Natural selection continues apace in nature, but modern medicine is subverting the process in humans, writes DICK AHLSTROM
Birds do it, bees do it, but do we? Evolution through natural selection is alive and well and making changes in all the species on the planet, but where is it taking us?
Scientists can actually watch the process in organisms such as viruses, bacteria or fruit flies.We know evolution is real because we can apply environmental pressures to drive genetic change in these quickly regenerating species.
It is more difficult to watch in “real time” in humans and mammals, since change evolves slowly over many generations. In this case, the fossil record helps, by, for instance, showing us what our earlier human-like ancestors looked like and what changes occurred.
One way or another change arrives, brought either by external environmental factors working directly on our genes or by spontaneous mutation. And most of the change is spontaneous, says Prof James McInerney of the Department of Biology at NUI Maynooth.
A case of mistaken identity
“The vast majority of evolution is neutral, it is not in response to an external influence. It is because the [gene] replication system makes mistakes,” says Prof McInerney, currently a visiting professor at Harvard University in the US.
This may seem like a bad thing but it is just the opposite. “We need to have genetic variety or pathogens will bring us down. We have to be evolvable,” he says.
“Evolvability is good. We could evolve to a position where our replication system doesn’t make mistakes but that is a very bad idea. The ability to be different turns out to be a good idea a lot of the time.”
The parts of our genomes that change the most, however, are the ones that interact with external forces. “How we interact with the environment makes for most of the change,” says Prof McInerney.
A plague on just one of your houses
He cites an extreme example: the waves of Bubonic plague that swept Europe. Some people survived better than others. “The bacterium that was afflicting the population had a different effect on one blood group than another,” he says. Those who survived passed these resistance genes on to subsequent generations.
Sickle-cell disease is another example, says Prof Aoife McLysaght of the Molecular Evolution Lab at the Smurfit Institute of Genetics at Trinity College Dublin.
This red blood cell-related condition causes anaemia in sufferers, but having it confers an advantage, with the person being less affected by malaria, she says.
“Evolution does a cost/benefit analysis. The benefit of protection against malaria outweighed the cost of being anaemic.”
This kind of natural selection is under way all of the time, but do we have any idea where it is taking us? “Human evolution is still going on but it is hard to know where it is heading,” says McLysaght.
Prof Dan Bradley, professor of population genetics at the Smurfit Institute, agrees. “It is hard to predict because we don’t know what the future holds. But we can’t look at the present and assume we will continue on a straight line.”
One thing is certain, however. “The biggest drivers of evolution are death and disease.” When these hit they make changes for better or worse and this can be seen in the genome. “It is written in our genes.”
We can see some physiological changes, such as eye-colour change or height, says Prof McInerney.
“Look at height in humans. You can go to any medieval castle and have to squeeze your way through the doors. There is some kind of selection for tall genes, perhaps sexual selection, but genes for height are making their way through.”
Immune-system change is certain, matching that posed by evolving infectious agents such as Sars and influenza. Genes relating to nutrition are also evolving. “For example, there is a gene duplicated in Asians, but just a single copy is found in Europeans. [It is] a gene to break down starch as rice. And we could be undergoing evolution now to improve ability to remove fatty foods from our diet,” he says.
Natural selection can confer benefits but its workings are random, says Prof Kevin Mitchell, of the Smurfit Institute and the Institute of Neuroscience at Trinity. “Evolution is not directed. In hindsight it looks purposeful, but that is an illusion.”
He believes asking whether humans are evolving is the wrong question: “You should ask is natural selection acting on humans and . . . the answer is yes.”
Ironically, we have found ways to thwart it, for example through modern medicine. There is “artificial selection” when an embryo’s DNA is pre-screened for genetic diseases. Demand for this service will likely expand, he says.
“Natural selection is frustrated in human society,” says University College Cork emeritus professor William Reville. Modern medicine saves the lives of many who in the past would have died.
Could genetic mutation create superheroes?
If natural selection promotes useful genes and passes them on through the process of evolution, could something extraordinary arise from the process? Could we develop new capabilities such as the ability to read minds or levitate?
The evolution of amazing powers through genetic mutation is the premise behind the X-Men film series. The mutants are otherwise ordinary humans who have evolved powers they can use for good or evil, depending on whether they are goodies or baddies.
Magneto can manipulate magnetic fields strong enough to rip up the Golden Gate Bridge. Cyclops can ignite objects just by looking at them and Storm can control the weather.
Natural selection may bring improvements, but there is a simple reason why these exotic powers will not be among them. You can't ignore the laws of physics, says Dr Cormac O'Raifeartaigh, a physics lecturer at Waterford Institute of Technology.
"You can't create energy out of nothing," he says of powers such as Storm's or Magneto's. The film's Prof Xavier can read minds but there is no way to transmit thoughts without some physical carrier.
"We are always reluctant to rule something out but I can't see how a genetic mutation would give rise to such powers," says O'Raifeartaigh.
DICK AHLSTROM
