Determining whether life would have developed the same way on an Earth-sized planet in the same orbit on the opposite side of the Sun is purely speculative, as it involves a multitude of complex factors and variables.
The development of life on a planet depends on a wide range of conditions, including its atmospheric composition, geological activity, availability of liquid water, presence of organic compounds, and a stable environment over long periods. Even with similar initial conditions, small differences in any of these factors could lead to significant variations in the evolution of life.
While the same orbit and distance from the Sun might provide similar solar energy, the planet's specific characteristics would likely diverge due to a variety of factors, including geological processes, plate tectonics, and the interplay of the planet's atmosphere with the Sun and other celestial bodies. These factors can influence the planet's climate, the distribution of land and water, and the availability of necessary elements and compounds for life.
Moreover, the development of life involves a complex interplay of chance events, such as the occurrence of specific chemical reactions, the formation of self-replicating molecules, and the emergence of favorable evolutionary pathways. These chance events are influenced by countless variables and are difficult to predict or replicate.
Therefore, it is highly unlikely that an Earth-sized planet in the same orbit on the opposite side of the Sun would have developed life in exactly the same way. While there might be some similarities due to the shared solar energy, the specific evolutionary trajectory and the emergence of life would likely be unique to each planet.