34) Speciation without geographic isolation is called speciation. 35) Organisms that possess more than two complete sets of chromosomes are said to be 36) In a hybrid zone,. can occur if the reproductive barrier between two species is weak, as seen among cichlids in the murky waters of modern Lake Victoria. 37) The fossil record shows that for many plant and animal groups, the time between speciation events averages what years? 38) The earliest discovered fossils are of dating back to years ago.