As a rule, all mammals have the same number of vertebrae in their necks, regardless of their necks’ length. Among other animals, like birds, reptiles and amphibians, there’s a little more variety: the long, slender necks of swans have 22-25 vertebrae, while bullfrogs’ necks have just one. Mammals, though – whether they’re a Kitti’s Hog-nosed Bat (the smallest mammal), a blue whale (the biggest) or anything in between – always have seven.

There appears to be good reason to follow the trend. Too many or too few neck vertebrae are associated with stillbirth, childhood cancer, neuronal problems and misplaced or crushed nerves, muscles and blood vessels in humans and some other mammals. Any change in the vertebrae number is probably selected against to avoid these problems, conserving basic mammal body plans in the process.

Rules are made to be broken, though, and both sloths and manatees have abnormal numbers of neck vertebrae. Two-toed sloths (Choloepus) have five to seven neck vertebrae, three-toed sloths (Bradypus) have eight or nine and manatees (Trichechus) have six.

Neither sloths nor manatees seem to suffer from the problems that other species have when they diverge from the seven-vertebrae template, though, and a team of scientists from Austria and the Netherlands think they know how they animals are getting away with it. [Read more]

Only about 10 percent of the world is left-handed, and with good reason. My southpaw brethren and I are at an extreme disadvantage in the evolutionary race. We’ve been shown to have greater risk of schizophrenia, autism, epilepsy and learning disabilities, and are shorter lived, just plain shorter and more likely to be homosexual than righties. All that makes it difficult for lefties to attract mates, reproduce and pass on their genes, so scientists have been wondering for a long time why left-handedness persists.

A team of researchers at the Institute of Evolutionary Sciences at the University of Montpellier, France who surveyed the existing literature on the evolutionary perspectives of left-handedness, including its mechanisms and the costs and benefits acting as selective forces on the left-handed, say they may have found the secret to southpaw survival. We lefties simply had a tactical advantage in one-on-one competition.

The team’s study suggests that because lefties are in the minority, right-handed opponents may not have been used to the way they fight, and the element of surprise gave lefties an advantage. Their very uncommonness, and a good left hook jab, gave them an edge.

Because the advantage allowed them to survive physical confrontation and win resources and mates, left-handedness became more frequent over the generations through natural selection.

We can see sort of the same thing happening in the success of left-handed boxers like “Gentleman Jim” Corbett and Oscar de la Hoya and left-handed tennis players like John McEnroe and Jimmy Connors. Death isn’t on the line at Wimbledon, but everyone loves a winner, so they attract more sex partners and are more likely to reproduce.

The researchers also noted that lefties in many European countries have higher average incomes and are well represented among gifted children with high IQs. Although an advantage in fist fighting doesn’t explain that, a place at the top of the socio-economic ladder certainly promotes reproductive success, so smarts and cash should result in higher birth rates for lefties and the passing along of left-handedness.

Reference: Llaurens, V., Faurie, C. and Raymond, M. 2009 : Why are some people left-handed? An evolutioanry perspective. Philosophical Transaction of the Royal Society B. doi:10.1098/rstb.2008.0235