A recent study revealed that in the early Universe, there were far more peculiar galaxies, and now, there are far more spirals.1 (See Figure 1.) This means that peculiars are evolving into spirals. It seems likely that the peculiars first got organized into ellipticals. Then, the galactic forces continued to exaggerate the aspect ratios into lenticulars, and then finally into spirals. The fact that the number of ellipticals and lenticulars has stayed roughly the same further suggests that those are evolutionary stages in a process.
Figure 1. Distribution of galaxy types, 6 billion years ago versus now.


1. Delgado-Serrano, R. et al. (2010): How was the Hubble sequence 6 Gyr ago? Astronomy and Astrophysics, 509 (A78): 1-11

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