5.4 - Lamarkism/ Darwins theory of natural selection

What is Lamarkism? (inheritance of acquired characteristics

Lamarkism is the idea that if an organism acquires certain characteristiques while they are alive, that it could pass them onto its offspring.
For an example:
 Gertrude has been texting since she was very little. Years of texting on her blackberry have made her thumbs big and full of muscle and dexterity. As a direct result she has no problem opening hard to open jars, playing thumb war, and anything that might need a thumb to fully function. Her neighbor, Arthur thinks her thumbs are sexy, and mates with her. (refer to 5.5 to find out what mating is).  According to Lamarkism, the bigger/muscular thumb would pass onto her offspring because it was an acquired characteristic in her lifetime. 

What is Darwins theory of natural selection?

Natural selection, or otherwise known as Darwinism, is the theory of which if a certain acquired trait in a species genetic coding is highly effective in the specific environment in which the organism lives, it will most likely be passed onto it's offspring. Highly effective in areas like sexual reproduction and survival.
If a trait were beneficial it has good chances it would be passed on. If it had a negative effect (Like cause the organism to mate less) it would probably not be passed on. Traits that are neutral would most likely be passed on since it could be beneficial one day.