How does natural selection lead to evolution? a. every generation is a new species
b. small changes add up over time
c. the fittest organism cannot reproduce
d. new species learned the behavior of old species

The answer to your question would be B:Small changes add up over time

Hope this helped

Aaron

B. Small changes add up over time

Explanation:

Evolution is a pretty slow process.  Each successful member of a new generation receives small changes in their DNA that helped them to survive, whether it's an existing trait that happened to be more helpful or a mutation.  Over time, these helpful traits gradually add up.  Eventually, the original species has been completely replaced by a new, improved version, that can look significantly (take horses for example, the very first horses were about the size of rabbits and had individual toes instead of hooves.  Over time, more beneficial traits added up, and the result is the horse we know today.)  While the traits of the original species might have been the most beneficial to them, as environments and other factors change, the species must change with it to survive.  You could compare this to computers.  The update you downloaded today might be the best thing to protect your computer now, but that same update won't be nearly as effective a year from now.  

I hope this helps!