Sex is costly. Yet it is widespread throughout the animal kingdom, so there must be some advantages to it. And still, it seems easier to list disadvantages. Sexual reproduction is complicated, requires more time and uses more energy than its asexual counterpart. Partners have to find each other and coordinate their activities to produce the next generation. Another problem is the so-called ‘cost of meiosis’, meaning that, in sexual reproduction, only half of the genome is passed on. Compared to an asexually producing individual which passes on its entire genome, this is a high cost indeed. Another cost is the production of males that will not all succeed in reproducing, and thus waste resources.

Once upon a time, tool use was considered to be a uniquely human feature, setting us apart from the rest of the animal kingdom. But, when Jane Goodall observed chimpanzees using sticks to ‘fish’ for termites (see video 1) in the 1960’s, this idea received a serious blow. Since then, tool use has been observed in a variety of animals, ranging from the usual primate suspects, to less expected critters, such as crows, dolphins, elephants, otters and even octopuses (see video 2).

Video 1: Chimpanzees using tools to 'fish' for termites.

(Source: BBC documentary 'Cousins')

Apparently, the female ancestor of present-day polar bears was a brown bear, living in what presently corresponds to Ireland. An international research team has used mitochondrial DNA (see figure 1) to trace back the polar bears (maternal) ancestry. And it turns out that, 20,000 to 50,000 years ago, they interbred with brown bears.

Figure 1: During fertilization, the sperm cell does not contribute mitochondria to the egg.