The environmental dependence of Type Ia supernova (SN Ia) luminosities is well-established, and efforts are being made to find its origin. Previous studies typically use the currently-observed status of the host galaxy. However, given the delay time between the birth of the progenitor star and the SN Ia explosion, the currently-observed status may differ from the birth environment of the SN Ia progenitor star. In this talk, I will present how to trace back the SN Ia progenitor star birth environment, employing the chemical evolution and accurately determined stellar population properties of host galaxies. Then, I will show you how the birth environment of the SN Ia progenitor star and currently-observed status of galaxies are different and they are sampled from different populations. Interestingly, we find that [α/Fe]_Birth clearly splits the SN Ia sample into two groups: SN Ia exploded in [α/Fe]_Birth-rich or [α/Fe]_Birth-poor environments. SNe Ia exploded in different [α/Fe]_Birth groups have different weighted-means of light-curve shape parameters: 0.81 ± 0.33 (2.5σ). They are thought to be drawn from different populations. Finally, an application of this work and future works are presented.