The Birds & the Bees

How Honey Helped To Make Us Human

Most discussions of the evolution of the human diet implicate meat as the proverbial smoking gun responsible for many hallmarks of human evolution such as brain expansion, cooperation, family formation, pair bonding, tool making, and even selection of marriage partners,” says Dr Alyssa Crittenden, Lincy Assistant Professor of Anthropology (and honey enthusiast!), University of Nevada. “Some alternative interpretations discuss the importance of plant foods, like tubers (starchy underground storage organs – similar to potatoes), and suggest that the collection and consumption of plant foods is what made us human. The debate of the significance of meat versus potatoes, so to speak, appears to be rooted in deep evolutionary time. More recently, however, there has been a trend in incorporating a wider range of foods in evolutionary reconstructions of the human diet.

With the popularity of the Paleolithic Diet and caveman cooking steadily on the rise, it is increasingly important to turn to different lines of evidence to inform our thinking on the history of humans and their food. As new lines of evidence converge, it is becoming clear that the ancestral human diet was varied and included a combination of both animal protein and fat as well as plant foods; a Paleolithic menu that included meat, potatoes – and dessert!

It appears that the human sweet tooth has a long history in human evolution. New research proposes that honey may have been important in human evolution. Upper Paleolithic (8,000 – 40,000 years ago) rock art from all around the world depicts images of early humans collecting honey. The images range from figures climbing ladders to access hives residing high in trees to figures smoking out hives filled with honeycomb. Honey and bee larvae are important foods consumed by many populations of hunters and gatherers worldwide. Foragers in Latin America, Asia, Australia, and Africa include honey and bee larvae as major components of their diet.

The Hadza hunter-gatherers of Tanzania, the population with whom I work, even list honey as their number one preferred food item.

The Hadza consume honey and larvae of both stingless bees and stinging bees, including the African killer bee (Apis mellifera). The Hadza locate the hives with the assistance of a wild African bird, the aptly named honey guide (Indicator indicator). The honey guide bird and the Hadza honey hunter communicate back and forth through a series of whistles and the bird guides the honey hunter, tree by tree, to the bee hive. Once the honey hunter has located the hive, he pounds wooden pegs ito the trunk of the tree, climbs to the top where the hive is located, chops into the tree to expose the hive, and smokes it out by placing burning brush into the opening. Smoking the hive acts to pacify the bees by dulling the senses of the guard bees who protect the opening of the hive. The bees see the smoke as a habitat threat and focus on collecting enough honey to rebuild their hive elsewhere. This allows the hunter to collect the honeycomb without being stung by the killer bees. The honey guide bird patiently waits outside of the hive and as the honey hunter obtains his honeycomb prize, the honey guide bird is rewarded with its delicious prize – wax from the comb and bees.

Honey is a highly nutritious (and delicious!) food source, composed primarily of fructose and glucose. Combined with larvae, which is high in protein, fat, and B vitamins, honeycomb is nature’s energy bar. The ethnographic cross-cultural evidence of honey consumption, combined with depictions of honey hunting portrayed in rock art around the world, suggest that honey has long been been a part of human history. Early humans, and their expanding brains, would have greatly benefited from consuming honey and bee larvae because the human brain needs glucose to fuel the high metabolic demands of neural development and function. The Paleolithic diet likely included meat, plant foods, and honeycomb – one of the sweet secrets to human evolution!

Energy To Burn

Hummingbirds require an incredible amount of energy to flap their wings 50 times or more per second in order to maintain hovering flight. In fact, if a hummingbird were the size of a human, it would consume energy at a rate more than 10 times that of an Olympic marathon runner. They power all of their energetic hovering flight by burning the sugar contained in the floral nectar of their diet. Research from the University of Toronto Scarborough published in Functional Ecology shows they are equally adept at burning both glucose and fructose; a unique trait other vertebrates cannot achieve.

"Hummingbirds have an optimal fuel-use strategy that powers their high-energy lifestyle, maximizes fat storage, and minimizes unnecessary weight gain all at the same time," says Kenneth Welch, assistant professor of biological sciences at UTSC. What's very surprising is that unlike mammals such as humans, who can't rely on fructose to power much of their exercise metabolism, hummingbirds use it very well. In fact, they are very happy using it and can use it just as well as glucose.”

Hummingbirds are not fooled by the sugar substitute that sweetens most diet cola. And they certainly aren’t keen on plain water. It takes only three licks of their forked, tube-like tongues to reject water when they expect nectar. They pull their beaks back, shake their heads and spit out the tasteless liquid. The birds' preference for sweetness is plain. Now scientists can explain the complex biology behind their taste for sugar.

In a paper published in Science, scientists show how hummingbirds detect sugars using a transformed taste receptor – one that detects the savory umami taste in all other vertebrates. This modification helped hummingbirds to sense nectar, a change that allowed them to exploit a distinct environmental niche compared to other birds. Feasting on nectar and the occasional insect, the tiny birds expanded throughout North and South America, numbering more than 300 species over the 40 to 72 million years since they branched off from their closest relative, the swift.

In vertebrates, responses to sugars and amino acids, respectively, require distinct taste receptor molecules. The T1R2-T1R3 taste receptor detects sweet tastes (like the sugars in plant-based carbohydrates), and the T1R1-T1R3 variety detects savory or amino acid tastes (like those in meat). Along the way, birds, including the ancestors of hummingbirds, lost the gene that encodes T1R2, part of the sweet taste receptor. Thus, it might seem like birds should be blind to sweets, yet scientists know from watching hummingbirds flock to nectar that this is not true.

To explain the basis of this behavior, Maude Baldwin et al scanned whole-genome sequences of ten bird species, including hummingbirds, looking for genes encoding the non-sweet and sweet taste receptor components, respectively. As expected, they only found the former. To determine if the non-sweet taste receptor components in hummingbirds might have transformed to take over sugar sensitivity, Baldwin et al. expressed the non-sweet receptor components (T1R1-T1R3) of both chickens and hummingbirds in vitro and looked at their response to amino acids and sugars. While the chicken receptor only responded to amino acids, the hummingbird variety responded to sugars, too. The researchers propose the hummingbird T1R1-T1R3 adapted to regain the sweet taste perception lost in other birds. This allowed hummingbirds to feed on a resource not used by other avian species, the authors say, and to flourish.

“It’s a really nice example of how a species evolved at a molecular level to adopt a very complex phenotype,” said Stephen Liberles, HMS associate professor of cell biology. “A change in a single receptor can actually drive a change in behavior and, we propose, can contribute to species diversification.”