Question: Explain the theory of life

Tom Hartley answered on 16 Jun 2010:

This is a big ask, osama. I don’t think there is a “theory of life” but I will try to summarize the main ideas underlying modern biology, which are A) Evolution and B) Genetics.

1) Organisms such as plants and animals reproduce, with offspring that are similar to there parents because they inherit characteristics – we now know that this inheritance is due to genes which are passed from the parents to offspring.
2) Although offspring are similar to their parents they are not identical because i) mutations can change the genes and ii) for sexually reproducing organisms genes are inherited from both parents and mixed up in unpredictable ways.
3) This variation means that some organisms are better equipped to survive and reproduce than others (called adaptation).
4) More poorly adapted organisms die young, fail to reproduce, fail to nuture their young effectively or produce less young. They are at a disadvantage.
5) Over time, well adapted organisms prevail over poorly adapted ones, different organisms emerge -each suited to its particular environment and circumstances.

That is evolution in a nutshell.

6) Genes are encoded by a special chemical DNA which has a highly variable structure with elements (called base pairs) that can be swapped around in. The sequence of different base pairs forms the code (it has four “different” letters).
7) The code is used to describe the structure of proteins which perform different functions in the body, for example, one protein might be used to digest fat, another one is useful in receiving signals sent from one nerve cell to another. It’s quite a straightforward code which you could easily learn and begin to decode yourself. However the proteins themselves can be very complicated and there important properties come from their shape which is hard to predict from the code alone.
8 ) The proteins and the way they are expressed in different parts of the body (also controlled by genes) determine the shape and structure of the body from proteins to cells to organs.
9) by “selecting” genes that work best (as described in 1-5 above) the organism gradually gets better and better.

That is genetics in a nutshell (very simplified, because the mechanisms are rather interesting and complicated, and because I’ve forgotten most of it!).

Evolution is rather hard (not impossible) to study, but biologists and chemists already understand the biochemical mechanisms of genetics and metabolism in impressive detail – the key discoveries were made last century and progress has been incredibly rapid; one of the main achievements of 20th century science I’d say (together with Quantum Mechanics in Physics).