Universal common ancestry

Universal common ancestry is the idea that all life on Earth is related, having descended from a common ancestor or ancestral gene pool. It is a tenet of the Theory of evolution, and a belief rejected by Creationism.

History

Universal common ancestry is an ancient idea. Many ancient pagans held that humans were related to animals. Anaxagoras, for instance, argued that humans are related to fish, but became humans because the water became too crowded, and the fish kicked humans out of the water. Many ancient American Indian cultures also believed humans were descended from animals, and some commomorated these beliefs through totem poles.

More recently, in the 18th and 19th centuries, the idea of universal common ancestry regained popularity in Europe. In 1745, French mathematician and scientist Pierre-Louis Moreau de Maupertuis (1698-1759) wrote in his book Venus Physique:

"Could one not say that, in the fortuitous combinations of the productions of nature, as there must be some characterized by a certain relation of fitness which are able to subsist, it is not to be wondered at that this fitness is present in all the species that are currently in existence? Chance, one would say, produced an innumerable multitude of individuals; a small number found themselves constructed in such a manner that the parts of the animal were able to satisfy its needs; in another infinitely greater number, there was neither fitness nor order: all of these latter have perished. Animals lacking a mouth could not live; others lacking reproductive organs could not perpetuate themselves... The species we see today are but the smallest part of what blind destiny has produced..."

Charles Darwin further popularized the idea with his book, Origin of Species, in which he wrote:

"[P]robably all of the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed."

"The whole history of the world, as at present known, ... will hereafter be recognised as a mere fragment of time, compared with the ages which have elapsed since the first creature, the progenitor of innumerable extinct and living descendants, was created."

"When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Silurian system was deposited, they seem to me to become ennobled."

Bases for belief

Belief in common descent is largely derived from the similarity among forms of life. For example:

• All cells are bound by a membrane
• All cells store heritable information as DNA.
• All cells adhere to the same basic mechanism of gene expression.
• All cells utilize the same metabolic pathways.
• All cells have ribosomes to produce protein.

From these similarities, an evolutionist infers that all life is related through one original life form.

Bases for disbelief

Creationists argue that the inference of common ancestry cannot reasonably be drawn from the evidence, for two reasons:

• Similarity is not meaningful evidence of common ancestry
• Differences which cannot be explained by evolutionary mechanisms are powerful evidence against common ancestry.

To illustrate the first objection, one might argue that all cars are related because they have four tires, an internal combustion engine, a steering wheel, etc. However, obviously cars are not related; they simply share common design characteristics. In the same way, creationists argue that just because humans and plants both have cell membranes is no more evidence of common ancestry than it is of common design.

The second objection relies on incidents of irreducible complexity and specified complexity to point to the unlikelihood that all life forms diversified through variation and selection alone. They point to issues such as:

• The transition from non-self-reproducing chemicals to self-replicating cells: the process of self-replication requires an enormous number of components be present in the cell for it to function at all, and none of the components required for self-replication serve any purpose unless all are present simultaneously; therefore it is unreasonable to conclude that abiogenesis occured without design.
• The transition from asexual reproduction to sexual reproduction: male reproductive organs are incredibly complex, and serve no purpose unless female reproductive organs (which are equally, if not more, complex) already exist. Therefore the sexes could not have evolved in a step-wise fashion, because neither set of reproductive organs would serve any purpose unless the other set already existed.

For the above reasons, creationists conclude that there is insufficient evidence to support the conclusion of common ancestry. They further conclude that baraminology provides a much more meaningful way of studying the origin of life, because it allows for the possibility that some forms of life are related, but without the rather extraordinary presumption that all forms of life are related.