
Originally Posted by
kuronosan
You're confusing development with growth, Plow. Development is when cells divide until they reach a stage where mitosis/meiosis is no longer used to differentiate cells. Growth would be the constant replacement of red blood cells or bone tissue. Your red cells develop from a stem cell into a red blood cell, they don't grow - yes. A human being, however, while they can develop into an adult, do not 'develop' into adults on a cellular level. Their cells divide and facilitate growth.
Degenerative disorders such as Alzheimer's use your own body's degenerative capabilities (similar to how your body breaks down bone to remake bone) in order to cause this to happen. So yes, you are correct. This same process is a little different in muscle. Your body doesn't break down muscle to make new muscle. Exercise or atrophy breaks down muscle and it is only replaced when the body has a reason to replace it.
But here again, Plow - you don't 'develop' new muscle. You grow new muscle. Muscle cells may develop, but in the general term of development used in relation to a developing organism you are not developing muscle. You are replacing it. The body can only work so fast with the amount of nutrients, enzymes, and cells it contains. The reason why degenerative disorders such as Alzheimer's are so dangerous is because they often break down tissues that cannot be replaced. Liver tissue regenerates. Nerve tissue does not.
In terms of an organism, it has finished developing. If you're talking about human development using a broad term, then you are correct. Human beings never stop developing. If you're talking about humans in terms of the organism made up of cells, they stop 'development' once they become a fetus and from then on out the body is simply growing and reacting normally.
Why else do you think puberty takes so long to onset? It's not because it's a magic time and the body feels right. Social and chemical changes (and even genetic factors) determine when the body is ready to release sufficient levels of hormones to start. Puberty is starting at a younger age these days because of many factors.
I dunno how else to put it. Women develop breasts, but in terms of development the breasts are always there, they just haven't grown yet.