Lamarckian theory explained giraffe neck evolution
by arguing that constant stretching slowly elongated their
necks, and that they then passed on these beneficial longer
necks to their offspring.8
The textbooks then explain that
we now know acquired characteristics are not inherited,
and conclude with Darwin’s explanation for how long
necks evolved—viz., normal variation of neck lengths exist
and evolution consistently selected for longer necks until
giraffes reached their modern height (as explained by Kottak,
quoted above). Giraffes with shorter necks were less
likely to get a good meal, while those with longer necks
were more likely to obtain one. As a result, giraffes with
longer necks thrived, while those with shorter necks were
more apt to become sick and die, or at the least produce
fewer offspring.3
Gould’s summary of the typical textbook
story is as follows: giraffes evolved ‘long necks in order
to browse the leaves at the tops of acacia trees, thereby
winning access to a steady source of food available to no
other mammal’.9