Imperfect copies as driver of evolution

Evolution is dependent on imperfect copies. If we had perfect reproduction, it would never evolve.

Imperfect copy

Term imperfect copy means that genetic information (DNA) from parent and offspring is not the same. These differences could be introduced in a process of making a copy of genetic information or there were some changes introduced during life of organism, before reproduction.

Evolvable programs

Speaking in programming terms (we can look at genetic information as program for creating an organism), we can have a program, that is able to copy itself and makes some small changes to own code while doing so. If we had a program that always copy itself perfectly, we would still have the same program, even if it runs for millions of years.

But if program would be able to randomly change small part of itself, there would be evolution. Wast majority of new programs would die (they wouldn’t be able to run), but some would survive and exist on their own and will create their own copies (containing changes they inherited and introducing their own changes in their offspring).

Resources of a computer are limited, so only the best programs would be able to run (and reproduce itself) and not so good programs would die. After some time, changes in code would accumulate in some instance of program and it might start doing something quite different from function of original parent program.

Personal note:

To see evolution in action, check some implementation of Richard Dawkins’s biomorphs.

It is simplified version of organism encoded in programming terms. This biomorph (organism) has 9 genes - variables influencing its width, height and branching depth. These 9 genes can be used to generate more than 118 billion different biomorphs. Humans, for comparison, have about 20,000 to 25,000 protein-coding genes.

You start with parent with some random values of genes. The children’s genes are identical to its parent’s genes except for a single mutation which changes its appearance slightly. You can select which child you want to become the parent in the next generation by clicking on it. By repeating this process, you can see how the biomorphs evolve over time.

Speeding up evolution

Since evolution is dependent on imperfect copies, a way to speed up this process is to use radiation. Radiation is known to disrupt genetic information - introduce mutations in DNA. If we would like to test many different mutations on a plant, we can take a bunch of seeds and irradiate them. Then can grow all of these seed and see if we introduced some beneficial changes (e.g. that plant will grow faster.) This is a way how GMO was done 30 years ago.

Imperfect copies in multicellular organisms

Single-cell organisms can create a copy of themselves to produce an offspring. But with multicellular organisms, it is more complicated. They are creating copies of their cells during whole life as part of growth and repair - new cells are still part of the same organisms.

In broad terms, genetic information (DNA) of an organism doesn’t change. Organism starts from one cell with some DNA and during development and whole life of organism, all cells have the same copy of DNA.

In closer look, there are many mechanisms, how is DNA in cells changed during lifetime:

  • every cell goes trough different effects from the environment (for example radiation),
  • every time DNA is copied, there is a chance of introducing a mistake in a copy,
  • every time DNA breaks (because of some physical tension, or some chemical that breaks it) there is a chance of mistake in repair,
  • there are viruses that can get into cell and put their DNA into DNA of cell,
  • there are parts of DNA that can be copied out and pasted to different part of DNA, by themselves (called transposable elements), …

Genetic information (DNA) of a single organism will not drastically change within lifetime of one organism. Every cell can have some small changes, but in broad view we can say, that one part of an organism has the same DNA as any other part of this organism. Different function of cell is not because of different DNA in them, but it is due to regulation on top of DNA.

Harmful changes

Process of introducing changes to DNA during lifespan is connected with cancer. There are some cells in our body that accumulate enough of these changes in wrong places and then program of extreme proliferation is triggered (they grow, make many copies and they don’t die). They do not follow plan of organism as whole, but they proliferate on their own without following the rules of survival of organism.

Normal cells (healthy cells without cancer) have processes of quality control. Once genetic material in a normal cell changes too much so that cell is in danger of not functioning properly, they have a way to commit a suicide. For example, our skin does this all the time. Skin is the first line of defence for many things (like radiation from sun, chemicals, etc.) so skin cells are programmed in a way that they die fast and are replaced by cells from below.