A general theme of all A-Level Biology specs is that of adaptation. Organisms have special features that enable them to survive in a particular environment. This links nicely into evolution by natural selection as the adaptation provides an individual with a selective advantage so they survive in the selection pressure and go on to reproduce to pass on their advantageous alleles (that gave them the adaptation) to their offspring. Over many generations, this causes a change in the population of a species as the advantageous allele frequency increases. The population changes to be more adapted to the selection pressure. With climate change causing great changes in the environment, new selection pressures arrive. If a population can’t change to survive the new selection pressure, there is a risk of population extinction – it’s a worrying time. One common error students make on exam papers is to consider this scenario at a species level – in other words a new selection pressure will cause the extinction of a species. This would only be the case if the species were down to its last few populations, so very unlikely in the first instance, so this expression should be avoided. So, it’s not the species that adapts to the new selection pressure, but the population.

Adaptations must be rooted in genetics and we can see this in action in two populations of polar bears in Greenland – one population living in the colder parts in the northeast and the other in the warmer southeast.

The scientists were focusing on transposons – these are known as jumping genes because randomly these DNA sequences move to other locations within the genome. This can have an effect on whether genes are expressed or not. RNA sequencing was used to show which genes were being expressed and which were not. This analysis showed a large population difference. The polar bears in the warmer environment had evidence of new gene activity to help them cope with heat stress, aging and metabolism. As global warming continues and sea ice melts, this population is adapting. Whilst this survival change is heartening, it is only one population – the species still remains under threat from global warming. This is further evidence of how we must reduce fossil fuel use and prevent the global temperature from increasing any further.

The other part of the article was about the environmental changes in North America causing two different species of bear – polar bears and grizzly bears – to have overlapping habitats for the first time. Members of the two species are interbreeding and hybrids have been born – When it is a mating between a polar bear father and a grizzly mother they are called “Pizzly bears”. This research was covered by the New Scientist. But there was a feature of a female polar bear having cubs after mating with grizzly bears – these cubs are called “grolar bears”. What is striking about this research is these grolar bear cubs matured and were able to have their own cubs – so not sterile hybrids as you would expect, but fertile! Is this unusual occurrence a way of adapting to global warming? But mixing of species genomes in this way could potentially cause the species’ genomes to be changed so much the original polar bear species genome in particular is lost forever.

Download the article from the IFL Science page here

Download the article from the New Scientist page here