Author : Wahid Ahmad
One
of the key features that differentiates us from other hominins is our face. The
human face is a marvel of evolution, a canvas painted with myriad expressions,
and a reflection of our shared history and individual identity. Welcome to
Anthromedia, in this video we will explore the evolution of the human face over
the last 4 million years. Before we proceed don’t forget to subscribe.
The
human face is a complex skeletal structure formed by 14 bones housing parts of
various systems. To understand the evolutionary changes leading to the modern
human face, we will look at extinct hominin taxa over the past 4 million years
from Ardipithecus to recent hominins.
Chimpanzees,
bonobos, and gorillas have distinct facial characteristics, such as a bony arch
above the eyes that protrudes prominently, separating the facial mask from the
braincase. In contrast, early hominins like Australopithecus show weaker
differentiation between the supraorbital structures above the eyes and the
braincase.
These
differences may be related to both social display mechanisms and biomechanical
performance, with the latter being more important. Among non-human African
great apes, postnatal growth results in a long, vertically deep snout with a
forward-projecting premaxilla, creating a gap between lateral incisors and
canines. Early hominins, including modern humans, exhibit a shorter midface
with a more vertical profile.
From Early Hominins
The
way early hominin faces developed involved independent changes in the upper
jaw, maxillary and front part of the upper jaw called premaxillary. The amount
the face sticks out called prognathism varies due to different growth patterns
and bone changes. The evolved facial features in early hominins happened
because the base of the skull shortened, and the size of canine teeth reduced.
Ardipithecus
ramidus and Australopithecus, our ancient relatives from about 4.4 to 3 million
years ago, had faces that looked different from both modern humans and African
great apes.
Ardipithecus
ramidus had a face with short, light cheekbones like chimpanzees, while
Australopithecus afarensis, including the famous Lucy, had broad and robust
cheekbones. Despite these differences, they shared some features with later
hominins, like us.
Common
features included a short upper jaw, a reduced midface, and supraorbital
structures integrated with the braincase. They also had shorter skulls, less
sexual dimorphism in canine teeth and smaller incisors.
However,
when it came to the parts of the face related to chewing, there were
distinctions. Australopithecus afarensis had a robust chewing system, indicated
by large cheekbones and strong arches, suggesting they had a diverse diet. On
the other hand, Ardipithecus ramidus had a face more similar to chimpanzees,
with vertically short and lightly built cheekbones and arches.
These
facial differences suggest that our early human relatives went through
evolutionary changes in different parts of the face. Initially, changes focused
on the central and upper face, possibly for social signaling. Later changes were
more about adapting the chewing system to different diets.
Australopithecus species, including those classified as Paranthropus, have distinct features in their faces adapted for chewing tough plant foods, especially during arid conditions around 2.8-2.7 million years ago. This is due to robust cheek teeth and mandibular bodies meant for attachment of jaw muscles for powerful vertical biting forces.
From Early Homo
The
faces of three early Homo species are different from australopiths. In early
Homo, the face projection is much less, especially in the area below the nose
called premaxillary region. Certain parts of their faces, like the areas around
the nose, eyes, and cheekbones, tend to face more to the side than earlier
australopiths.
When
we look at early Homo erectus, its face is more similar to modern humans than
to habilis or rudolfensis. It has a more upright face with a nose area that's
pulled back and a noticeable bridge on the nose. It's worth noting that erectus
also has a less robust jawbone compared to australopiths.
As
Homo species evolved, they shifted to a diet involving softer foods, possibly
including meat. This change, starting with early erectus, led to reduced facial
size, indicating a decreased need for large cheek teeth and robust jaws. This
shift may suggest early humans began preparing or tenderizing food, including
meat, before consumption, influencing our evolutionary path.
Middle Pleistocene human species
During
the Middle Pleistocene, Homo underwent evolutionary changes in Eurasia, sharing
facial traits. These Middle Pleistocene hominins are potential ancestors of
Homo sapiens. Identifying the last common ancestor is crucial, predating the
modern human face emergence. The modern face, smaller and non-projecting, with
no supraorbital structures or midfacial prognathism, gradually developed in
Homo sapiens.
Genetic
and morphological data suggest Homo sapiens likely originated in Africa, but
modern face traits may have emerged elsewhere. Researchers focus on key
features, especially the zygomaxillary region. In modern humans, the front part
of the zygomatic bone is like a corner, forming a right angle with the centre
of our face. Also, there's typically a hollow space below the eye, known as the
canine fossa. These unique features contribute to the distinct shape of our
faces.
Researchers
examine if the last common ancestor's zygomaxillary region resembled modern
humans, Neanderthals, or a mix. Homo heidelbergensis, a potential ancestor
seems to lack these features in the zygomaxillary region. Homo antecessor
challenges Heidelbergensis as the last common ancestor, showing sapiens-like
facial features. Fossils suggest primitive Homo antecessor facial morphology
existed in some late Chinese homo erectus and persisted in Homo sapiens in
Africa but was likely lost in Heidelbergensis, rhodesiensis, and Neanderthals
Let's
explore the changes in the human face over time and the possible reasons behind
these adaptations.
The
transition from Middle Pleistocene hominins to modern humans involved facial
changes and gracilization. Adaptive explanations for these changes consider
factors like respiratory and energetic demands, climatic adaptation, diet, and
para-masticatory activity. Shared features in Heidelbergensis and Neanderthals,
such as a large nasal cavity and midfacial configuration, suggest the reduction
of the nasal cavity as a primary cause of midfacial reduction in modern humans.
Neanderthals
exhibit distinctive facial features, including continuous upper jawbone growth
resulting in a protruding face during adolescence. These traits raise questions
about adaptation to extreme cold or genetic drift in small populations.
Factors Affecting Facial Changes
Facial
reduction in modern humans, including brows, midfaces, and jaws, and the
development of a chin, may be responses to altered jaw loading. Despite being
less adapted to sustained chewing, modern humans show increased bite force
compared to Middle Pleistocene hominins, potentially advantageous for
fracturing hard objects. Human facial diversity exceeds that in other primates,
influenced by genetic, climatic, and environmental factors.
Climatic
conditions, especially in high-latitude populations, significantly impact
facial morphology, affecting nasal dimensions and cavity projection. Cultural
and social changes also contribute to facial evolution. The relative reduction
in face size in modern humans is attributed to enhanced social tolerance,
reduced androgen activity, and possibly gestural communication. Reduction in
brow ridge size may enhance communication by enabling a broader range of social
cues.
Predicting
future evolution is challenging, given factors like industrialized diets
impacting facial shape. While change is likely to continue, certain
limitations, such as breathing requirements and jaw function, will influence
the extent of future facial evolution. The human face will adapt as our species
encounters new environmental, social, and cultural conditions, ensuring a
continued evolutionary journey.