Back then in the year of Aristotle's times the scientific method wasn't as up to date as it is now, But people had theory's and believed that non-living matter produced living things. They based everything on what they saw. Aristotle dissected animals and study behavior in their environment. Newer science researcher methods were learning more about nature and science.
There are 3 key methods to research and analyze data. Observation, Investigation, and finally experimentation.