Hi hope you can help me.

Im learning statistics at uni. They tell me a null hypothesis is neutral between groups, and an alternative hypothesis will be bias. For example:
Null hypothesis (ho) fat and skinny girls give equally good blowjobs.
Alternative hypothesis (ha) fat girls give better blowjobs than skinny girls.

But say a ton of research has been done, proving fat girls give better blowjobs than skinny girls.

Could the null hypothesis be, fat girls give better blowjobs than skinny girls
And the alternative hypothesis be, skinny girls give better blowjobs than fat girls.

If this is true, it contradicts my uni teachings that all null hypothesis are neutral between groups.