At the latest count,there have been twenty-seven separate hominin species. All of them are extinct — except us.
There are many hummingbird species, many antelope species, many large cat species. Why is there only one human species?
The answers to that question form the content of Chip Walter’s excellent new book, Last Ape Standing: The Seven-Million-Year Story of How We Survived and Why.
Last Ape Standing is rigourously up-to-date, full of the latest information and the newest theories about the evolution of modern humans. Walter goes a long way toward answering the question not only of our survival but also of our solitary survival.
What made homo sapiens the one survivor among all of those hominin species? The answers to this question give Last Ape Standing most of its freshness and interest.
Walter gives a number of answers, but his central theme is that we have survived because our brains are special, and our brains are special because we are neonates.
As the human brain evolved, it grew larger and larger. How was the typical female supposed to deliver a baby with such a disproportionately large head? The solution selected by evolution was to have human babies born before they were fully developed. No other mammal species delivers offspring that are as helpless — and helpless for so long — as are human babies.
Early birth would have seriously complicated life on the savanna. The advantages of early birth had to have been pretty significant to justify the increased stresses on time, resources, and safety.
If shortening the time between being born and bearing as many offspring as often as possible works so well for other mammals, for what reasons would evolution twist itself backward with Africa’s struggling troops of savanna apes?
The core of the answer lies in the human brain. It’s because of our large brains that we are born so early, and it’s our large brains that gave us a crucial survival edge.
Walter explains that we are born with “incomplete” brains. We spend the first few years of our lives completing the development of our brains. An infant’s brain consumes up to 85% of the energy the baby takes in each day. The brain of a three-year-old child is twice as active as an adult’s brain. A baby’s first priority is to grow brain connections.
As Walter notes, “You will have realized by now that this pretty much renders the old nature-versus-nurture debate irrelevant. The trillions of connections our brains make in childhood help explain why we are neither purely a product of our genes nor altogether the result of our personal experience, but both.”
Walter’s summary explanation of how this works is worth an extended quotation:
Your genes write the basic blueprint of what is personally possible, or impossible. They set the boundaries of who you are physically, psychologically, socially, and intellectually, but your epigenome etches the finer details of your personality—the ways you handle others, your fears, joys, risk for mental illness, your intellectual and emotional prowess, personal talents, confidence, proclivities for optimism or pessimism, and your annoying (not to mention altogether charming) quirks. They influence whether, when, and how your personal set of genes build the capacity for thought, emotional control, and a whole bushel of other future skills. Exactly what route the timing and depth of their effect takes depends on the infinitely complex molecular interactions that constitute your world and your “self.” No matter what, the result is that you come out of it all as unique as a snowflake.
We neonates aren’t just born early; we stay young far longer than do the offspring of other mammals, including other primates. The early plasticity of our brains never really stops, and it’s this flexibility that makes human mental activity unique. To a significant extent, we keep our curiosity and our mental agility throughout our lives. In this way, Walter argues, we remain “children” all our lives. We even look like children, with flat faces, big eyes, and all the rest of the physical features that make young apes, but not adults, look so much like us.
The crucial element of our neoteny is that “the longer a childhood lasts, the more individualized the creatures that experience it become.” Some animals are born with most of their behaviours hard-wired into them. We don’t think of individual insects or rabbits as being creative or curious or flexible. But our early birth and unending “childhood” makes us uniquely able to adapt, to learn, and to influence our surroundings.
Why do we need all of this flexibility? Walter argues that it’s because we are so social. “[W]hen our earliest human ancestors found themselves stranded on Africa’s expanding savannas, they were already inveterately communal.”
As our ancestors found themselves stranded on Africa’s expanding savannas, the ties that bound them would have grown tighter than ever.
On the savanna there were more predators, but fewer places to hide, less food, less water, than the jungle provided, even more competition from other troops given the dearth of resources in their new home.
Now add to all of this the pressures early-born children brought to the mix. You find yourself awakening every day working with your fellow creatures to survive, raising children, forging friendships, alliances, foraging and communicating as much as your brain and body will allow. You have no other choice because if you don’t, you will die.
So we survived, when all of the others didn’t. Our lifelong childhood saved us. And in the book’s last sections Walter argues that it’s only that mental agility, that creativity and curiosity, that will keep us here. We have unique brains, and we’ll need them if we’re to meet the challenges ahead.
Last Ape Standing is an engrossing book, one that I enjoyed as much as I have any non-fiction book I’ve read in recent months.