Are cell mutations troublesome?
A mutation is a change in the genetic material of an organism. We’re made from
trillions of cells, each with a nucleus composed of DNA – a set of instructions that
tells the cell what to do. Cells copy themselves with astonishing accuracy, but every
now and then a piece of code is copied incorrectly. This is largely due to natural
radiation interacting with our DNA. This incorrect piece of code can become a
permanent change in the DNA. Mutations are rarely harmful though. Indeed, most
mutations go unnoticed, as the body has mechanisms to stop a cell copying itself.
Sometimes mutations can benefit organisms. When a mutation allows an organism
to cope better with an environmental stress, it will be passed on to future generations
through natural selection.
Evolution works through mutation. Mutation is the source of all new genes and
subsequently all new traits; evolution is the process by which the gene pool changes
as a result of natural selection. The reason there is variation for natural selection to
"select" from is that there are mutations producing new genes and new traits.
The eye is a famous example of an organ that had to evolve through many, many
steps of mutation. Scientists think the eye probably started out as just a spot of light-
sensitive pigment; then at some point it was formed into a cup, a lens formed over
the mouth of that cup, etc., and eventually we ended up with they types of eyes we
have today. Interestingly, eyes have developed two separate ways on Earth: the
compound eyes of insects function on fundamentally different principles than the
single gelatinous eyes of vertebrates.
It is true that mutations are almost always damaging. This is because genes and
their protein products are so complicated; if you change something randomly, it will
very likely stop the gene or protein from working right. But, rarely, a random change
will actually -improve- the functioning of the gene or protein product. Then, instead of
being eliminated from the gene pool because it causes death or disease, the gene's
carrier survives and the gene spreads throughout the gene pool over many
generations. Many of these small, beneficial mutations accumulate over millions of
years to produce whole new species.