I think you forgot to account for lifespan. Relatively long-lived mammals have a tendency to raise their offspring over many years (e.g. Orangutans 6-8 years, ~

I think you forgot to account for lifespan. Relatively long-lived mammals have a tendency to raise their offspring over many years (e.g. Orangutans 6-8 years, ~9 years for Elephants, etc.).