Introduction
Evolution of life on earth can be defined as ‘the process of development in which an organ or organism becomes more and more complex by the differentiation of its parts; a continuous and progressive change according to certain laws and by means of resident forces’. After the unknown origin of life on earth, organisms survived, reproduced, diversified and adapted into complex forms through evolution. Charles Darwin, a renowned biologist, documented several observations on nature and the survival of life on his voyage on the HMS Beagle to explore South America and the Galapagos Islands. In his book, ‘On the Origin of Species’, Darwin defined natural selection as the process whereby species and organisms evolve over time, enhancing their adaptation to their environment to increase survival and reproduction. In humans, natural selection operates through daily activities essential for survival.
Natural selection is the outcome of four common phenomena:
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Variation among the organisms and species;
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Genetic heritability causing some variations;
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Differential reproductive success within organisms and species;
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Adaptation to thrive, survive and reproduce.
The evolution of humans has been a long chain of events for several million years, making us unique from other species, with the face being one such feature. It is influenced by our need to eat, breathe, see and communicate. Face plays a significant role in signalling more than twenty emotions by contraction or relaxation of muscles. The face is composed of 14 bones and about 20 main muscles, which have evolved over a period of time immemorial as a part of adaptation and survival. Complexity in the development of the face and several natural, biological and environmental factors results in certain features developing or becoming rudimentary based on the needs of different eras.
Why do orthodontists need to know about the evolution of the human craniofacial region?
The comparative data of skeletal forms of modern urbanised human and ancestral fossil skulls show considerable variations in terms of skeletal and dental malocclusions, with the latter showing negligible evidence of malocclusion (crowding, impactions). Evolutionary morphological, biological, and cultural adaptations have made humans bipedal, enhancing their reasoning abilities, expressive faces, smiles, and communication. However, the increased brain size was compensated with jaw size reduction, weakened masticatory muscles and shortened faces, leading to specific dentofacial derangements, further complicated by differences in the origin and development of these components, which makes humans vulnerable to developing malocclusions and serious health problems like Obstructive Sleep Apnoea (OSA), primarily from epigenetic and other environmental reasons. It is imperative for orthodontists to understand the evolutionary changes in human faces and how these changes have contributed to the increasing prevalence of malocclusion in modern humans.
Evolution of humans
As famous geneticist Theodosius Dobzhansky described, ‘Nothing in biology makes sense except in the light of evolution’. It is prudent to note that the told and untold secrets of the present-day human body lie somewhere in the light of evolution.
Humans didn’t evolve instantaneously. The immediate evolutionary family of modern humans is comprised of the hominoids, which include the ‘lesser apes’ (siamangs and gibbons) and the ‘great apes’ (orangutans, gorillas, bonobos and chimpanzees). Our closest relatives, the chimpanzees and bonobos (pygmy chimpanzees), have 98% similarity to human DNA when compared to single nucleotide polymorphism. The human lineage, known as Hominins, separated from the great apes around 6 million years ago. Hominin Australopithecus were the first to walk upright. , Genus Homo appeared around 2 million years ago and the only surviving species from the genus, Homo sapiens , arrived approximately 0.2 million years ago. However, different human species didn’t appear in a linear chain but rather in a web way, resulting in several forms of species overlapping in existence at different times in different parts of the world till around 10,000 years ago.
One of the most dynamic, powerful and radical factors that changed our bodies is cultural evolution, which is not by chance but by learned intention. It is relatively rapid and may produce considerable influence on changes in our bodies. The agricultural revolution started around 12,000 years ago when humans preferred farming to forage for food and the later industrial revolution occurred around the 18th century when humans started using machines to replace human work.
Some of the characteristic features of different hominin lineage are tabulated in Table 10.1 .
