Uwe Brauer <oub@mat.ucm.es> writes:

>> I guess you want gnus-thread-sort-by-most-recent-date and
>> gnus-article-sort-by-most-recent-date because gnus-thread-sort-by-date
>> sorts by the date of the root article.
>
> This is what I thought, but then the summary buffer displays the most
> recent dates first and the beginning of the buffer, which is not what I
> want as in 
>
> @ Start of buffer
> ...
> So this is not what I want:
> I want the most recent message at the end of the buffer not at the
> beginning

Then negate the sorting functions:

--8<---------------cut here---------------start------------->8---
gnus-thread-sort-functions is a variable defined in ‘gnus-sum.el’.

...

Documentation:
...

Each list item can also be a list ‘(not F)’ where F is a
function; this specifies reversed sort order.
--8<---------------cut here---------------end--------------->8---

BTW, there's also gnus-subthread-sort-functions which would allow you
to, e.g., have threads with the newest articles on top while still have
subthreads sorted chronologically from top (older) to bottom (newer).

Bye,
Tassilo