The most controversial model , known as viral eukaryogenesis , posits that the membrane @-@ bound nucleus , along with other eukaryotic features , originated from the infection of a prokaryote by a virus . The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands , mRNA capping , and tight binding to proteins ( analogizing histones to viral envelopes ) . One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular " predator " . Another variant proposes that eukaryotes originated from early archaea infected by poxviruses , on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes . It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis .