The cell’s fundamental molecules are universal

In addition to the DNA code, there are other fundamental molecular processes that appear to be common to all life. One intriguing example is DNA replication which copies both strands of the DNA molecule, but in different directions. Evolution predicts these fundamental processes to be common to all life. Indeed this was commonly said to be an important successful prediction for the theory. As Niles Eldredge explained, the “underlying chemical uniformity of life” was a severe test that evolution passed with flying colors. (Eldredge, 41) Likewise Christian de Duve declared that evolution is in part confirmed by the fact that all extant living organisms function according to the same principles. (de Duve, 1) And Michael Ruse concluded that the essential macromolecules of life help to make evolution beyond reasonable doubt. (Ruse, 4)

But this conclusion that the fundamental molecular processes within the cell are common to all species was superficial. In later years, as the details were investigated, important differences between species emerged. For example, key DNA replication proteins surprisingly “show very little or no sequence similarity between bacteria and archaea/eukaryotes.” (Leipe) Also different DNA replication processes have been discovered. These results were not what were expected:

In particular, and counter-intuitively, given the central role of DNA in all cells and the mechanistic uniformity of replication, the core enzymes of the replication systems of bacteria and archaea (as well as eukaryotes) are unrelated or extremely distantly related. Viruses and plasmids, in addition, possess at least two unique DNA replication systems, namely, the protein-primed and rolling circle modalities of replication. This unexpected diversity makes the origin and evolution of DNA replication systems a particularly challenging and intriguing problem in evolutionary biology. (Koonin)

Some evolutionists are reconsidering the assumption that all life on Earth shares the same basic molecular architecture and biochemistry, and instead examining the possibility of independent evolution, and multiple origins of fundamentally different life forms. (Cleland, Leipe)

References

Cleland, Carol. 2007. “Epistemological issues in the study of microbial life: alternative terran biospheres?.” Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences 38:847-861.

de Duve, Christian. 1995. Vital Dust. New York: BasicBooks.

Eldredge, Niles. 1982. The Monkey Business. New York: Washington Square Press.

Koonin, E. 2006. “Temporal order of evolution of DNA replication systems inferred by comparison of cellular and viral DNA polymerases.” Biology Direct 18:1-39.

Leipe, D., L. Aravind, E. Koonin. 1999. “Did DNA replication evolve twice independently?.” Nucleic Acids Research 27:3389-3401.

Ruse, Michael. 1986. Taking Darwin Seriously. New York: Basil Blackwell.