Reasons to Believe

X’s and Z’s Point to Creation

Dr. Hugh Ross and Dr. Fazale ("Fuz") Rana

Many people claim that the case for biological evolution is unassailable; that overwhelming evidence exists for common ancestry. Yet, if life’s history is explicable exclusively through evolutionary processes, then scientific observations should match evolutionary expectations.

One example of failed expectations is the phenomenon known as convergence. And scientists from MIT and the Washington University School of Medicine have uncovered another troubling example of convergence: the X and Z chromosomes of humans and chickens, respectively.1

Convergence describes instances in which unrelated organisms possess nearly identical anatomical and physiological characteristics. Evolutionary biologists assert that convergence results when natural selection channels the random variations believed to be responsible for evolutionary change along similar pathways to produce similar features in unrelated organisms.

Yet, this explanation doesn’t make sense from within the evolutionary paradigm. If evolution is indeed responsible for the diversity of life, one would expect convergence to be extremely rare. The mechanism that drives the evolutionary process consists of a large number of unpredictable, chance events that occur one after another. Given this mechanism and the complexity and finetuning of biological systems, it seems improbable that disparate evolutionary pathways would ever lead to the same biological feature in organisms manifesting different biological structures and/or living in different habitats.

Yet this appears to be the case. As evolutionary biologist Simon Conway Morris points out in his book Life’s Solution, convergence is a widespread feature in the biological realm. And The Cell’s Design documents and describes over one hundred examples of convergence at the biochemical level.

This recent work concerned the origin of the sex chromosome. In mammals, females have two copies of the X chromosome (XX) and males have one copy of the X and one copy of the Y chromosome (XY). The opposite is the case for birds, with males having two copies of the Z chromosome (ZZ) and females possessing one copy of the Z and one copy of the W chromosome (ZW).

According to the traditional evolutionary model, sex chromosomes evolved from one of the other chromosomes (autosomes) with the Y and W chromosomes, respectively, undergoing deterioration and the loss of genes. The X and Z chromosomes were thought to remain relatively unchanged.

Detailed characterization of the human and chicken X and Z chromosomes, however, reveals a different scenario. When viewed from an evolutionary standpoint, it looks like both the X and Z chromosomes underwent several identical changes independently:

(1) gene acquisition, increasing the number of genes on the chromosome;

(2) acquisition of noncoding DNA (LINE DNA), decreasing the gene density; and

(3) increased expression of genes in the testes.

In this context, it is noteworthy that one of the changes to the X and Z chromosomes is the increased content of LINE DNA. Molecular geneticists have shown that [this class of noncoding DNA plays a role in controlling gene expression in mammalian females through Barr Body formation.

In other words, it appears as if the X and Z chromosomes in mammals and birds followed the same evolutionary pathway, yielding virtually the same outcome, a result that doesn’t make sense within the evolutionary paradigm.

Convergence and the Case for Intelligent Design

Though the idea of convergence fits awkwardly within the evolutionary framework, it makes perfect sense if a Creator is responsible for life. Instead of convergent features emerging through repeated evolutionary outcomes, they could be understood as reflecting the work of a Divine mind. The repeated origins of biological features equate to the repeated creations of an intelligent Agent who employs a common set of optimal solutions to address a common set of problems facing unrelated organisms.


1. Daniel W. Bellott et al., “Convergent Evolution of Chicken Z and Human X Chromosomes by Expansion and Gene Acquisition,” Nature 466 (July 29, 2010): 612–16.

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. Read more about Dr. Hugh Ross.