TABLE 10.1
Characteristic features of different hominin lineage
| S no. | Hominin lineage | Characteristic features |
|---|---|---|
| 1 | Genus Ardipithecus |
One of the oldest hominins with sufficient fossil evidence
Ape-like skull with brain size similar to chimps (300 cc) Vertically short, lightly built zygomatic arches Shorter bowl like pelvis with a more upright posture unlike apes Mainly tree living as having long forearms and fingers with grasping first toe (Hallux). However, they were bipedal whenever on the ground Smaller canine than apes but larger and sharper than later hominins probably indicating aggressiveness |
| 2 | Genus Australopithecus |
Terrestrial bipeds continued to use trees for food and protection at night. This combined terrestrial and arboreal strategy made them persist for long (3 million years)
More lateral prominence and larger zygoma with flaring arches Slight brain size increase (400–500 cc) Pelvis and locomotive limbs are more like humans but with long forearms with curved fingers for tree climbing Canines became blunt and small, but molar teeth were considerably larger and had thicker enamel, indicating that the consumption of raw hard plantations needed considerable chewing efficiency |
| 3 | Homo habilis |
Oldest member species, mainly found in East Africa
Habilis means ‘Handyman’, Made tools from stone and bone Used cutting stone tools to butcher meat and cut animal bones, requiring less chewing Cranial capacity was 640 cc Molars again became smaller due to less required masticatory efficiency. Canines remained blunt and small |
| 4 | Homo erectus |
The first human species to venture throughout Africa and Eurasia
Ecologically highly flexible with cognitive development to thrive in different places with different environments (cranial capacity 1250 cc) for a long time Completely bipedal7 First Homo to reveal facial shortening, canine blunting and reduced mandibular robusticity |
| 5 | Homo heidelbergensis | Very much similar in body proportion, dental pattern and cognitive ability to modern humans.Pioneer of hunter gatherer culture. Made sophisticated tools and aware of the controlled use of fire |
| 6 | Homo neanderthalensis |
Probably evolved from
Homo heidelbergensis
or a separate variant of
Homo sapiens
. Recent studies have evidenced portions of the Neanderthal genome carried by non-African humans
Mainly lived in Europe and Asia and in extreme cold climatic conditions Cranial capacity is almost similar to modern humans (1450 cc) Stout body stature and complex behaviour possessed some form of language skill Large and prominent jaws with carnivore food style Increased size of nasal cavity, and paranasal sinuses and no hard roofing of the lacrimal duct made them highly adaptable to breathing cold air , |
| 7 | Homo sapiens |
Very high cranial capacity (1500 cc)
Known for finer tool making, complex social activities and clever hunting technique Originated in Africa but excellent cognitive ability allowed global expansion to Eurasia, America and Australia by adapting to different climatic conditions The onset of agriculture, domestication of animals, socialisation and urbanisation Relatively short face due to shortening with the appearance of canine fossa |
In short, the hominins have undergone five major evolutionary transformations through lineages.
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Divergence from apes and evolving to upright bipedals.
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Genus Australopithecus evolved greater adaptation to forage for and ate a variety of food apart from fruits.
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During evolution, genus Homo had striking similarities to the modern human body and a larger brain to become hunter gatherers about 2 million years ago.
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Hunter-gatherers widely spread across the planet and evolved even bigger brains and larger, more slowly growing bodies.
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Species Homo sapiens, or modern humans, evolved exceptionally larger cranial capacities for communication, culture and reasoning abilities with socialisation that allowed them to disperse rapidly across the globe and to become the only surviving human species on the planet.
Morphological differences such as smaller and less projectile jaws, larger calvaria, smaller and blunted teeth, and biped or orthograde humans distinguish them from early hominins. The evolution of modern humans from great apes ( Fig. 10.1 ) is characterised and strongly influenced by four main features:
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The transition from quadrupedalism to bipedalism
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Blunting of canine teeth
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Shortening of facial prominence
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Increase in cranial capacity.
A graphical representation showing the gradual reduction in the facial prominence and an increase in the cranial capacity from chimpanzee to modern humans.
A graphical representation showing the transition from quadrupedalism to bipedalism.
