In 1988, a biologist named Richard Lenski introduced 12 genetically identical populations of E. coli to test tubes and subjected them to the same conditions: a period of growth followed by starvation. After several years, all 12 strains had adapted to the conditions in similar ways; however, their genetic sequences were very different. Which of the following conclusions from this experiment is correct? a. The 12 E. coli populations underwent convergent evolution resulting from similar environmental conditions.
b. Similar selective pressures on genetically identical organisms can have different effects at the level of the genome.
c. Evolution by natural selection can be directly observed in organisms with short generation times.
d. Similar phenotypes may result from a variety of underlying genotypes.