Click on the button below to see data on the first occurrences of different ocean-dwelling organisms.
Notice that the first three graphs deal with the same group of organisms over different time periods, and the last three graphs deal with different groups of organisms over the same time period. Also, notice that, for the first three graphs, we can only see if the first occurrences happened within or outside of the tropics. For the last three graphs, we can see at exactly which latitudes the first occurrences happened. Don’t forget that the tropical regions are those with latitudes close to zero!
A. Based on the evidence presented above, do you think that the tropics are a cradle for diversity — in other words, is our hypothesis about diversification rates being higher in the tropics accurate? Explain how the data above support your thinking.
B. What sort of evidence would it take for you to change your mind about this?