Hypothesis - What are we even doing here?

Starting an experiment, there is always a question being asked- 

Does this mean that? Does this cause this?

A hypothesis is the basis of every experiment - you need this before going anywhere else. It is typically what the scientist(s) think the answer to the question is, and there are some variables to this word.

You might come across words like Null Hypothesis, which means scientists presume the answer to the question is no, there is no relationship between X and Y, this does not mean that, etc.

Here are some papers and what their actual hypothesis are;

PKD1 Promotes Functional Synapse Formation Coordinated with N-Cadherin in Hippocampus

Describes the importance of synapse formation for brain function - A synapse is the tiny gap between two nerve cells (neurons) passing signals to each other using chemicals or electricity.
Highlights the role of cell adhesion molecules in synapse formation. - These are proteins on the surface of cells that help them "stick" to each other.  Think velcro, but for cells.
It mentions previous studies on N-cadherin and PKD1. This is the wall we discussed in how to read a scientific paper. They need to lay the foundation before getting into their theory.  N-cadherin is a type of cell adhesion molecule found in the brain, and PKD1 is a type of enzyme, a protein that speeds up chemical reactions inside cells. 

Hypothesis - PKD1 might regulate N-cadherin in the nervous system

The Expensive Tissue Hypothesis 

This theory is centred around evolution, specifically how humans managed to develop their brain size without going crazy with their overall metabolic rate (This is the combined rate of every single chemical reaction happening in your body at any one time. There's a lot.) 

Hypothesis: Humans evolved a less complex gut and developed an easy-to-digest diet, leading to fewer energy-taxing organs and leaving more calories free for brain development.