Missing link (human evolution)

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A symbolic portrayal of human evolution, showing developmental stages as a matter of illustration. Human-evolution-man.png
A symbolic portrayal of human evolution, showing developmental stages as a matter of illustration.

"Missing link" is a hypothetical or recently-discovered transitional fossil. It is often used in popular science and in the media for any new transitional form. The term originated to describe the hypothetical intermediate form in the evolutionary series of anthropoid ancestors to anatomically modern humans (hominization). The term was influenced by the pre-Darwinian evolutionary theory of the Great Chain of Being and the now-outdated notion (orthogenesis) that simple organisms are more primitive than complex organisms.

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The term "missing link" has been supported by geneticists since evolutionary trees only have data at the tips and nodes of their branches; the rest is inference and not evidence of fossils.[ citation needed ] However, it has fallen out of favor with anthropologists because it implies the evolutionary process is a linear phenomenon and that forms originate consecutively in a chain. Instead, last common ancestor is preferred since this does not have the connotation of linear evolution, as evolution is a branching process. [1]

There is no singular missing link. The scarcity of transitional fossils can be attributed to the incompleteness of the fossil record.

Historical origins

The term "missing link" was influenced by the 18th-century Enlightenment thinkers such as Alexander Pope and Jean-Jacques Rousseau who thought of humans as links in the Great Chain of Being, a hierarchical structure of all matter and life. Influenced by Aristotle's theory of higher and lower animals, the Great Chain of Being was created during the Medieval period in Europe and was strongly influenced by religious thought. [2] God was at the top of the chain followed by man and then animals. It was during the 18th century that the set nature of species and their immutable place in the great chain was questioned. The dual nature of the chain, divided yet united, had always allowed for seeing creation as essentially one continuous whole, with the potential for overlap between the links. [3] Radical thinkers like Jean-Baptiste Lamarck saw a progression of life forms from the simplest creatures striving towards complexity and perfection, a schema accepted by zoologists like Henri de Blainville. [4] The very idea of an ordering of organisms, even if supposedly fixed, laid the basis for the idea of transmutation of species, for example Charles Darwin's theory of evolution. [5]

The earliest publication that explicitly uses the term “missing link” was in 1844 in Vestiges of the Natural History of Creation by Robert Chambers, which uses the term in an evolutionary context relating to gaps in the fossil record. [6] Charles Lyell employed the term a few years later in 1851 in his third edition of Elements of Geology too as a metaphor for the missing gaps in the continuity of the geological column. [7] It was used as a name for transitional types between different taxa was in 1863, in Lyell's Geological Evidences of the Antiquity of Man . [8]

Haeckel's Chain of the Animal Ancestors of Man Human pedigree.jpg
Haeckel's Chain of the Animal Ancestors of Man

Jean-Baptiste Lamarck envisioned that life is generated in the form of the simplest creatures constantly, and then strive towards complexity and perfection (i.e. humans) through a series of lower forms. In his view, lower animals were simply newcomers on the evolutionary scene. After Darwin's On the Origin of Species , the idea of "lower animals" representing earlier stages in evolution lingered, as demonstrated in Ernst Haeckel's figure of the human pedigree. While the vertebrates were then seen as forming a sort of evolutionary sequence, the various classes were distinct, the undiscovered intermediate forms being called "missing links".

Haeckel claimed that human evolution occurred in 24 stages and that the 23rd stage was a theoretical missing link he named Pithecanthropus alalus ("ape-man lacking speech"). [9] Haeckel claimed the origin of humanity was to be found in Asia. He theorized that the missing link was to be found on the lost continent of Lemuria located in the Indian Ocean. He believed that Lemuria was the home of the first humans and that Asia was the home of many of the earliest primates; he thus supported that Asia was the cradle of hominid evolution. Haeckel argued that humans were closely related to the primates of Southeast Asia and rejected Darwin's hypothesis of human origins in Africa. [2] [10]

The search for a fossil that connected man and ape was unproductive until the Dutch paleontologist Eugene Dubois went to Indonesia. Between 1886 and 1895 Dubois discovered remains that he later described as "an intermediate species between humans and monkeys". He named the hominin Pithecanthropus erectus (erect ape-man), which has now been reclassified as Homo erectus. In the media, the Java Man was hailed as the missing link. For instance, the headline of the Philadelphia Inquirer on February 3, 1895, was "The Missing Link: A Dutch Surgeon in Java Unearths the Needed Specimen". [11]

Famous "missing links" in human evolution

Java Man, the original "missing link" found in Java Pithecanthropus-erectus.jpg
Java Man, the original "missing link" found in Java

Among the famous fossil finds credited as the "missing link" in human evolution are:

Related Research Articles

<span class="mw-page-title-main">Ernst Haeckel</span> German biologist, philosopher, physician, and artist (1834–1919)

Ernst Heinrich Philipp August Haeckel was a German zoologist, naturalist, eugenicist, philosopher, physician, professor, marine biologist and artist. He discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms and coined many terms in biology, including ecology, phylum, phylogeny, and Protista. Haeckel promoted and popularised Charles Darwin's work in Germany and developed the influential but no longer widely held recapitulation theory claiming that an individual organism's biological development, or ontogeny, parallels and summarises its species' evolutionary development, or phylogeny.

