Functional and morphological stasis during molecular evolution.

This research examined and compared the evolutionary changes in certain proteins present in humans, mice and horses, and observed that despite a significant degree of molecular evolution, the functionality and structure of these proteins remained largely unchanged. This supports the theory of neutral alleic drift proposed by Kimura.

Study Methodology

• The researchers conducted an evolutionary comparison between two sets of proteins: human beta 2-microglobulin and its mouse equivalent, as well as human and horse alpha-globin.
• They utilized techniques conceived by prominent scientists Miyata, Yasunaga and Kimura to assess the evolutionary distance between these proteins, which refers to the changes in these proteins since they diverged from their common ancestor species.
• Two methods were used to estimate this evolutionary distance: the Miyata and Yasunaga’s method gave two values for evolutionary distance (KS and KA), while Kimura’s method gave one value for the same (K).

Findings

• A significant degree of molecular evolution was observed in beta 2-microglobulin since its divergence from the common ancestor of mice and humans. The values of evolutionary distance were both high and low (K = 0.353 by Kimura’s method, KS = 0.708 and KA = 0.171 by Miyata and Yasunaga’s method).
• For human and horse alpha-globin, the values were lower but still suggested some degree of evolution (K = 0.152, KS = 0.293, and KA = 0.084).
• Despite these nuances in evolutionary differences, the study found that the functionality and structure of these proteins (form or morphology) remained largely unchanged. For instance, mouse beta 2-microglobulin could effectively influence the expression of HLA class I antigens on human-mouse hybrid cells, and the tertiary structures of human and horse deoxyhemoglobin were almost identical.

Implications

• The results of this study contribute to supporting Kimura’s theory of neutral alleic drift, which suggests that most molecular evolution comes from genetic drift of neutral alleles rather than natural selection. Despite the observed molecular evolution, the ability of the studied proteins to perform their designated functions remain intact.
• This study highlights the resilience and adaptability of biological systems, illustrating the fact that, despite significant evolutionary changes at the molecular level, the structure and function of essential proteins can remain stable.