Seriously It's depend the spacey involve. Crocodile and shark as not evolve for millions of years. But whale have drastically change during the past millions years as the fossils told to the mass spectrometer who analyse the radioactive elements. You know human is a branch of monkey. At the beginning 4 millions years ago was the creation of and another monkey spacey who slowly became to walk to see above the plants. This evolution was made because a climate change cause the tree to die and you far ancestor needed to adapt to search food and see predator. One thing is sure, when a spacey is not constraint to survive in an another situation they have no evolution. Today we can see skin colour evolution to protect the cell by UV light. It's not only the brain can adapt but cell too. That why every live form on earth can adapt to a speed of change and then evolve.
In the book "the beak of the finch" the author studied finches on the galapagos islands. He found that if food was plentiful the very next year the finches would have smaller beaks. If food was scarce or it was dry the finch the next year would have larger beaks to crack the hard shells of their seeds. This shows that changes can occur within one generation.