For all appearances, this looks like the skull of any human child. But there are two very special things about it. The first is that its owner was clearly deformed; its asymmetrical skull is a sign of a medical condition called craniosynostosis
that’s associated with mental retardation. The second is that the skull is about half a million years old. It belonged to a child who lived in the Middle Pleistocene period.
The skull was uncovered in Atapuerca, Spain by Ana Gracia, who has named it Cranium 14. It’s a small specimen but it contains enough evidence to suggest that the deformity was present from birth and that the child was about 5-8 years old. The remains of 28 other humans have been recovered from the same site and none of them had any signs of deformity.
These facts strongly suggest that prehistoric humans cared for children with physical and mental deformities that would almost have certainly prevented them from caring for themselves. Without such assistance, it’s unlikely that the child would have survived that long.
For any animal, it pays to be able to spot other animals in order to find mates and companions and to avoid predators. Fortunately, many animals move in a distinct way, combining great flexibility with the constraints of a rigid skeleton – that sets them apart from inanimate objects like speeding trains or flying balls. The ability to detect this “biological motion” is incredibly important. Chicks have it. Cats have it. Even two-day-old babies have it. But autistic children do not.
Ami Klim from Yale has found that two-year-old children with autism lack normal preferences for natural movements. This difference could explain many of the problems that they face in interacting with other people because the ability to perceive biological motion – from gestures to facial expressions – is very important for our social lives.
Indeed, the parts of the brain involved in spotting them overlap with those that are involved in understanding the expressions on people’s faces or noticing where they are looking. Even the sounds of human motion can activate parts of the brain that usually only fire in response to sights.
You can appreciate the importance of this “biological motion” by looking at “point-light” animations, where a few points of light placed at key joints can simulate a moving animal. Just fifteen dots can simulate a human walker. They can even depict someone male or female, happy or sad, nervous or relaxed. Movement is the key – any single frame looks like a random collection of dots but once they move in time, the brain amazingly extracts an image from them.
But Klim found that autistic children don’t have any inclination toward point-light animations depicting natural movement. Instead, they were attracted to those where sounds and movements were synchronised – a feature that normal children tend to ignore. Again, this may explain why autistic children tend to avoid looking at people’s eyes, preferring instead to focus on their mouths.
Alim created a series of point-light animations used the type of motion-capture technology used by special effects technicians and video game designers. He filmed adults playing children’s games like “peek-a-boo” and “pat-a-cake” and converted their bodies into mere spots of light. He then showed two animations side-by-side to 76 children, of whom 21 had autism, 16 were developing slowly but were not autistic, and 39 were developing normally.
Babies can say volume without saying a single word. They can wave good-bye, point at things to indicate an interest or shake their heads to mean “No”. These gestures may be very simple, but they are a sign of things to come. Year-old toddlers who use more gestures tend to have more expansive vocabularies several years later. And this link between early gesturing and future linguistic ability may partially explain by children from poorer families tend to have smaller vocabularies than those from richer ones.
Vocabulary size tallies strongly with a child’s academic success, so it’s striking that the lexical gap between rich and poor appears when children are still toddlers and can continue throughout their school life. What is it about a family’s socioeconomic status that so strongly affects their child’s linguistic fate at such an early age?
Obviously, spoken words are a factor. Affluent parents tend to spend more time talking to their kids and use more complicated sentences with a wider range of words. But Meredith Rowe and Susan Goldin-Meadow from the University of Chicago found that actions count too.
Children gesture before they learn to speak and previous studies have shown that even among children with similar spoken skills, those who gesture more frequently during early life tend to know more words later on. Rowe and Goldin-Meadow have shown that differences in gesturing can partly explain the social gradient in vocabulary size.
A child in the womb is not just some hapless creature waiting to be born into a world of experience. It is preparing. Through its mother, it senses the conditions of the world outside and its body plans its growth accordingly.
There is strong evidence that people who are under-nourished as embryos grow up to have higher risks of heart disease and other chronic illnesses. For example, people born to women during the Dutch Famine of 1945 had higher risks of coronary heart disease as adults.
We might nod our heads at this as if it were expected news, but it’s actually quite a strange result. After all, during the early stages of pregnancy, the embryo is actually relatively undemanding. Any embryos that get off to an early slow start can easily catch up during the foetal stage, and they can certainly do it after birth. But Jane Cleal and colleagues from the University of Southampton have found, from studying sheep, that catching up may actually be the problem.
You could argue that life is all about cheating death and having enough sex to pass on your genes to the next generation, as many times as possible. From this dispassionate viewpoint, human reproduction is very perplexing for our reproductive potential has an early expiry date. At an average age of 38, women start becoming rapidly less fertile only to permanently lose the ability to have children some 10 years later during menopause.
From an evolutionary point of view, this decline is bizarre. Other long-lived animals stay fertile until close to the end of their lives, with elephants breeding until their 60s and the great whales doing so in their 90s. In comparison, a human woman is exceptional in losing her child-bearing potential years or decades before losing her life. Even in hunter-gatherer societies that lack our access to modern medicine and technology, women who pass through menopause can expect to live well into their sixties.
Now, a pair of scientists have proposed a new model to explain the origins of menopause. Michael Cant from the University of Exeter and Rufus Johnstone from the University of Cambridge suggest that the loss of fertility helps to lessen reproductive conflicts between successive generations of women.
A few theories have already been put forward to resolve this conundrum. I’ve previously blogged about one of these, which suggests that the menopause reduces the health risks that repeated childbirth brings to both mother and child. This idea complements the most popular theory, known as the “grandmother hypothesis“, which suggests that older, infertile women can still boost their reproductive legacy by feeding, teaching and caring for their existing children and grandchildren.
The basic idea makes sense and while some studies have backed it up, it’s clearly not the whole story. Some analyses of hunter-gatherer populations have found that the indirect advantages of helping your family don’t outweigh the potential benefits of having more children yourself. Alone, the grandmother hypothesis can explain why women continue to live past the menopause, but not why they go through it in the first place.