Have you ever wondered? How have we changed? Much or little? Here we will answer these questions.
DIET AS A SELECTIVE AND EVOLUTIONARY FACTOR
Human populations live adapted to their environment, and diet has a lot to say in this aspect. For example, those living in South East Asia do not eat the same food as those in Siberia. The previous fact is something to consider because people’s diet explains what their habitat is like, how these people exploit their habitat, and their chances of survival given that a population eats what is available, even though it may make distinctions in terms of tolerance to certain foods. For these reasons, it can be said that there is ecology in the sphere of food and that it is transmitted from generation to generation.
Remember that the goal of every organism or species is completing its life cycle, that is, to survive and reproduce (biological efficiency or fitness). Consequently, all factors -such as nutrition- that affect this goal have a great and direct relevance for the organism or species. It has been proven that inadequate nutrition is capable of producing physiological disorders that alter the maturation and use of the fertile period in women because such malnutrition can be responsible for delayed menarche (first menstruation), early menopause, prolonged postpartum amenorrhoea, and increased infant and intrauterine mortality (miscarriages).
Since the discovery of agriculture and animal husbandry, the diet has been a major selective factor. It has led to great changes in humans (think of examples such as lactose or starch digestion). Our diet has had a huge impact on us, to the point that we are more different from our ancestors than they were from theirs. And this, even though we belong in the same genus. Why is this? You will find out below.
EARLY HOMO: WHO ARE THEY?
First of all, do we humans descend from monkeys? No!
It all started in the Rift Valley (Africa), where some 6 and 8 million years ago, high volcanic activity formed mountain ranges that trapped the disturbances from the Atlantic. As a result, rainfall became less abundant, and what was rainforest gradually became savannah. Our ancestral species lived there, and some of its populations became separated by these mountain ranges. Over time, they would give rise to today’s chimpanzees (adapted to the rainforest, to hanging from trees) on the one hand and, on the other, to the first Homo (adapted to the savannah). This separation took place about 2 million years ago.
Understanding past phylogenetic relations is complicated and anthropologists are in charge of studying them. For now, take a look at the following proposal to gain context.
Source: Animal Biology, Ecology, Parasitology, Edaphology, and Agricultural Chemistry, Anthropology Unit, University of Salamanca. 2019.
EARLY HOMO: WHAT DID THEY EAT? WHY?
As many studies indicate, dietary change played a major role in the origin and early evolution of our genus in Africa (Ungar, P., 2006), but this understanding of human evolution has improved rapidly in recent decades thanks to the large-scale cataloguing of genomic variability in both modern and archaic humans. Besides, considering and understanding the environmental factors that drove human adaptation is challenging, but it is known that 2-3 million years ago, there was a marked change in climate, with much less precipitation, so our pre-Homo ancestors faced drier, more open habitats (savanna expansion).
To survive in this emerging landscape, our ancestors needed the ability to move quickly and adapt. Among other adaptations emerged the ability to act in groups and safeguard offspring and the most vulnerable group members from large predators, both day and night. Thus, the food environment also changed, since primates could no longer rely on a plentiful supply of fruit but had to capture and eat different types of animals, as well as roots and tubers. (James, W. P. T., 2019).
The study, headed by Ungar, and published in the Annual Review of Anthropology in 2006, reviews and evaluates some recent models of early Homo dietary adaptations in the context of the fossil record (skeletal remains of early Homo), the archaeological record (faunal and lithic remains) and the evidence of environmental dynamics (changes in the climatic and pluviometric regime, as well as changes in ecosystems and habitats) during the Plio-Pleistocene, and they set out the following points:
MEAT INTAKE
The role of meat consumption in human evolution continues to dominate the current literature, although there are different perspectives. However, the basic idea to be clear about is the following:
The green-bordered arrows indicate the closing and repetition of this feedback loop many times. As a consequence, there is an increasing consumption of meat and fat that allows brain development and, with this, that of knowledge and interactions with other individuals (for example, the division of labour and the sharing of food).
PLANT INTAKE
Some authors suggest that the diet of early Homo included more xeric plants (tubers, roots, corms and bulbs) and that gathering was a driving force in human evolution. They also state that tools were first more likely used to collect and process plants. It is impossible to know the proportion of meat as opposed to vegetables in the early Homo diet, but, in general, plants represent 60%-70% of the human diet
The study’s main limitation is to exactly know what they ate. Yet, it seems that early Homo jaw and teeth finds can help us clarify some questions about the diet of these remote species. We offer more details at the end of this article.
COOKING IN THE PAST
Data from the Carmody, R. & Wrangham, R., 2009 study suggest that early Homo used non-thermal processing methods, such as pounding. This means that they pounded the food hard and repeatedly, and this provided them with a significant increase in energy gain over unprocessed raw diets. This may have contributed to supporting energetically costly adaptations that first emerged in Homo habilis, such as increased body and relative brain size.
Afterwards, there was a turning point in human evolution caused by the diet itself, due to the control and mastery of fire, which enabled cooking food.
Cooking brought additional benefits -such as starch gelatinisation, protein denaturation, and killing food-borne pathogens– that were not easily achieved by non-thermal treatments. Cooking is an evolutionarily significant event. The energetic and textural impacts of cooking seem consistent with morphological adaptations indicating a high dietary quality in H. erectus (which is consistent with the hypothesis that cooking began with this species).
EVIDENCE OF PAST DIETS
Fossil remains have been and still are one of the most studied elements that, together with genetic and paleoclimatic evidence, provide knowledge about our evolutionary line. All three aspects are necessary and complement each other in this complex task of unravelling our most remote past.
Understanding the order and age of the different fossil finds is a very complicated task, because they are only found very occasionally and, obviously, they are usually pieces of body parts and in remote places. It can be said to be a kind of global puzzle where scientists from all over the world search for the intricacies by playing with fossil remains and genetic and paleoclimatic data.
Now, if we find a fossil and are fortunate enough that it is a jawbone (that will indicate dietary characteristics), what features should we focus on?
TOOTH SIZE
Anterior (front) teeth are fatter in early Homo than in their ancestors and in more modern Homo species. This indicates changing selective pressures with increasing use of tools to prepare food before ingestion.
TOOTH SHAPE
In principle, wear on the molar (back) teeth suggests hard diets (uncooked food).
ENAMEL THICKNESS
An adaptation to avoid tooth breakage, especially in diets with hard food. Early Homo had molars with relatively thick enamel, which has become progressively thinner (with cooking, hard foods are no longer eaten).
BIOMECHANICS OF THE JAW
The shape of the jaw reflects the forces acting on it during chewing, potentially providing clues to the mechanical properties of the food eaten by early prehistoric humans.
TOOTH MICRO-STRIAE
Microscopic wear on molar teeth is related to the type of diet.
CHEMISTRY OF MINERALISED TISSUES
Isotope and trace element analysis.
Finally, patterns of genetic variation provide clues from our past towards adaptation to the new diets that had to be acquired to survive different environmental changes. For example, the variation in the number of copies of the amylase (saliva enzyme) gene, the persistence of lactase (the enzyme that breaks down lactose in milk), the perception of bitter taste, the propensity to some haemoglobinopathies, or the local amplification of FADS genes, which are responsible for the synthesis of long-chain polyunsaturated fatty acids (James, W. P. T., 2019).