<i>Australopithecus</i> Genus of hominin ancestral to modern humans

Australopithecus is a genus of early hominins that existed in Africa during the Pliocene and Early Pleistocene. The genera Homo, Paranthropus, and Kenyanthropus evolved from some Australopithecus species. Australopithecus is a member of the subtribe Australopithecina, which sometimes also includes Ardipithecus, though the term "australopithecine" is sometimes used to refer only to members of Australopithecus. Species include A. garhi, A. africanus, A. sediba, A. afarensis, A. anamensis, A. bahrelghazali and A. deyiremeda. Debate exists as to whether some Australopithecus species should be reclassified into new genera, or if Paranthropus and Kenyanthropus are synonymous with Australopithecus, in part because of the taxonomic inconsistency.

<span class="mw-page-title-main">Peking Man</span> Subspecies of the genus Homo (fossil)

Peking Man is a subspecies of H. erectus which inhabited the Zhoukoudian cave site in modern northern China during the Chibanian. The first fossil, a tooth, was discovered in 1921, and the Zhoukoudian Cave has since then become the most productive H. erectus site in the world. Peking Man was instrumental in the foundation of Chinese anthropology, and fostered an important dialogue between Western and Eastern science for decades to come. The fossils became the centre of anthropological discussion, and were classified as a direct human ancestor, propping up the Out of Asia hypothesis that humans evolved in Asia.

<span class="mw-page-title-main">Eugène Dubois</span> Dutch paleoanthropologist (1858–1940)

Marie Eugène François Thomas Dubois was a Dutch paleoanthropologist and geologist. He earned worldwide fame for his discovery of Pithecanthropus erectus, or "Java Man". Although hominid fossils had been found and studied before, Dubois was the first anthropologist to embark upon a purposeful search for them.

<span class="mw-page-title-main">Transitional fossil</span> Type of fossilized remains

A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.

<i>Meganthropus</i> Hominin fossil

Meganthropus is an extinct genus of non-hominin hominid ape, known from the Pleistocene of Indonesia. It is known from a series of large jaw and skull fragments found at the Sangiran site near Surakarta in Central Java, Indonesia, alongside several isolated teeth. The genus has a long and convoluted taxonomic history. The original fossils were ascribed to a new species, Meganthropus palaeojavanicus, and for a long time was considered invalid, with the genus name being used as an informal name for the fossils.

<span class="mw-page-title-main">Solo Man</span> Extinct subspecies of Homo erectus

Solo Man is a subspecies of H. erectus that lived along the Solo River in Java, Indonesia, about 117,000 to 108,000 years ago in the Late Pleistocene. This population is the last known record of the species. It is known from 14 skullcaps, two tibiae, and a piece of the pelvis excavated near the village of Ngandong, and possibly three skulls from Sambungmacan and a skull from Ngawi depending on classification. The Ngandong site was first excavated from 1931 to 1933 under the direction of Willem Frederik Florus Oppenoorth, Carel ter Haar, and Gustav Heinrich Ralph von Koenigswald, but further study was set back by the Great Depression, World War II and the Indonesian War of Independence. In accordance with historical race concepts, Indonesian H. erectus subspecies were originally classified as the direct ancestors of Aboriginal Australians, but Solo Man is now thought to have no living descendants because the remains far predate modern human immigration into the area, which began roughly 55,000 to 50,000 years ago.

<i>Homo</i> Genus of hominins that includes humans and their closest extinct relatives

Homo is a genus of great ape that emerged from the genus Australopithecus and encompasses the extant species Homo sapiens and a number of extinct species classified as either ancestral to or closely related to modern humans, including Homo erectus and Homo neanderthalensis. The oldest member of the genus is Homo habilis, with records of just over 2 million years ago. Homo, together with the genus Paranthropus, is probably most closely related to the species Australopithecus africanus within Australopithecus. The closest living relatives of Homo are of the genus Pan, with the ancestors of Pan and Homo estimated to have diverged around 5.7-11 million years ago during the Late Miocene.

Paleoanthropology or paleo-anthropology is a branch of paleontology and anthropology which seeks to understand the early development of anatomically modern humans, a process known as hominization, through the reconstruction of evolutionary kinship lines within the family Hominidae, working from biological evidence and cultural evidence.

<span class="mw-page-title-main">Java Man</span> Subspecies of Homo erectus (fossil) discovered on the island of Java in 1891

Java Man is an early human fossil discovered in 1891 and 1892 on the island of Java (Indonesia). Estimated to be between 700,000 and 1,490,000 years old, it was, at the time of its discovery, the oldest hominid fossil ever found, and it remains the type specimen for Homo erectus.

<span class="mw-page-title-main">Taung Child</span> Hominin fossil

The Taung Child is the fossilised skull of a young Australopithecus africanus. It was discovered in 1924 by quarrymen working for the Northern Lime Company in Taung, South Africa. Raymond Dart described it as a new species in the journal Nature in 1925.

