Final answer:
Galaxies have evolved over time, growing in size through mergers and transforming in structure, with fewer individual galaxies present now compared to the past. Clusters and superclusters continue to form and grow as galaxies are drawn together gravitationally.
Step-by-step explanation:
Astronomers have gathered evidence to suggest that the properties of galaxies have evolved considerably over time. Originally, it was thought that galaxies appeared fully formed, but we now understand that they have grown in size and complexity through processes such as repeated mergers of smaller gas clouds. Observations reveal that early galaxies were smaller, more numerous, particularly less luminous gas-rich galaxies.
It is clear that mergers play a vital role in shaping galaxies, often resulting in changes in their structures. Collisions can result in spiral galaxies transforming into elliptical galaxies as they consume their gas and the rate of star formation declines. Over time, galaxies have grown larger as they have merged with one another while individual galaxies have become less numerous.
Additionally, galaxy clusters and superclusters formed from the gravitational attraction between galaxies, with observations supporting this continued growth. The large-scale structure of the universe, with its clusters, voids, and filaments, also indicate a dynamic and evolving cosmos.