Final answer:
The early mitochondria-containing eukaryotic cells were selected during evolution because of the metabolic advantages they provided. Through endosymbiosis, mitochondria became the permanent guests of larger prokaryotic cells, leading to increased energy production. This evolutionary advantage allowed the mitochondria-containing eukaryotic cells to thrive.
Step-by-step explanation:
The early mitochondria-containing eukaryotic cells were selected during evolution because they provided a significant advantage to the organisms. The mitochondria, which were once free-living organisms, became permanent guests inside larger prokaryotic cells through a process called endosymbiosis. This symbiotic relationship allowed the host cells to obtain extra energy from the mitochondria, leading to increased metabolic efficiency. Over time, this advantage allowed the mitochondria-containing eukaryotic cells to thrive and diversify.