Final answer:
The claim that evolutionary biologists cannot explain the evolution of cilia is false. Theories like the endosymbiotic gene fusion and contributions from ancestral prokaryotic structures suggest explanations for the evolution of such complex structures.
Step-by-step explanation:
The statement suggesting that evolutionary biologists still cannot explain how a cilium could have arisen is false. The hypothesis of endosymbiotic gene fusion, as presented by James Lake, supports the evolution of eukaryotic cells. This concept posits that eukaryotes developed from a merging of genetic material between Archaea and Bacteria, with evidence shown by some eukaryotic genes resembling those of Archaea while others resemble those of Bacteria.
Regarding cilia evolution, the ancestral cytoskeletal system is thought to have had the capability to make cilia/flagella, and this system has evolved to consist of complex structures like eukaryotic microtubules, which play a role in the motion of cilia and flagella. There are several theories, including the one that suggests membrane proliferation and compartmentalization may have contributed to the development of various cell organelles. Spirochete bacteria and other prokaryotic ancestors are hypothesized to have contributed structures that led to cilia and flagella in eukaryotes.
It is also important to note that scientific understanding continues to evolve with new research. Although there may be some controversy in the details, the evolutionary theory overall provides a robust framework for understanding the development of complex structures in living organisms, including eukaryotic cilia.