Mixed Up Bones

Mixed Up Bones

Most people picture paleontologists digging up complete, or nearly complete skeletons that show the step-by-step progress of human evolution. There's an old Fat's Waller song that comes to mind:

The toe bone's connected to the foot bone,
The foot bone's connected to the ankle bone,
The ankle bone's connected to the leg bone,
Now shake dem skeleton bones!
The leg bone's connected to the knee bone,
The knee bone's connected to the thigh bone,
The thigh bone's connected to the hip bone,
Now shake dem skeleton bones!

That's how we picture fossils. They come out of the ground with all the pieces, and if not connected, the bones were at least close to each other. However, this is far... VERY FAR from what actually happens.

Bones used to assemble a skeleton many come from locations separated by several feet, or at times up to a mile or more.

Bones from a variety of animals and marine life, and including both ape and human bones, are frequently found all jumbled together. Scientists pick which bones go with which animal, and not all scientists pick the same bones. In some cases a skeleton is put together based more on a desire for the fame and fortune that comes with finding a new transitional form, than it is based on what those bones actually represent.

Let's take a look at some of the famous "transitional" fossils in the human lineage.

Homo Habilis Fossils

Homo Habilis

"This species, one of the earliest members of the genus Homo, has a slightly larger braincase and smaller face and teeth than in Australopithecus or older hominin species. But it still retains some ape-like features, including long arms and a moderately-prognathic face."

The above quote, describing Homo habilis, is the introductory paragraph of the Smithsonian's web page about Homo habilis. Because it has a combination of ape and human features, it is thought to be in the lineage between Australopithecines (apes) and Homo erectus (human). But here's the rest of the story quoted from "Contested Bones" by Christopher Rupe and Dr. John Sanford.

"Ever since the naming of Habilis, there has been disquiet within the paleoanthropology community regarding whether or not Habilis was a sound species, and belonged in the genus Homo. The striking ape-like qualities of Habilis led many to conclude that Habilis bones are of the ape-type, not the human-type." - (page 160)

"Virtually all of the bones attributed to Habilis were found as isolated bones or bone fragments. None of the bones were found physically connected to other bones." - (page 164)

"The murky definition of what Habilis is has led to the uncritical inclusion of any unknown bones into the Habilis group. It is no wonder leading experts like Tattersall and Schwartz describe Habilis as an 'all-embracing watebasket species into which a whole heterogeneous variety of fossils could be conveniently swept.'" - (pages 164-165)

"Numerous lines of evidence suggest that Habilis is an invalid species, the product of active imaginations and fossil beds with both ape and human bones." - (page 169)

"The invention of a 'new species' by combining bones from different species has occurred several times in the field of paleonanthropology. Paleo-experts acknowledge that it is not uncommon for hominin-bearing sites to contain a commixture of Homo and Australopithecus bones." - (page 172)

Homo Habilis Skull Image credit: Nachosan, CC License.

mixed up bones

Homo floresiensis - Homo erectus - Fully Human

A common problem with fossils attributed to the human lineage is that they are assembled from fossils beds containing both ape and human fossils. The result can be a fossil that is a mixture of ape and human bones and this, of course, looks like a transitional fossil. But there is more. There are two other factors that lead to mischaracterization of fossils as ape-human transitions: pathologies and normal variation.

Homo floresiensis is so small that it is also known as "The Hobbit." Found in Indonesia, floresienis stood just 3 feet 6 inches tall, had short femur bones (legs), and a cranial capacity of 420 cm3. Here was a new human species that lived 18,000 years ago. Or was it?

It's interesting that there are pygmies living near the site where the Hobbit was found. The conditions on the island lead to a pathologies resulting from island dwarfism, inbreeding, and reductive selection, collectively referred to as insular dwarfism Insular dwarfism is a well-known condition among mammals. It is described in the book "Contested Bones:"

"Mammals living on an island can become smaller over generations. This is typically seen in island-dwelling species with access to a limited food supply. Such dwarfed populations are reproductively isolated many generations, and must survive for long periods, undernourished and in very small populations." - (page 88)

The result is inbreeding, genetic drift, and deleterious mutations with selection favoring small size (as seen in the pygmies living there now). Homo floresiensis is fully within the known physical variation of humanity, with the pathologies expected from insula dwarfism.

Home erectus

"While Erectus is clearly human, it is not a normal human. Erectus was very much like Neanderthal--but displaying evidence of various pathologies. Many Erectus skulls are disturbing-0-showing diverse abnormalities and asymmetrics." - (page 55)

"There is strong evidence that the bones commonly referred to as Homo erectus are fully human individuals who suffered from various pathologies associated with such things as inbreeding, miutation, teratogens (developmental abnormalities), etc... Indeed, most of the classic features attributed to Erectus--including those found in the skull and face--have been found in modern humans." - (page 77)

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