Evolution is unstoppable and undirected, but sometimes things go horribly wrong ...
1 THE ETERNAL BANANA
It’s the second most eaten fruit in the world (behind tomatoes) but, honestly, the evolutionary future of the banana is bleak.
Really a berry, bananas originally came from Southeast Asia and far northern Australia. In the wild, most have large hard seeds that make the fruit almost inedible. However, there is a genetic mutation that occurs every now and again that stops the seeds from developing in the usual way, leaving instead nothing but sweet delicious flesh.
All that remains of the seeds are the slightly dark stripes near the centre. Go have a bite and look for yourself.
About ten thousand years ago somebody somewhere began to cultivate these scrumptious seedless mutants from cuttings, and they spread around the world.
Cultivating from cuttings is basically cloning; banana plants send up new shoots that are cut from the plant and potted out to start a new plant in a process called parthenocarpic (seedless) vegetative propagation. Today we still eat the descendants of those first cuttings.
So, what’s the big deal? Well, first of all, most banana plants are genetically very similar because they are essentially clones of each other, so they lack the kind of variation that evolution needs.
Without seeds the banana is also sterile. It can’t reproduce on its own, therefore it can’t pass down variations even if it had any. If the environment changes, or a disease arises, the world’s bananas will be unable to evolve and adapt and will most likely be wiped out. Human beings have made the familiar banana into an evolutionary dead-end, albeit a delicious one.
2 LIVING FOSSILS
Ferns are old. Really old. They first appeared in the fossil record roughly 360 million years ago.
In 2014, researchers discovered the incredibly wellpreserved 180-million-year-old stem of a royal fern (Osmundaceae) in Sweden. It had been rapidly turned to calcium carbonate sometime in the Early Jurassic period.
The specimen, preserved in a bed of volcanic rock, was so perfectly fossilised that under a microscope, scientists could see the contents of the fern’s cells. They could see the cell nucleus and, in some cases, even the chromosomes as they split during cell division.
The scientists decided to compare the fossil with its nearest living relative, the cinnamon fern, Osmundastrum cinnamomeum, which itself is rather ancient, dating back 75 million years. What they discovered was incredible.
The two were nearly identical. They appeared to have the same number of chromosomes and even the same DNA content, meaning the fern had come to an evolutionary standstill for 180 million years.
As they say, if it ain’t broke, don’t fix it.
3 WHICH BEETLE IS BEST?
Sometimes evolution can be actively taking place, but still be at a standstill. It’s like running on the spot.
Sexual selection, as proposed by Charles Darwin, takes place within and between the sexes of many species. Darwin divided this into two forms: male combat and female choice, but today we know there are even more ways that it happens. One is an antagonistic co-evolutionary relationship between males and females.
Graphoderus zonatus, a species of Swedish diving beetle, is an example. The males have developed suction cups in their front legs in order to hold on to the shells of females during mating. As mating can last for hours, females can be damaged by these cups. To avoid this, a portion of the female population developed rougher shells, which are harder to hold on to.
In response, a corresponding portion of the male population developed new suction cups designed to grip these rougher shells. Thus, the population is split into two groups: the smooth shelled female/male pair, and the rough shelled female/male pair. Normally, this is the beginning of a split and the formation of two new species. Not this time.
If the smooth shelled female/male pair becomes dominant, the damage the males do to the females gives the rough shelled female/male pair an advantage. And the same thing happens if the rough shelled female/male pair become dominants. Weirdly, selection favours the different variations equally, and every time the numbers of one pair rise, they are brought down by the other pair, thus keeping the species at an evolutionary standstill.
4 IT’S A TRAP
While plenty of organisms become extinct though natural processes, humans seem to have a knack for destruction.
Nearly 20 years ago in Nevada, US, a rancher introduced a plant species, Plantago lanceolate, to a meadow on his property. An isolated population of Edith’s checkerspot butterfly (Euphydryas editha) began to develop a taste for this new perennial species over its traditional annual food source, Collinsia parviflora. Being a perennial, the new kid on the block provided food all year round.
By 2005 all the butterflies in the meadow had evolved to eat and lay eggs on Plantago exclusively, thus setting an evolutionary trap.
When the rancher died, the meadow was no longer used for cattle grazing and quickly tall grasses sprang up, overshadowing the smaller Plantago, leaving the heat-loving butterfly larvae in the shade and surrounded by new predators that came with the grasses. The trap had been sprung.
By 2012 the Edith’s checkerspot butterfly population on the ranch was extinct. Lured by the evolutionary trap to evolve to a specific form of land use, the butterflies found themselves in an evolutionary dead-end when the land was used in a different way, causing selection to turn against them.
5 STOP!
Evolution is an engine of change and generates a wealth of variety in the living world. Because of this, it’s a never-ending source of wonder. But sometimes the relentless process of adaptation and transformation can cause humans serious problems.
The development of antibiotics is perhaps the greatest achievement of modern medicine; drugs that can stop a huge variety of malevolent bugs in their tracks, leaving us free from infections and many horrifying diseases.
But now there are antibiotic resistant strains of microbial species, and this is one of the more serious issues facing humanity. Already there are antibiotic strains of the dangerous bacteria Staphylococcus aureus, and the pathogen that causes tuberculosis. This is happening mostly because humans often don’t take the full course of antibiotics prescribed by doctors. They start to feel better and stop.
But what does this do? It leaves behind the bacteria that have survived the antibiotics the longest; the strongest, most resistant bacteria. These then reproduce and the species becomes increasingly resistant to our attempts to counteract them.
Recently, researchers uncovered what might be a way to stop these nasty little bugs from evolving into superbugs.
When exposed to antibiotics, a process called the ROS response causes the DNA of bacteria to become damaged. The cells try to repair this, but some are very prone to errors, which causes lots of variation in the form of genetic mutations. Now, while most of these mutations are neutral, damaging, or fatal, every now and again these mutations help the bacteria to resist the flood of antibiotics.
However, there are numerous drugs already on the market that suppress the ROS response in humans, and scientists have found that using these along with antibiotics can stop the generation of new genetic variation while killing all the bugs present.
Denied one of the key ingredients of evolution – variation – the bacteria are stopped from evolving into new resistant strains
6 NO MORE EVOLUTION FOR US
Although the view is controversial, some scientists argue that human beings, at least in Western countries, are no longer evolving.
Natural selection works using a combination of differing rates of reproduction and differing rates of survival to reproductive age. Organisms well adapted to their environment tend to have more offspring, and over time they occupy a larger and larger percentage of the population.
But they can’t do this unless they survive to actually, you
know, reproduce. Some researchers suggest that the medicine, nutrition and public hygiene measures of the Western world are all allowing a huge percentage of the population to survive to reproductive age.
Genes, good and bad, adaptive and damaging, are all making their way into the next generation. Basically, the Western lifestyle, it seems, is stopping selection from happening.
Unless there is huge environmental change (which there may well be if human-generated climate change is allowed to continue unchecked) humans in the Western world won’t evolve any more, because you can’t have evolution without one of the three key ingredients: natural selection.