The majority of creatures on Earth are hungry most of the time, every single day. That’s true of almost all of them and some of us, too. A change by a degree or two in the temperature could mean a world of difference in how many creatures are able eat, us included. A brief passage from Daniel Lieberman’s excellent book, The Story Of The Human Body:

“Are you worried about rapid global climate change today? If not, you should be, because rising temperatures, altered rainfall pattern, and the ecological shifts they cause imperil our food supply. Yet, as we have already seen, global change has long been a major impetus in human evolution because of its effects on the age-old problem pf ‘what’s for dinner?’ It turns out that getting enough food in the face of global climate change also triggered the age of humans. 

Getting dinner (or, for that matter, breakfast and lunch) probably does not dominate your list of daily concerns, yet most creatures are almost always hungry and preoccupied with the quest for calories and nutrients. To be sure, animals also need to find mates and avoid being eaten, but the struggle for existence is often a struggle for food, and until recently the vast majority of humans were no exception to this rule. Consider also that acquiring food is even more taxing when when your habitat alters dramatically, causing the foods you normally eat to vanish or become less common.”