Does All Life Have the Same Distant Ancestor?

The idea that all life on Earth evolved from a common ancestor is a cornerstone of modern biology. Molecular biology provides some of the strongest evidence for this theory. One of the most compelling lines of evidence is the concept of DNA sequence homology.

Understanding DNA Sequence Homology

Homology in biology refers to the similarity between certain features of different organisms due to a single evolutionary origin. In the context of DNA, it means that specific DNA sequences in different organisms are somewhat similar to their alleged distantly related ancestors. This similarity suggests that the DNA in question was slowly mutated and inherited as it passed from one generation to another.

To illustrate, let's consider a simple scenario where a set of characters represents a sequence of DNA that undergoes gradual changes:

Original Sequence: "We took a boat."
First Generation: "He took a boat."
Second Generation: "She took a bat."
Third Generation: "Hey look a bat."
Final Generation: "They looked at a bat."

The changes in each generation are subtle but convey a fitness advantage over time, much like DNA mutations that provide a survival advantage. The areas of similarity in the original and final sentence, such as "took a," are analogous to conserved DNA sequences in different organisms.

Conserved Genes and Signal Transduction Pathways

Similar to a conserved sentence, conserved genes and their products, proteins, play a critical role in life's machinery. One such example is the signal transduction pathways. These pathways involve a series of molecular events that enable a cell to respond to external signals. A famous example is the JAK/STAT signaling pathway, which is highly conserved across various organisms from simple planaria to complex humans.

Consider the following signal transduction pathway:

A ligand molecule from outside the cell binds to a protein receptor embedded in the cell membrane. This binding causes the receptor to activate another protein. The activated protein then activates another protein, and this cascade continues until the final protein, a transcription factor, is activated. The activated transcription factor binds to a specific gene, which then leads to the production of an mRNA, and subsequently, a protein.

This pathway is not only conserved at the gene level but also at the system level. For instance, the JAK/STAT pathway is present in many organisms, from planaria and worms to flies and human beings.

Developmental Gene Regulatory Networks (dGRNs)

Compared to single genes and cellular pathways, the concept of Developmental Gene Regulatory Networks (dGRNs) is more complex. dGRNs are networks of master transcription factors that control the overall development of an organism. These transcription factors regulate which genes are turned on or off, ultimately dictating the characteristics of the organism.

A schematic diagram of a sea urchin dGRN illustrates this complexity. Each black letter in the diagram represents a cascade of events, with each cascade setting off another until the entire organism is formed. This network is idiosyncratic, with small changes potentially leading to catastrophic effects, much like changing a critical component in a complex machine.

The Limits of Evolution

If evolution cannot gradually alter small, specific pathways, it certainly cannot create new dGRNs and new types of organisms. This argument suggests that the complexity of life, particularly at the organizational level, cannot be achieved through natural processes alone. Instead, it hints at the need for a sentient designer.

The idea that life was designed by an extremely intelligent being is a compelling alternative to the notion of common descent. While this perspective is highly philosophical, it remains a topic of much debate in both science and religion.

To learn more about this sentient designer, consider starting by reading the Gospel according to John, which provides a detailed account of His attributes and desires.