Evolutionary changes in dental arch and palate. A graphical representation showing the morphological changes from a long dental arch with spaced dentition to a short arch with no interproximal spaces.
Graphics drawn based on the concept of Pontzer H. Overview of Hominin Evolution. Nature Education Knowledge. 2018;3(10):8.
The mandible evolved with the appearance of the chin, the formation of the curve of Spee due to the arcial growth of the mandible ( Fig. 10.2 ) and the formation of a secondary joint as the temporomandibular joint (TMJ).
Changes in the arcial growth of the lower jaw.
The arch has been gradually closed in modern man, with the line pointing upward and forward unlike upward and backward in earlier species.
Graphics drawn based on the concept of Sambataro S, Fiorillo L, Bocchieri S, Stumpo C, Cervino G, Herford AS, Cicciù M. Craniofacial Evolution: From Australopithecus to Modern Man. J Craniofac Surg. 2022 Jan-Feb 01;33(1): 325-332. doi:10.1097/SCS.0000000000007841 . PMID: 34267119.
The bipedalism and head orientation
Bipedalism is a transformation in the locomotion of tetrapods from four to two rear limbs and the ability to walk upright ( Fig. 10.3 ). This characteristic is a hallmark of human evolution, and humans are the only habitually striding (not hopping), tailless and featherless bipedal creatures.
A silhouette representation showing the transition from quadrupedalism to bipedalism.
Graphics drawn based on the concept of The Bipedalism Hypothesis in Human Evolution. ThoughtCo. Updated January 01, 2018.
Accessed May 16, 2025. Available from: thoughtco.com/the-bipedalism-hypothesis-human-evolution-1224799.
A more balanced attachment between the skull and spinal column helps in upright posture and locomotion. The spinal column was parallel to the floor, with the foramen magnum posteriorly placed in quadrupeds. However, in bipeds, the spinal column changed to a perpendicular position from the ground, and the foramen magnum gradually migrated anteriorly to the centre of the base of the cranium for improved balance and centre of gravity ( Fig. 10.4 ).
Shift of foramen magnum to more anteroinferior to maintain balance in bipeds.
(A) Skull of a gibbon
Source: Berkovitz B, Shellis P. Primates. In: Berkovitz B, Shellis P, editors. The teeth of mammalian vertebrates. Academic Press; 2018. https://doi.org/10.1016/B978-0-12-802818-6.00009-0 . (B) Skull of a modern human.
This evolutionary change is responsible for freeing the forelimbs to carry out other physical, social and cultural activities and enabling the modern human with the following utilities:
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Carrying and using tools by free forelimbs
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More energy saving than quadrupeds from a biomechanical point of view
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Better thermoregulation by reducing exposure to ultraviolet radiation of the sun
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Sexual dimorphism for infant carriage and food carriage
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Helps to orient the head for a straight elevated binocular vision for protection and food when humans moved from jungle to savanna.
Complete bipedal locomotion requires an upright posture, supported by a straight neck pointing downwards instead of backwards. In quadrupeds, the neck is oriented obliquely and pointed backwards with a very strong musculature group. The head functions by a cantilever mechanism that has a high range of motion across all planes of space. In humans, the neck musculature is short and weak, and it has a lower range of motion, especially in flexion and extension movements. However, the hominin skull has a straight and binocular vision during bipedal movement, which could have evolved by natural selection during the transition in the environment from jungle to savanna.
The development of orbital orientation for straight binocular vision in bipedalism may be explained by three important angular relationships :
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Neck orientation relative to earth horizontal (FH Plane)
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Angle of foramen magnum relative to the cranial base
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Angle of cranial base.
A quadruped primate like a chimp becoming a biped, some visual axis issues would arise. The cranial base of a chimp is 25 degrees flatter than the cranial base of humans. The angle of foramen magnum plane and orbital plane is 65–70 degrees in chimps but 100 degrees in modern humans. Thus, the chimp orbits point forward in habitual quadruped posture but will point upward in bipedal posture unless the chimp flexes the neck considerably ( Fig. 10.5 ).
