In the early days of PCR, graduate students manually cycled samples between different temperatures using ice buckets, heating blocks, and water baths to amplify DNA.

“in the very early days we didn't have machines that would cycle between these three different temperatures or go through 30 uh different cycles of this so you can imagine uh the cheapest labor is a graduate student so you'd have an ice bucket you'd have a heating block and you'd have a you know sort of a a bath a water bath in terms of a different temperature with a timer in which you'd be literally moving samples and you'd be essentially a robot being able to do this”