More evolution evidence... I think (Earth, experience, advent, deformities)

[Torgo]

I have a strong background in developmental biology, evolutionary biology, and genetics, and I hope I can contribute.

As for the kid, most gross body part duplications in humans (and animals outside the laboratory) are due to cell signaling mishaps in the early embryo rather than genetic changes. Cells signal each other and reinforce each other's messages until one focus of cell division/differentiation is set up, which grows into the arm/leg/spleen/whatever. Sometimes things just go wrong and you get two or more foci.

When I say entirely new I don't mean variations of functions like yet another camoflauge pattern, but a truly new property, like, say, a virus picking up a simple one-celled optical sensor or the start of a nerve ending or something. These things had to start somewhere according to evolution.

These things are far too complex to arise in one step. Even so, there is little if anything in biology which arose completely independant of any preexisting system or trait. I'll use the nervous system as an example. All living things pump ions across their cell membranes using ion channel proteins, generating an electrical charge. Just about all living things use this membrane charge as a major part of a system that pushes food molecules into the cell against the gradient. Different branches of life have done different things with this system, however. Chloroplasts and photosynthetic bacteria use the charge as part of their photosynthesis, and mitochondria use the charge as part of their energy generation apparatus. Infectious bacteria use their membrane charge to some degree to electrically repel white blood cells.
At some point, a "voltage gated" version of the ion channel evolved. These channels change the direction of ion pumping, or start or stop, depending on the amount of charge at their location. This allows waves of membrane charge to propogate across the cell membrane. These waves are used quite widely in cell signaling. One example is how egg cells use them to activate proteins which stop the entry of more than one sperm. In animals muscle cells take this a step further, and allow the waves to propogate from one cell to another and signal multiple cells to contract in unison. This is most important in the heart in humans, where it allows all the cells to beat in unison. Nerve cells are just another co-opting of the membrane charge system, in which cells become specialized specifically for the propogation of these ion waves and influencing the activity of other cells.

Sorry if my example got kind of long and technical, but it was the best example I could think of for the way nothing "entirely new" ever really develops in biology/evolution and how sometimes you need a lot of small additions to create a large one.