Evolution is neither linear nor does it depend on external factors.
Evolution proceeds by quality 'jumps' when certain internal thresholds are reached.
Complex systems have principles of self-organization,
Prologue:
Anne Dambricourt Malassé
MAN HAS BEEN a part of the animal kingdom for more than three million
years. Yet many cultures have seen man as quite separate, or excluded man
entirely, from nature. We see this among monotheistic societies that nurture
theological explanations for the origin of our species. Prior to the Scientific
Revolution, theological considerations served largely to constrain inquiries in
this area. The naturalist movement that emerged during this period enabled some
finally to break free of scriptural assumptions.
Jean-Baptiste Lamarck held the chair in invertebrate zoology at the
Muséum national d’Histoire naturelle (MNHN) in Paris, when he published
Recherches sur l’organisation des corps vivants (Research on the Organization
of Living Bodies) in 1802. This small, but revolutionary, book contained the
first theory of evolution applied to the origins of Homo sapiens. In this view
the progressive straightening of the vertebral column seen in the first
hominids was driven by climatic changes that forced some apes to adopt walking
over arborealism. This idea was then popularized by Charles Darwin in The
Descent of Man, published in 1871. It is now the consensus in
paleoanthropology.
A very different reality is reflected in the collections of the MNHN, on
which I have based my work. On the contrary, straightening, with its correlated
anatomical and psychomotor changes, is an intrauterine process that took place
over the course of more than forty million years. It resulted from a growth in
complexity of the embryonic nervous system and its rotational dynamics, and led
to a succession of threshold effects incompatible with the nested hierarchy of
Linnaean classification.
The identification of the first hominids is flawed.
(…)
NEURAL STRAIGHTENING FROM Australopithecus to Homo is linked to the
development of the nervous system. This explains the straightening of not only
the base of the skull but also the whole vertebral column. The neural tube is
formed by fibers lengthening along its path above the notochord. Complex
movements at stage nineteen of embryonic development, corresponding to the axis
of rotation, can be seen above the point at which the dorsal cord terminates.
Hominization begins precisely at the cephalic limit of the dorsal cord.
Remarkable.
The sole vertebrate embryo in which the dorsal cord extremity is almost
verticalized is that of Homo sapiens. This is a process that began around
thirty-nine million years ago in an Asian species of prosimian that underwent a
contraction in the base of its skull and a declination of its brain stem. This
produced the first degree of neural straightening and cranio-facial contraction
in the simians. Twenty-three million years ago, at least one African species of
small gibbon-like simians underwent further contraction and declination.
This produced the second degree of neural straightening. The embryonic
dorsal cord was almost vertical among many species of great apes, remaining so
until adulthood. This was presumably the case, at least, with respect to
Australopithecus (4.5–1.977 mya). Thereafter the process accelerated, at an
unprecedented rate. The lowered cerebellum and straightened brain stem is that
of Homo sapiens, which Linnaeus named in 1758 and which emerged in East Africa
160,000 years ago. The evolutionary trajectory follows the straightening of the
dorsal cord, but during the first stages of verticalization there was no
dramatic accompanying increase in brain volume. Cranial volume is thus no
longer the benchmark, or rubicon. The benchmark is, in fact, the straightening of
the skull base.
(…)
WHEN AUSTRALOPITHECINE EMBRYOGENESIS emerged around 4 mya, the new
organism was no longer a subspecies of great ape. It did not share a great
ape’s neural embryogenesis, still visible today in gorillas, chimpanzees, and
orangutans. The same is also true for Homo embryogenesis. There is no bone
conformation that can be nested within previous embryonic organizations. The
shapes of the structures are reorganized and innovations have appeared. This
dynamic is typical of emergence in complex systems.
Sapiens embryogenesis is no longer that of any fossil Homo species. The
axial skeleton reveals a new threshold of neural straightening and craniofacial
contraction, with an increased complexity and reorganization of the central
nervous system. The cerebellum is shifted even further toward the front and
down. The occluso-postural equilibrium and the psychomotor development visible
in, for example, Neanderthals, has also changed.
As Buffon and Cuvier observed, there is no unique pattern of anatomical
organization among primates. The idea that there have been gradual
transformations within the limits of a such an organization is absurd. This
would mean that Homo sapiens has gone through all the strata of
evolution—prosimian, ape, great ape, hominin. Homo sapiens is not a prosimian,
nor is it a great ape. The conclusion that Homo sapiens is a primate indicates
that prosimian innovations have been preserved. But it does not signify
evolution within the limits of the same embryonic organization. Sapiens never
passed through the stages of phylogenesis.
Linnaean classification is invisible in our embryogenesis.
If the word Homo must designate the paleoanthropes, then our
embryogenesis is no longer Homo, but sapiens. This is true for each of the five
great embryogeneses, or fundamental ontogeneses, since the emergence of Simian;
each emerged from the preceding one, each time more complex in its neural
organization. Numerous subspecies appear within the limits of the new axial
embryogenesis, with different modes of locomotion and ways of life. Buffon,
Cuvier, de Quatrefages, and Broca were right.
Conclusion
IT IS NOTHING short of remarkable that the ability to create
second-degree stone tools emerged from the threshold of embryonic neural
verticality. This is not an arbitrary boundary for distinguishing between Homo
and other hominins, as is the case with the notion of a cerebral rubicon. The
threshold is objective and allows for the deduction of a reorganization of the
nervous system and its component neuronal networks with the sensors necessary
for controlling the body’s equilibrium. In Homo sapiens, the connections
between the cerebellar and cerebral neocortex are known, and it appears they
participate in high-level cognitive functions, for example memory, dexterity,
language, and reflection. Gestures such as walking and grasping become
conscious with psychomotor development.
The great novelty here is the sudden change in posture of the
cerebellum, and a new neuronal complexity; the cerebellum had to control its
own balance. A new loop of complexity must have developed between the neocortex
of the cerebellum and the brain. These connections could then have favored the
development of new reflective cognitive capacities associated with movements,
those of the hands in particular.
New manual chains of operation reflect a symbolic and conceptual level
of thought attributed to the brain of the genus Homo. My suggestion is that the
emergence of these capacities should be broadened to encompass the hominin
stage, denoted by the verticalization of the cerebellum, such as for
Australopithecus, Kenyanthropus, and Paranthropus. Although their brains were
smaller than that of Homo habilis, they may have been capable of conceptual and
creative innovations. Passing those first thresholds made possible the
creative expression of ideas and concepts.
Crossing the final threshold, Sapiens, amplified those cognitive
properties.
No comments:
Post a Comment