Is human longevity due to grandmothers or older fathers?

Why do humans tend to live such a long time? Our closest relatives, the chimpanzees, can last into their mid forties in the wild. Yet somewhere in the last six million years, human lifespans have lengthened dramatically, so that living into our seventies is no big surprise.

The last few weeks have seen some exciting new developments in this area. First, a recent paper featured in The Conversation showed that at all ages, humans are less likely to die than chimps.

Excitingly, however, modern health care, diets and the steady decline in violent deaths have slashed mortality rates of young adults. People in societies like Japan are now almost 200 times less likely to die in at a given age than people of the same age in hunter-gatherer societies.

The dramatic declines in modern mortality rates are almost entirely due to technological developments, but the lengthening of the maximum potential human lifespan since we diverged from the other great apes poses an intriguing evolutionary problem.

Our bodies only function as well as they do because we have a quiver-full of cellular repair and maintenance mechanisms. For example, we have systems that correct mistakes in DNA replication, and others that detect and kill off pre-cancerous clusters of cells.

But natural selection optimises those mechanisms to operate during our expected lifespan. Modern people who live beyond seventy are much more likely to suffer from cancers, dementia and other diseases of old age. Few of our ancestors – even the most recent ones – lived that long, and these late-onset diseases didn’t interfere with their successful reproduction. By the time they got the diseases, our ancestors had already passed their genes on – and that’s why we carry those same genes.

Six million years ago, the diseases of old age probably kicked in before our great-ape ancestors hit forty. The evolution of a longer lifespan involved a steady postponement of ageing. But only if older individuals contribute to the success of their own genes can this actually happen. Continue reading Is human longevity due to grandmothers or older fathers?

The Origins of Racism

Could the prejudice against Collingwood supporters come from the same evolved tendencies that sometimes give rise to racism and religious bigotry? Source: woowoowoo on Flickr

A criticism often flung at evolutionary studies of human behaviour is that, in revealing the origins of the human psyche’s darkest aspects, they might substantiate our worst traits. The hysteria over sociobiology arose from concerns that a biological understanding of human behaviour and society would be used to justify racism, sexism and various other forms of prejudice.

Ideologues will usually grab at anything that suits their world-view and ignore whatever contradicts it. But that should not change the questions scientists ask. In fact modern evolutionary biology is making enormous contributions to our understanding of how our ideas of race, racism, gender and sexism arise.

In this vein, I have enjoyed catching up with some of the most recent research on the evolution and neurobiology of race and racism. Two of the most interesting reads are an article on the Roots of Racism by Elizabeth Culotta, and a Nature Neuroscience review by Jennifer Kubota and colleagues on the Neuroscience of Race.

Where does racism come from?

Culotta’s article, part of a special section in Science on Human Conflict, isolates two important themes that are gathering support. First, racism is one of many expressions of our evolved capacity to live and work in groups. The very human tendency to identify with an “us” defines the broader “them”.

Outgroup “hate”, then, is a mirror image of ingroup “love”. Religious bigotry, ethnic mistrust and even an intense dislike of Collingwood supporters arise at first from our tendency to form coalitions and allegiances.

The other important theme is that antipathy toward members of other groups gains much of its traction through fear, particularly of males. The snap judgments people make about others may be part of a sensitive alarm system that evolved when the people most likely to present a violent threat were strange males.

This idea is part of a simmering discussion about the importance of male aggression in human evolution. According to the “Male Warrior Hypothesis”, men have evolved stronger tendencies to form coalitions to attack other groups and to defend their own groups, families and property against coalitions of other men. Continue reading The Origins of Racism