How much hair?
Comparing modern humans with other living primates can help us work out how hairy our ancestors may have been. Unfortunately hair does not fossilise!
Modern humans are very sparsely haired compared to other primates, except perhaps for the hair on our heads, which can be quite thick. Our closest living relatives, the chimpanzees, have much hairier backs and chests than we do but, even so, they are not considered to be very hairy when compared with other primates.
Our earlier ape-like ancestors were probably more similar to chimpanzees than to modern humans with regard to their hairiness. However, the bodies of our more recent ancestors were probably more similar to our own and covered in very sparse hair. The hairy covering of our early African ancestors would have provided some insulation from heat stress. Hairless bodies, however, are considerably more affected by high temperatures. To help counter this increased heat stress, our ancestors’ bodies began to develop a different method of cooling the body – one related to sweating. Many scientists believe that the change in hairiness and ability to cool the body by sweating, occurred at least 1.9 million years ago, with the appearance of Homo ergaster.
What colour skin?
To work out the probable skin colours of our ancestors, scientists have studied the skin colours of modern humans and other living primates.
The benefits of having dark-coloured skin
When the skin is exposed to intense UV radiation from the sun, a number of adverse health conditions can result, including:
- skin cancer
- a deficiency of folic acid vitamins, leading to anaemia, infertility and/or birth defects.
People with darker skin are less likely to be affected by these conditions because the dark pigment in their skin blocks some of the harmful radiation and this is why most tropical peoples today have a darker skin colouring.
Our earliest ancestors probably had a thicker covering of hair which would have given them protection from the sun. When our bare-skinned ancestors evolved in Africa, their skin became more exposed to the sun and a darker skin colour would have been an important adaptation for reducing the effects of ultraviolet (UV) radiation from the intense sun of the tropics.
The benefits of having light-coloured skin
When our ancestors left the tropical regions of Africa they met very different environmental conditions. The areas further away from the tropics receive less UV radiation and under these conditions, dark skin was a disadvantage. Instead, light skin became important as it allowed more UV radiation to penetrate the skin and be made into vitamin D, which is essential for bone development and a healthy immune system. Another benefit of light coloured skin is that it is better able to tolerate colder temperatures than dark skin and is less susceptible to frost bite. This would be an advantage in colder climates such as those found in northern Europe.
Populations who have remained in the one environment for thousands of years have skin colours adapted to their particular environment. The modern migrations of people around the world means many people are now living in environments to which their skin colour is not suited. Over thousands of years, the skin colours of these migrant populations would naturally change to adapt to the new environments, but our technology and cultural practices, including the use of sunscreens, clothing and shelter, are likely altering this natural adaptation of skin colour.
What type of body shape?
Once fossils are prepared and preserved, the bones are assembled and a detailed drawing or reconstruction is made of the remains. Experts are then used to recreate the possible physical appearance of the hominin.
In most cases, a nearly complete skull is required to reconstruct facial features and a partial skeleton, especially with some limb bones, is needed to recreate height, body build and possible movement capabilities (leg bones essentially carry a skeleton so looking at the length, size and strength of these bones provides clues as to how a hominin moved). However, for fragile or incomplete remains, particularly skulls, CT scans (computerised tomography) can help create a virtual 3D image and then a plastic cast.
Muscles, tendons, fat tissues and skin are then added to recreate a living hominin. Fleshing out a skull or skeleton gives us a better understanding of how they looked and moved. Experts use marks on fossil bones to help them reattach soft tissues, as these reveal where the tissues attached and how strong they may have been. They also use educated guesses based on dissections of primates and forensic anthropology techniques, particularly for determining the thickness of tissues.
The growth of technology has introduced the digital age of hominin reconstruction. Computer programs blend cutting-edge wizardry with traditional techniques of drawing and sculpture to bring new realism to the movement and behaviour of our ancestors.
A face from the past
At the top is a reconstruction of a creature that lived in east Africa about 1.9 million years ago. It is modelled on a famous skull known as KNM-ER 1470 which was found at Koobi Fora, Kenya in 1972. Hundreds of small, fossilised bone fragments were recovered before this work of reconstruction could begin.
The work to reconstruct KNM-ER 1470 (Homo rudolfensis) was begun by Meave Leakey. She had to sort through hundreds of fossil bone fragments but gradually reassembled a partial skull using more than 150 pieces.
Completing the skull
Most of the skull was reassembled using the fragments collected from the discovery site but some parts of the skull were still missing. To reconstruct the entire skull, the missing parts were filled-in with modelling clay.
On some specimens the reconstruction of missing parts is a simple task that can be achieved by copying the features from one side of the body to the other. The task becomes more complex when an individual is missing an entire feature, such as the jaw or both cheek bones. In this case, it may be possible to copy the feature from other individuals of the same species. Otherwise, scientists have to rely on a detailed knowledge of anatomy to determine the appropriate shape and size of the missing feature.
Adding soft tissues
The muscles and other tissues such as nose cartilage, fat deposits and the eyes can now be added. Marks on the bones show where the muscles once attached and also provide clues about how bulky these muscles were. The general size and shape of the nose can be worked out using the structure of the surrounding bones as well as the size and shape of the nasal opening. However, the exact details of the nose will remain unknown. The correct eye colour is also debatable.
Completing the picture
Skin and hair are added to complete the reconstruction but these are often the most debatable aspects. Our ancestors’ skin colour and degree of hairiness is determined by comparisons with living primates.