When species are extensively hunted, individuals that reach reproductive maturity early make up a larger proportion of the population, because they have a better chance of reproducing  When species face diminished food resources, on the other hand, individuals tend to take longer to reach reproductive maturity
These considerations may help settle whether the primary cause of the gradual disappearance of North America' s mastodons, prehistoric animals related to elephants, was diminished food resources or human hunting, since
the average age at which mastodons reached reproductive maturity can be established from mastodon tusks, of which there are many fossils dating from different periods