Since we are the only surviving species of hominin, we can only find out from fossils and archaeological finds about our evolutionary past since the separation with the chimpanzees.

Using radiometric dating and geological methods (in which layer was the fossil found and what do we know about this layer?) scientists can find out about the approximate age of a fossil.

But it is difficult to find out how the individual fossils are related to each other. Are two finds of the same species or should they be classified into different species? This is easier to answer if the finds have very different characteristics (including genetic traits), seemingly lived very far apart in time, and were found in completely different regions of the earth.

But often it is not so easy to answer. It also depends on how one defines the term “species”. Usually, individuals are considered to belong to a species if they can breed together and produce fertile offspring. But we do not know exactly who has been mating with whom throughout our evolutionary history, especially when “species” lived around the same time and in the same region. From DNA analysis, for example, we know that some of us have “Neanderthal DNA” in us. Apparently, some of our Homo sapiens ancestors have mated with Neanderthals – and yet a distinction is made between the species Homo neanderthalensis and Homo sapiens.

Therefore, the differentiation of species or subgroups in Hominini is more or less fluent, and sometimes it is difficult to put them into distinct categories. Also, there are different interpretations with each newly discovered fossil. Thus, the views of different scientists about the phylogenetic relationships between the Hominini differ.

And so there are also different evolutionary trees that depict relationships in different ways or indicate the degree of certainty that scientists have about relationships.