Addendum: An earlier version of this story contained a typo in the word swath.
Charles Darwin did a fine job of showing why his theory of evolution explained the living world better than any creationist ideas could, and evidence has piled up ever since, but a wide swath of the American public remain unconvinced. Therefore, it’s always good to come across new scenarios to show how evolution works and debunk some of the misconceptions spread by proponents of “intelligent design” and other versions of creationist mythology.
On the surface, coffee might seem like a good candidate for a plant that was not only designed by an intelligent god but by a god that was feeling rather benevolent toward us humans. After all, this plant produces a bean – technically a seed – that smells heavenly, tastes satisfying, makes us feel good, and isn’t even bad for us.
There used to be some confusion but now, scientists have had the chance to observe lots of coffee drinkers for long periods of time and not only do they find no connection with heart disease or cancer, but they even see hints that those who indulge regularly may be less likely to get liver cancer or type 2 diabetes.
Rob van Dam, a professor of nutrition associated with the Harvard School of Public Health, said some of the confusion in the past came from the fact that coffee is so pleasant to drink that it was favored by indulgent type people – those who slept too little, drank a lot of booze and smoked a lot of cigarettes. By association it seemed that coffee ought to be bad. And the fact that it was mixed up with various unhealthful habits made it hard for the experts to detangle things and tell us whether coffee was good or bad for health.
Some of the best data we have on coffee now comes from the Nurse’s Health Study and the Health Professionals Follow-up Study, said van Dam. When looking over lots of people for decades, coffee looks to be, if anything, a healthy choice for most people. But there’s still more to learn, he said, since coffee packs a huge number of different compounds, caffeine being just the most popular and well known.
All this raises the question of how evolution alone could produce something so complex and so wonderful. Not that there was any doubt, but scientists now have the story pretty well fleshed out after deciphering the DNA of the coffee plant in a project known as the Coffee Genome Project. The results were published earlier in September in the journal Science.
Victor Albert, a biologist at the University at Buffalo, who was part of the effort, said that there will be important applications for coffee growers. How could such a study fail to be useful considering there are 2.5 billion cups of the stuff consumed every day?
There are a bunch of species of coffee, only a few of which make caffeine, said Albert. The genome analysis used robusta coffee, which makes up about a third of coffee consumed. The other popular species, arabica, is a hybrid of robusta and another species.
For Albert, the work is exciting because it’s telling us something about evolution.
Sometimes creationists claim that a series of genetic mistakes can’t add up to make plants or animals more complex, or in any way improve them. This is wrong, and the coffee genome shows exactly how evolution can make a plant more complex and, to human tastes, improve it.
Flowering plants appeared around 160 million years ago. Once they arose, said Albert, they quickly spread and divided into an array of forms fantastically diverse in their chemistry and appearances.
What the DNA reveals, is that early in the history of plants, the entire complement of DNA – the genome – doubled. That is, instead of making a typo, some plant simply got two copies of everything. “With all these duplications you have an opportunity for the duplicates to take on new functions and make progeny that are more adaptive,” he said. It’s like getting new blank canvasses upon which evolution can start innovating.
Dr. Albert said this duplication happened by accident a few times on various branches of the flowering plants, and he suspected it might have happened in the coffee lineage. What they found instead, he said, was not that the whole complement of DNA doubled, but that one key gene was copied a couple of extra times, and the copies mutated to become variations on the original theme. Between them, they produced several different enzymes that acted as catalysts to synthesize caffeine.
Making caffeine is a multi-step process, he explained, and each time the gene doubled, the duplicate was altered so that it catalyzed another step in the reactions from caffeine precursors to caffeine.
If this all seems too complex to have happened without magical intervention, keep in mind that the precursors are useful to plants too, since they are bitter and toxic to some animals – thus protecting parts of the coffee plant from being eaten. One of the precursors to caffeine, for example, is theobromine, which is in chocolate. It’s toxic to dogs and probably some herbivorous animals as well.
But caffeine appears to be extra beneficial to plants since it evolved through different genetic mutations in coffee, chocolate and tea – a phenomenon called convergent evolution. We know why we like coffee, but what’s in it for these different plants?
For that, I asked biologist Julie Mustard from the University of Texas, Brownsville. A few years ago she had been studying ethanol addiction using bees when she learned that some plants, including coffee, make caffeine in their nectar. Nectar is the sweet tasting stuff that rewards bees for pollinating them. Could the plants be attracting the pollinators the way
To find out, she and Jeri Wright, who is now at Newcastle University, started to do some experiments with bees comparing their responses to nectar with and without caffeine.
Bees can be trained something like Pavlov’s dogs, which famously salivated when they learned to associate a bell with food. In the case of the insects, she said, they will stick out a tongue-like proboscis when smelling flowers they’ve learned to associate with nectar. In her experiments, she found bees formed much stronger positive associations with the flowers that produced the caffeinated nectar, she said.
The bees can’t smell the caffeine, and it tastes bitter. So what’s the draw? “It acts as a neurochemical that interacts with the reward pathway and bees keep coming back to those plants that make the caffeine,” she said. In other words, they enjoy it and they get hooked. That’s good for the plant, because it’s more likely to get pollinated and thereby reproduce. We humans just got lucky that we share some basic brain chemistry with our fellow animals, including bees, so we, too, can get a buzz.
