Lorenz's research can be criticised for animal bias as it was conducted on goslings to investigate attachment. This is a potential problem as human attachment behaviour may be more complex than animal attachment behaviour as human emotions are more sophisticated towards their infants than birds. For example, human attachment is a two way process so it is not just the young who become attached to their mothers but also the mothers emotionally to infants. This makes it difficult to extrapolate the findings to humans, limiting the extent Lorenz's research can be used to explain human attachments.