Be it in sports or comedy, they say that timing is everything. In evolution, it’s no different. Many of the innovations that have separated us from other apes may have arisen not through creating new genetic material, but by subtly shifting how the existing lot is used.
Take our brains, for example. In the brains of humans, chimps and many other mammals, the genes that are switched on in the brain change dramatically in the first few years of life. But Mehmet Somel from the Max Planck Institute for Evolutionary Anthropology has found that a small but select squad of genes, involved in the development of nerve cells, are activated much later in our brains than in those of other primates.
This genetic delay mirrors other physical shifts in timing that separate humans from other apes. Chimpanzees, for example, become sexually mature by the age of 8 or 9; we take five more years to reach the same point of development.
These delays are signs of an evolutionary process called “neoteny“, where a species’ growth slows down to the point where adults retain many of the features previously seen juveniles. You can see neoteny at work in some domestic dog breeds, which are remarkably similar to baby wolves, or the axolotl salamander, which keeps the gills of a larva even as it becomes a sexually mature adult. And some scientists, like the late Stephen Jay Gould, have suggested that neoteny has played a major role in human evolution too.
As adults, we share many of the physical features of immature chimps. Our bone structures, including flat faces and small jaws, are similar to those of juvenile chimps, as is our patchy distribution of hair. A slower rate of development may even have shaped our vaunted intelligence, by stretching out the time when we are most receptive to new skills and knowledge. Somel’s research supports this idea by showing that since our evolutionary split from chimpanzees, the activation of some important brain genes has been delayed to the very start of adolescence.
You’re looking at the face of a new species of fish and judging by the two fearsome fangs, you’ll probably understand how it got its scientific name – Danionella dracula. The teeth do look terrifying but fortunately, their owner is a tiny animal just 15 millimetres long. Ralf Britz from London’s Natural History Museum discovered the fanged fish in a small stream in northern Burma, just two years ago. The more he studied them, the more he realised that they are physically extraordinary in many ways.
For a start, those are no ordinary teeth – they are actually just part of the fish’s jawbone. True teeth are separate from the jaws that house them and are made of several tissues including enamel and dentine. Those of D.dracula are protrusions of the jaw itself and are made of solid bone. The fish has rows of them in both its upper and lower jaw that look very convincingly like actual teeth. Even though it comes from a long line of fish that have lost their teeth, D.dracula has managed to re-evolve them through a completely unique route.
Secondly, D.dracula seems to be missing several bones, with 44 fewer than close relatives like the zebrafish, Danio rario. They haven’t disappeared – they never formed in the first place. Compared to other related fish, D.dracula stops developing at a much earlier point and retains the abridged skeleton of a larva throughout its adult life. It’s the Peter Pan of the carp family.