I'm assuming the contracts were all written up by a competent lawyer, once, and then just had the titles and salaries slightly changed from person-to-person.

Interviews were handled by the team that the new hire would be joining, and most personnel issues were handled locally too. Very rarely they'd be kicked up the chain to the department head, but honestly these issues were very rare.

Seriously, without an "HR police" to complain to, most people would just deal with interpersonal issues like adults and move on.

Who handles the sexual harassment complaints and the illegal hiring discrimination?

Who handles health insurance and 401k match?

I think the GP is from Australia, where a lot of that stuff is handled by government departments and labour laws. We have lots of labour protection laws that as an employee you can action through the Ombudsman, a federal department. The "401k" is called super anuation and is handled as a standardized legal requirement by the federal government, which simplifies it a lot. Because the ombudsman has teeth, they are pretty good at compelling businesses to comply with labour laws. Health care and so on are also all handled by the government or privately by the individual, rather than being tied to your company.

>Who handles health insurance and 401k match?

The Federal Government.

>Who handles the sexual harassment complaints and the illegal hiring discrimination?

Team leads, or lawyers if it gets far enough. You don't need a team of people on full-time for an event that happens twice a year.