Reversing conversation order
Use Reverse Conversation Order to reply from the "top" of the stack inside Gmail.
If you choose, you can reverse the order that email gets "stacked" in your Gmail inbox. This means that in a back and forth email conversation, the newest email will be "on top" of the stack, and you will reply from the top. We believe that being able to reply without scrolling to the bottom is a big productivity boost! You can change this option in your Preferences.

Replying from the top in Gmail

Newest messages in the top in Gmail

Conversation Order in Preferences

Click the "Reverse Conversation Order in Gmail" preferences to enable this option.
Enable Reverse Conversation Order in your preferences