3. how does the consistency of the milk change during the production of yogurt? what facilitates this change?

The transformation of milk into yogurt is due to a fermentation process, mediated by two types of bacteria: Lactobacillus bulgaricus and Streptococcus thermophilus. Ideally yogurts should contain approximately equal amounts of these bacteria.

These bacterial microorganisms use lactose, milk sugar, as a source of carbon and energy through a process of lactic fermentation. This transformation results in the production of lactic acid, responsible for the acidic character of this food. The increase in lactic acid converts milk consistency into yogurt consistency. This process occurs when the temperature of the milk is around 40 ° C.  

This process is facilitated in situations of high temperature and absence of oxygen. Because the responsible bacteria are anaerobic beings.

the fossil record provides evidence of a common ancestor to many species.