<span class="mw-page-title-main">Gustav Heinrich Ralph von Koenigswald</span> German-Dutch paleontologist and geologist (1902–1982)

Gustav Heinrich Ralphvon Koenigswald was a German-Dutch paleontologist and geologist who conducted research on hominins, including Homo erectus. His discoveries and studies of hominid fossils in Java and his studies of other important fossils of south-eastern Asia firmly established his reputation as one of the leading figures of 20th-century paleo-anthropology.

Human taxonomy is the classification of the human species within zoological taxonomy. The systematic genus, Homo, is designed to include both anatomically modern humans and extinct varieties of archaic humans. Current humans have been designated as subspecies Homo sapiens sapiens, differentiated, according to some, from the direct ancestor, Homo sapiens idaltu.

<span class="mw-page-title-main">Trinil</span> Palaeoanthropological site in Java, Indonesia

Trinil is a palaeoanthropological site on the banks of the Bengawan Solo River in Ngawi Regency, East Java Province, Indonesia. It was at this site in 1891 that the Dutch anatomist Eugène Dubois discovered the first early hominin remains to be found outside of Europe: the famous "Java Man" specimen.

<span class="mw-page-title-main">Pithecometra principle</span>

The Pithecometra principle or Pithecometra thesis describes the evolution of humans; the pithecometra law is analogous to the concept that "man evolved within apes" or "man descended from apes" as advocated by Thomas Henry Huxley.

<i>Homo erectus</i> Extinct species of archaic human

Homo erectus is an extinct species of archaic human from the Pleistocene, with its earliest occurrence about 2 million years ago. Its specimens are among the first recognizable members of the genus Homo.

<span class="mw-page-title-main">Hominidae</span> Family of primates

The Hominidae, whose members are known as the great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera: Pongo ; Gorilla ; Pan ; and Homo, of which only modern humans remain.

<span class="mw-page-title-main">Mojokerto child</span> Hominin fossil

The Mojokerto child, also known as Mojokerto 1 and Perning 1, is the fossilized skullcap of a juvenile early human. It was discovered in February 1936 near Mojokerto by a member of an excavation team led by Ralph von Koenigswald. Von Koenigswald first called the specimen Pithecanthropus modjokertensis but soon renamed it Homo modjokertensis because Eugène Dubois – the discoverer of Java Man, which was then called Pithecanthropus erectus – disagreed that the new fossil was a Pithecanthropus. The skullcap is now identified as belonging to the species Homo erectus.

<span class="mw-page-title-main">Anthropopithecus</span> Obsolete primate taxon

The terms Anthropopithecus and Pithecanthropus are obsolete taxa describing either chimpanzees or archaic humans. Both are derived from Greek ἄνθρωπος and πίθηκος, translating to "man-ape" and "ape-man", respectively.

<i>Ape to Man</i> Dramatised documentary on the finding the missing link in evolution

Ape to Man is a dramatised documentary on the scientific community's journey to find the missing link in human evolution, between our ancestors the apes and modern man today.

References

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  2. 1 2 Reader, John (2011). Missing Links: In Search of Human Origins . Oxford University Press. ISBN   978-0-19-927685-1.
  3. Lovejoy, Arthur O. (1964). The great chain of being : a study of the history of an idea : the William James lectures delivered at Harvard University, 1933. Harvard University Press. ISBN   0674361539. OCLC   432702791.
  4. Appel, T. A. (1980). "Henri De Blainville and the Animal Series: A Nineteenth-Century Chain of Being". Journal of the History of Biology. 13 (2): 291–319. doi:10.1007/bf00125745. S2CID   83708471.
  5. Snyder, S. "The Great Chain of Being". Archived from the original on 2017-07-28.
  6. Chambers, Robert; Ireland, Alexander (1884). Vestiges of the Natural History of Creation. W. & R. Chambers.
  7. Lyell, Sir Charles (1851). A Manual of Elementary Geology: Or, The Ancient Changes of the Earth and Its Inhabitants, as Illustrated by Geological Monuments. Murray.
  8. Lyell, Sir Charles (1863). The Geological Evidence of the Antiquity of Man. John Murray. Geological Evidences of the Antiquity of Man.
  9. Haeckel, Ernst (1874). The Evolution of Man.
  10. Klein, Richard G. (2009-09-22). "Darwin and the recent African origin of modern humans". Proceedings of the National Academy of Sciences. 106 (38): 16007–16009. Bibcode:2009PNAS..10616007K. doi: 10.1073/pnas.0908719106 . ISSN   0027-8424. PMC   2752521 . PMID   19805251.
  11. "The Missing Link: A Dutch Surgeon in Java Unearths the Needed Specimen" (PDF). Philadelphia Inquirer. February 3, 1895.
  12. Wood and Richmond; Richmond, BG (2000). "Human evolution: taxonomy and paleobiology". Journal of Anatomy. 197 (Pt 1): 19–60. doi:10.1046/j.1469-7580.2000.19710019.x. PMC   1468107 . PMID   10999270. p. 41: "A recent reassessment of cladistic and functional evidence concluded that there are few, if any, grounds for retaining H. habilis in Homo, and recommended that the material be transferred (or, for some, returned) to Australopithecus (Wood & Collard, 1999)."