A big brain is useless without the protection and education provided by an extended, nurturing parental presence, according to a new study comparing the lengthy childhoods of humans and certain brainy birds.
The average adult human’s brain accounts for about two percent of their body weight, but consumes 20 percent of the calories burned by its owner. In childhood the brain’s caloric demands are even greater, peaking at 43 percent of kids’ daily energy requirements.
“Brains are weird adaptations—they come empty and are very costly,” Michael Griesser, an evolutionary biologist from the University of Konstanz and co-author of the new research, tells Natalie Parletta of Cosmos. “So it takes individuals a lot of time to make this adaptation worthwhile.”
Studies of people and primates suggest that extended parenting is key to making the brain’s metabolic costs worthwhile and thus to the evolution of smarts more broadly, the researchers write. To paint a fuller picture of the role extended parenting plays in helping offspring survive and in the evolution of greater and more varied cognitive abilities the researchers looked to a more distant branch of the evolutionary tree: birds.
Corvid birds—a group including crows, ravens and jays—are noted brainiacs of the avian world and also spend extra time rearing their young. To systematically study where corvids’ stand relative to their feathered brethren, the researchers compiled a database of the life histories of thousands of bird species, including 127 corvids, reports Amanda Heidt for Science.
Compared to other birds, corvids spend more time in the nest before fledging, are doted on by their parents for longer and have larger brains relative to their bodies than other birds in the database, the researchers report this month in the journal Philosophical Transactions of the Royal Society B.
The study also included extensive field observations of two corvid species: New Caledonian crows and Siberian jays. The jays that watched their parents solve experimental puzzles learned faster and also received more food from their parents, per Cosmos. For the young jays, hanging around their folks made them more likely to survive and pass on their genes to offspring of their own, according to a statement.
These jays stay in family groups for as long as four years. In contrast, a group of chicken-like birds called megapodes don’t even incubate their eggs, which they lay in burrows or inside piles of decaying leaves. Megapode young begin life by digging their way through several feet of rotting plant material or soil and emerge able to fly and fend for themselves.
While observing the New Caledonian crows, the researchers saw parents who were tolerant of their offspring’s meddling as the adults were trying to use sticks to gather food. Tolerant parents are essential for the mischievous youngsters, which take up to a year to grasp valuable and complex life skills and stay with their parents for up to three years, according to the study.
“Both humans and corvids spend their youth learning vital skills, surrounded by tolerant adults which support their long learning process,” says Natalie Uomini, a researcher studying the evolution of cognition from the Max Planck Institute and the study’s lead author, in the statement.
“Moreover, corvids and humans have the ability for lifelong learning—a flexible kind of intelligence which allows individuals to adapt to changing environments throughout their lifetime.”
The researchers argue that the development of extended parenting is “pivotal” in the evolution of increasingly advanced cognitive abilities, a subject of intense debate. They write that, “extended parenting provides a safe haven, access to tolerant role models, reliable learning opportunities and food,” which makes offspring more likely to survive.
This pushes evolution in two ways. First, if the offspring of long-suffering, devoted parents live longer and have more babies, those traits may become more common through natural selection. Second, it also creates a situation that might allow uncommonly smart offspring to thrive, pushing forward the evolution of new cognitive skill-sets that take months or years to develop.
Uomini tells Science that studies into the development of other animals, even ones as different from us as birds, can grant humans “insights into the evolutionary conditions that helped our big brains and our intelligence to evolve.”