Here's why:
* Common descent is the idea that all living organisms share a common ancestor. This ancestor lived a very long time ago, and over millions of years, its descendants evolved into the diverse species we see today.
* Molecular similarities are strong evidence for common descent. These similarities, such as DNA sequences, protein structures, and metabolic pathways, are essentially inherited from that shared ancestor.
* The more closely related two species are, the more similar their molecules are likely to be. This is because they have had less time to accumulate differences since they diverged from their common ancestor.
Other factors that may contribute to molecular similarities:
* Convergent evolution: Sometimes, unrelated species evolve similar traits due to similar environmental pressures. However, these similarities are usually superficial and not as fundamental as the molecular similarities that point to common ancestry.
* Horizontal gene transfer: This is the transfer of genetic material between organisms that are not directly related through descent. While it can contribute to some similarities, it's not the primary explanation for the widespread molecular similarities observed across diverse species.
In summary, the most compelling explanation for the striking molecular similarities between diverse species is that they all descend from a common ancestor. These similarities provide strong evidence for the theory of evolution and our shared evolutionary history.
