8. Modern Homo

‘Modern Homo’ considers evidence about the origin and subsequent migrations of anatomically modern humans, or Homo sapiens. What features of the skeleton are only found in modern humans? When and where do we find the earliest fossil evidence of modern humans? Did the change from pre-modern Homo to modern humans happen several times and in several different regions of the world? Or did anatomically modern humans emerge just once, in one place, and then spread out, either by migration or by interbreeding, so that modern humans eventually replaced regional populations of pre-modern Homo across the world?

6. Archaic and transitional hominins

‘Archaic and transitional hominins’ considers the fossil species that almost certainly belong to the hominin clade, but which are still a long way from being like modern humans. The fossils that share more of their morphology with modern humans than they do with chimpanzees and bonobos, yet do not show the changes in jaw and tooth size and in body size and shape that characterize hominin species we are more comfortable with, including within our own genus Homo, are called ‘archaic’ hominins. The group of hominins that seem to be part archaic hominin and part Homo are called ‘transitional’ hominins.

5. Early hominins

During the period from 8–5 million years ago, the Earth experienced the beginning of a long-term drying and cooling trend. Due to the increasing dryness, forests were replaced with open woodland, and areas of grassland began to appear. Hominin evolution began in Africa at the time of these climatic changes. ‘Early hominins: possible and probable’ reviews four collections of fossils that represent each of the ‘candidate’ species that have been put forward for being at the base of the hominin clade: Sahelanthropus tchadensis dated to 7.2–6.8 mya; Orrorin tugenensis dated to round 6 mya; Ardipithecus kadabba dated to 5.7–5.2 mya; and Ardipithecus ramidus from round 4.5 mya.

4. Fossil hominins

Palaeoanthropologists use many methods to work out the significance of newly discovered fossil evidence, but the first task is to assign hominin fossils to a taxon. After that researchers work out that taxon’s relationships with other fossil and living taxa, and then they infer the behaviours and habitat preferences of the taxon. ‘Fossil hominins: analysis and interpretation’ explains the workings of classification and taxonomy. It describes how whole fossils can be reconstructed from fragments; the difficulties of determining the sex and developmental age of hominin fossil remains; the different interpretations of speciation; how cladistics analysis works; and the gaps and biases in the hominin fossil record.

1. Introduction

All living organisms are situated on a Tree of Life that began around three billion years ago. The Introduction explains that this VSI focuses on the last stage of the human evolutionary journey, the stage between the most recent common ancestor shared by chimpanzees/bonobos and modern humans (around six to eight million years ago) and present-day modern humans. The three objectives of this VSI are to try and explain how palaeoanthropologists go about the task of improving our understanding of human evolutionary history; to convey a sense of what we think we know about human evolutionary history; and to show where the major gaps in our knowledge are.

9. The future of human evolution

What are the next few decades likely to bring in terms of new evidence about human evolution? Are modern humans still evolving, and if so, what changes are we likely to see? ‘The future of human evolution’ considers both of these questions. It explains that researchers will continue to look for additional fossil evidence, at existing fossil sites as well as in new locations. Both will provide valuable evidence. It considers the chances of finding new taxa and how more evidence can be squeezed out of the existing fossil record through improved molecular biology and imaging techniques. Finally, it looks at contemporary human evolution and what is likely to influence the future of our species.

7. Pre-modern Homo

So when and where in human evolutionary history do we see the earliest evidence of creatures that are more like modern humans? ‘Pre-modern Homo’ considers the species that many hominins researchers are comfortable with recognizing as members of the genus Homo. It looks at the earliest fossil evidence of pre-modern Homo from Africa, and then follows Homo as it moves out of Africa into the rest of the Old World. It begins with Homo ergaster, dated to around 2 mya, and then moves on to Homo erectus, which was found in sites in Africa, China, and Indonesia. Other pre-modern Homo species include Homo heidelbergensis; Homo naledi; Homo floresiensis; and Homo neanderthalensis.

3. Fossil hominins

‘Fossil hominins: their discovery and context’ discusses what the hominin fossil record consists of, how it is discovered and recovered, and how it and its context are investigated, which includes the processes of dating fossils and reconstructing past environments. It reviews the evidence that can be used to investigate what the 6–8 million-year-old hominin clade looks like. How much of it can be reconstructed by looking at variation in modern humans, and what needs to be investigated by searching for, finding, and then interpreting fossil and archaeological evidence? How do researchers decide where to look for new fossil sites, and how do they date any fossils they find at those sites?

2. Finding our place

When did the process of using reason to try and understand human origins begin, and how did it develop? When was the scientific method first applied to the study of human evolution? ‘Finding our place’ begins by reviewing the history of how first philosophers and then scientists came to realize that modern humans are part of the natural world. It then explains why, using advances in molecular biology, scientists think chimpanzees and bonobos are more closely related to modern humans than they are to gorillas, and why they think the common ancestor of the chimpanzee/bonobo and modern human clades lived between six and eight million years ago.