But the simple fact is that this has never been observed. And in fact the scale of change is vastly different. It's one thing, as Darwin did, seeing finches with different types of beak; it's a huge jump to say that the same mechanism could explain the appearance of a heart, the appearance of bone, the appearance of feathers, the appearance of warm-blooded creatures, etc. Big changes have never been observed, and it is not good scientific practice to extend known information far beyond what has been seen. So it is not scientific to use very minor changes as evidence to support the great changes required by the theory of evolution.

• The 'Big Bang' must remain an interesting theory, and cannot be regarded as a fact.
• Classification of animals tells us nothing about how they came into existence.
• Minor changes are not scientific evidence of large changes.

3. The cell

We want to think briefly about the cell, because it is the basic building block of life. All life consists of one or more of these building blocks. The simplest forms of life are single-celled creatures. By contrast, most forms of life consist of many cells. For example, the human body contains more than 10 million million cells of about 200 different types.

Scientists have discovered that there are many parts to a typical cell.

Just as a house has a kitchen, living room, bedroom and bathroom, so a cell has specialised areas partitioned off for separate uses. The diagram shows just a few of the specialised areas.

A room in a house is separated from the rest of the house by its walls, and then its door is used to control what comes in and out. In the same way, each compartment of the cell is sealed off from the rest of the cell by its own membrane, which has openings to allow some chemicals in and out and to prevent others passing through.

There are highly sophisticated systems to ensure that only the correct chemicals come in and out of compartments. In total there are more than twenty different sections in a cell, and these systems must accurately regulate chemical movements between every one of these sections.

One thing that it is important to remember is that every cell that has ever been discovered has all of these systems in place to enable it to survive.