Chromosome breakpoints contribute to genetic variation.

In chapters 6 and 7 of NOT A CHIMP I explain how large structural upheavals in the genome, involving segmental duplication of large sections of DNA, inversions, and deletions, can lead to novel sources of genetic variation because they can either produce a new family of genes, or dupes, upon which natural selection can differentially act, or because they disrupt genes or families of genes when chromosomal breakpoints occur within genes or close by. Now a team led by Harris Lewin, of the University of Illinois, has shown that such chromosome breaks do not occur randomly, invariably occur in gene-rich parts of chromosomes, as opposed to genetic deserts, and in areas abounding in copy number variants of genes, insertions and deletions. Furthermore, different classes of genes are associated with breakage-susceptible to breakage-resistant parts of chromosomes, the former over-represented with genes for immune system and muscle contraction, for instance. Yet more evidence that structural tectonics in the genome are, if anything, more important than prosaic point mutations in the genetic code in providing raw material for natural selection to operate on.

Ape behaviour reveals secrets of human evolution

Nice article from Dan Jones, mainly about how Robin Dunbar and various colleagues are investigating the affects on primate group size of climate and thus food availability, to get an ecological handle on human evolution. Raises interesting questions: as you move from chimps to Australopithecenes, brain/cranium size increases, suggesting larger social groups. But how did Australopiths eke out a sufficient existence to support larger groups and bigger brains? Did they roam more, temporarily fission into small groups, or (very unlikely) eat meat?

The article also goes on to look at how sexual dimorphism reduces from chimps to Homo erectus and man, suggesting a trajectory toward monogamy. How was female behaviour changing, and what had that to do with food availability? Jones also reports on work by Karen Isler and Carel van Schaik who plotted brain size against fecundity for over 1200 animal species. Normally, when brain size increases fecundity goes down, because of the inordinate investment in grey matter, but humans have the biggest brains of all animals and much higher fecundity than the great apes and earlier hominins. The answer? Allometernal care - helpers at the nest. It works for big-brained birds too. For primates, including us, they calculated the magic number for brain size at which reproductive effort will be compromised if step-mothers don't kick in - one litre!

How our brains process admiration and compassion

When we feel admiration for the Mother Theresas of this world, or compassion for someone in great emotional or physical pain, we draw quite literally on gut feelings. As this paper by Hannah and Antonio Damasio, and others, shows, these sort of social stimuli are registered in the anterior insula, anterior cingulate cortex, and precuneus - all parts of the brain dubbed "the social brain". The insula, in particular, is the place where gut feelings of pain, disgust etc. are translated into much higher-order social intelligence because nerve impulses from our viscera - visceral sensations - excited by external stimuli (called interoception), pass to the insula and cingulate and then on to prefrontal cortex where they are translated into appropriate emotional responses. See chapter 10 of NOT A CHIMP for more detail. Many of these areas have evolved uniquely in size or internal structure in humans.

What makes us human?

Here's a nice round up of some of the major breakthroughs over the past few years in the hunt to "find the genes that make us human" from Katie Pollard of UC Santa Cruz. Few surprises but a good precis of her own efforts to find HARs - highly accelerated regions of DNA that have lain conserved in mammalian genomes for millennia and then sprung to evolutionary life uniquely in humans. FOXP2, ASPM and AMY1 - all dealt with extensively in NOT A CHIMP - also get a look in.

Dogs out-smart chimps in Harvard exams

Here's a new addition to the "dogs are the new chimps" line I flagged in the side-bar. It specifically relates to the ability of dogs to accept a variety of cues from a human as to the location of food. A task chimps fail miserably. The key point here is that, despite being further away from us genetically, dogs have evolved a superior form of social intelligence to chimpanzees in certain areas. Picking up clues from humans being one of them. See chapter 8 in NOT A CHIMP for more details.

Could early humans climb trees?

The term "hominin" came into fashion a number of years ago to denote the "bipedal apes" - meaning extant humans and all human ancestors since the split from the common ancestor 6 million years ago - as opposed to any of the other great apes. When did our ancestors become truly bipedal, and did it mean that they had to sacrifice agility in tree-climbing in order to do so? Until recently, however, there were, apparently, no good biomechanical studies of chimpanzee limbs versus hominin limbs that could settle the matter. Now, Jeremy DeSilva has compared the detailed anatomy of talus (a bone in the lower ankle) and tibia (shinbone) between a number of chimpanzees and fossil early humans dating back to 4.12 million years ago. He finds that "chimpanzees engage in an extraordinary range of foot dorsiflexion and inversion during vertical climbing bouts" - far in advance of that which the early human ankle was capable. He concludes that, if early hominins could climb trees at all, they were doing it "in a manner decidedly unlike modern chimpanzees."

Neoteny in gene expression in human brain

In chapter 11 of my book I describe the process by which I believe humans domesticated themselves, compared to chimpanzees. The principle idea evokes a process called neoteny, first described by Ashley Montagu and Steven J Gould, which involves so-called heterochronic shifts in the timing of development from foetus to adult - a staggering or delaying of the developmental clock such that important stages in development get prolonged and delayed. For e.g. childhood and adolescence. Corresponding changes in body, skull and jaw morphology are noticed as a result of neoteny, which might explain Homo sapiens' more gracile morphology. Although neoteny has been reported in the pattern of switching on of flows of adeno-corticoseroid stress hormones and some brain neurotransmitters, this concept has not been applied to gene expression - the timing of active protein production in genes. Now a research group including Philipp Khaitovich and Svante Paabo has reported just such a study, documenting a startling number of genes exhibiting delays in their protein-producing activity unique to humans. These genes are all active in the pre-frontal cortex, evolutionarily the most recent, and advanced, part of the human brain and seem mainly concerned with growth and development of grey matter. "There is a human specific neotenic shift in gene expression during postnatal maturation of the human prefrontal cortex, causing adult humans to resemble juvenile chimpanzees in their expression profiles." Importantly, they point out, the period when this delayed gene expression finally kicks in corresponds to the period of dramatic re-sculpting of synapse connections in the brain which we associate with late adolescence and early adult maturity - when the pefrontal cortex is finally taking on its adult organization. "Delayed grey-matter maturation in the human prefrontal cortex may extend the period of neuronal plasticity associated with active larning, thus providing humans with additional time to acquire knowledge and skills". As the father of a late-teen son, I sincerely hope they are right!!