Harry Harlow performed an experiment in which infant monkeys were housed with two artificial "mothers": one that was made of cold mesh and provided food, and one that was made of cozy cloth but didn't provide food. Harlow found that the monkey infants:

Whenever diploid populations are in hardy-weinberg equilibrium at a particular locus a) the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change. b) natural selection, gene flow, and genetic drift are acting equally to change an allele's frequency. c) this means that, at this locus, two alleles are present in equal proportions. d) the population itself is not evolving, but individuals within the population may be evolving.