1753 by Carolus Linnaeus, helped to establish a clearer framework in which to operate.

In the early 1800s, Jean-Baptiste Lamarck’s work on the transmutation of species paved the way for Charles Darwin and Alfred Russel Wallace to expound the theory further, culminating in the work On the Origin of Species, which has become the foundation of all subsequent theory and thinking on the subject. However, as with any science, there were gaps in the knowledge and certain errors that have required addressing over the intervening years. Darwin, for example, knew nothing of genetics and was not even aware of continental drift, among other issues that could have greatly influenced his work.

It is in the very nature of science to test theories, replacing them with new ones if or when required. This is all well and good within a laboratory when dealing with chemistry, physics or biology. But evolution is notoriously difficult to test as the fossil record of hominids is sparse. Much of the theory of human evolution is just that – theory. These theories have been updated and improved as scientific techniques and equipment have become more efficient and our knowledge and understanding has increased, but any changes within the study of human evolution are often infuriatingly slow to gain full acceptance across the academic and scientific world.

The Family Tree Of Species

The furore that Darwin’s publication caused when launched in 1859 is not something we can readily appreciate from our modern perspective. Here was a man who openly suggested that apes and humans were somehow related. The very notion of Natural Selection was shocking to Victorian sensitivities. But the fact that this seminal work is still referred to and remembered today helps to illustrate its impact on the world. Many significant alterations to this theory have been made since then, though few people would be able to name either the person responsible or the breakthrough they discovered. Some of these changes have caused as much consternation and debate within the scientific community as Darwin’s original work did within the world in general at the time, shifting whole sections of the family tree of species and requiring fundamental changes to teaching and textbooks.

In spite of the changes and improvements to the theory, the overriding fact at the heart of the evolutionary process is that if you travel back far enough in time you can identify branches in the family tree that connect all species. The problem inherent within this system is the sparsity of fossil evidence, along with the plethora of names required to identify each separate species, not to mention the colossal distances in time involved.

So when new terms are introduced, it can add to the confusion – especially to those outside the fields of palaeontology and palaeoanthropology. And one example of this is the use of the words hominins and hominids.

Hominid or Hominin?

To keep track of all the different species, each newly identified fossil skeleton is given a label. This sounds simple in practice, but the label often has to specify several factors:

• Kingdom
• Phylum
• Class
• Order
• Superfamily
• Family
• Tribe
• Genus
• Species

Some also include ‘sub-family’ categorisation. Not all of these names are used all the time, however. Take modern humans, for example, usually referred to by genus (homo) and species (sapiens).

The Full Classification Of Humans

Traditionally, however, the full classification of humans was as follows –

Kingdom – Animalia

Phylum – Chordata

Class – Mammalia

Order – Primates

Superfamily – Hominoidea

Family – Hominidae

Genus – Homo

Species – Sapiens

At the ‘superfamily’ level under the traditional system, chimps, gorillas, orangutans and gibbons were separated into further categories.

Other Genetic Links

As advances were made in the study of DNA and genetics, however, it became apparent that there was a closer genetic link between humans, gorillas and chimpanzees than was previously thought. These latter two species once sat within the wider group of ‘great apes’, with the family specification of pongidae. Due to the fact that chimpanzees share around 99.4% of the same genomes, it was proposed that chimps be given the label homo troglodytes. This was met with a clamour of disapproval, however, and so the term hominidae was broadened to include chimps, gorillas and orangutans, though orangutans remained within the genus pongo. This led to the reclassification of humans to include the subfamily homininae and the tribe hominini, which includes chimpanzees (gorillas split from the family hominidae into their own tribe and genus of gorillini and gorilla).

The Denisova Cave Hominin Called Denny

After the discovery of hominin bone fragments it became apparent that some of these sub species had at some point mated with one another and “hybrid” species existed like “Denny” which you can read about in my other article about the Denisova Caves in Russia.

What’s in a name?

It has been well over a decade since the new classification has come into effect, but the old information remains in countless textbooks, is still taught in colleges and universities, and even appears on many websites. So, does it matter if we refer to hominids as hominins, or vice versa? After all, the ‘nesting’ nature of the taxonomic system means that many of our extinct ancestors (now referred to as hominins) fall within the hominidae family.

The simple answer to this is that while it is acceptable, it isn’t as specific. The best way to remember the current classification is this:

Hominids

This group contains all of the Great Apes – both extinct and modern, including modern humans, gorillas, chimpanzees, orangutans and their immediate ancestors.

Hominins

This group refers to modern humans as well as extinct human species and ancestors, including Australopithecus, Homo, Ardipithecus and Paranthropus.

The New System Of Classification

In order to gain a better understanding of the ‘new’ system, it helps if you are aware of some of the conventions involved in the taxonomy. For example, words ending in ‘-idae‘ always refer to the family. Where you have an ‘-inae‘ ending, it will relate to the sub-family, and names that end in ‘-ini‘ will denote the tribe. It is important to note that ‘tribe’ in this instance is purely a biological specification designating a split between genus and subfamily, and does not refer to social divisions, which needs to be stressed when communicating this information to students.

Meet the ancestors

To help get the message across, you might find that some websites are very helpful when presenting information regarding human evolution.

Where the term hominin is used, they put ‘human relative’ by the side of it in brackets.

Having established the difference between the two terms and understood the reasoning behind it, we can take a look at some of our ancestors and get a better idea of the challenges facing palaeontologists.

Australopithecus

In general, most hominin species have been located in the north-central, eastern and southern regions of Africa, giving rise to the ‘Out of Africa’ theory which proposes that all modern humans originated here (though more recent discoveries have cast some doubt on this, such as the 110,000 year old homo sapiens jawbone found in China). Of these species, those that fall within the Australopithecus genus are the most important, as it is believed that the genus homo is directly descended from them. The name Australopithecus, meaning ‘Southern Ape’, was first applied by Raymond Dart in 1924, when he identified Australopithecus Africanus. The fossil specimen was a child’s skull, incomplete, but bearing marked humanoid features, and therefore regarded as a very early ancestor of humans, at 2-3 million years old.

Bipedal Australopiths

Australopiths – ranging from between 4.2 to 1.9 million years old – displayed qualities that separated them from primates; upright walking and bipedal; shorter, broader pelvis to provide balance and better propulsion over the ground; lack of opposable toes, with rigid transverse arches, and feet positioned directly beneath the knees.

The Wastebasket Taxon

Coupled with differences in brain capacity and the size and configuration of the teeth, these features helped to establish such a wide range of genera that the term Australopithecus has been deemed the ‘wastebasket taxon’. This somewhat unkind sounding label indicates the fact that many of the fossil remains are placed in the genus because of their physiological similarities, as opposed to any firmly established ‘family’ connection.

One fact that drives this is that the fossil record is fragmentary. Although thousands of hominid remains have been excavated, there are few whole skeletons. Much of what you view in museums around the world, aside from being replicas, will be based on reconstructions using a degree of extrapolation and applied guesswork.

Lucy The Hominid

Take ‘Lucy’, for example, posited as possibly the most important of the hominids discovered in Africa. At 3.2 million years old, she was the oldest hominin ever found, and – with about 40% of the skeleton present – the most complete. This in itself highlights the problem with identifying fossil bones. Most discoveries involve far fewer bones, often only fragments.

Armed with a better understanding of hominins vs hominids, perhaps we can also appreciate the difficulties facing those dedicated palaeontologists and palaeoanthropologists who spend a lifetime furthering our knowledge of human ancestry.