theory 1

The ancestors of giraffes had short necks, and there was greatcompetition for the plant food near the ground. Some of thegiraffes kept trying to stretch their necks to reach leaves higherin the trees. As they stretched and stretched, their necks becamelonger. As their necks became longer, they were able to reach morefood. Those ancestral giraffes survived to reproduce, while thegiraffes that had not stretched their necks died. The offspring ofgiraffes with stretched necks inherited the longer necks. Thisprocess continued for generation after generation. In this way,giraffes evolved with longer and longer necks.

Theory 2

The ancestors of giraffes had short necks, and there was greatcompetition for the plant food near the ground. Some of theancestral giraffes naturally had slightly longer necks than others.The individuals with longer necks could reach leaves higher up intrees, and therefore could eat more food. Because those ancestralgiraffes ate more food, they survived to produce offspring whilethe individuals with shorter necks did not. The offspring ofgiraffes with longer necks inherited the longer necks. This processcontinued for generation after generation. In this way, giraffesevolved with longer and longer necks.

a. In Theory 1, what caused the giraffe neck to becomelonger?

b. In Theory 2, what caused the giraffe neck to becomelonger?

c. According to what scientists now know about genes, could thegiraffes’ offspring have inherited longer necks as described inTheory 1? Explain.

d. According to what scientists now know about genes, could thegiraffes’ offspring have inherited longer necks as described inTheory 2? Explain.

e. Which of the two theories matches Darwin’s theory ofevolution? Explain.