• 13th-century Italian philosopher St Thomas Aquinas believed that

13th-century Italian philosopher St Thomas Aquinas believed that all creatures and plants possess souls. • 17th-century French philosopher, mathematician and devout Catholic Rene Descartes believed humans to be set apart from the rest of creation. He viewed animals as unthinking machines, lacking conscious perception, but with God-given instinct. • 17th-century English philosopher and scientist John Locke held the opinion that animals have perception, memory and reason but not the ability for abstract thought. • George Romanes, a disciple of Darwin, wrote “Animal Intelligence” in 1882, the first attempt at scientific analysis of animal intelligence. He defined intelligence as “the capacity to adjust behavior in accordance with changing conditions.” • 20th-century Russian biologist