Why is glycolysis considered one of the earliest evolved metabolic pathways?

Glycolysis is considered one of the earliest evolved metabolic pathways primarily because it lacks organelles or specialized structures, operates independently of oxygen, and is present in a wide range of organisms, from bacteria to humans.

Lack of Organelles: Glycolysis occurs in the cytoplasm of cells and does not require specialized organelles such as mitochondria or chloroplasts. This simplicity suggests that glycolysis could have evolved early in the history of life when cells were simpler and lacked complex internal structures.

Oxygen Independence: Glycolysis is anaerobic, meaning it does not require oxygen to proceed. This characteristic suggests that glycolysis likely evolved before oxygen became abundant in the Earth's atmosphere. Early Earth had limited oxygen, so metabolic pathways that did not rely on oxygen would have been advantageous for early life forms.

Ubiquity Across Organisms: Glycolysis is a highly conserved pathway found in virtually all organisms, from prokaryotes to eukaryotes. Its widespread presence indicates that glycolysis likely evolved very early in the evolution of life and has been retained throughout evolutionary history due to its fundamental role in cellular metabolism.

Overall, the simplicity, oxygen independence, and ubiquity of glycolysis across various organisms support the idea that it is one of the earliest evolved metabolic pathways.