More on pseudo-genes...
An obsolete vitamin C factory is not the only relic of our evolutionary past lurking in our genome. There are instructions in our design manual for all sorts of parts that our bodies no longer build. Consider for example our sense of smell.
We have a collection of proteins called olfactory receptors each one being produced by a different OR gene. Compared with other animals our ability to detect odours is poor, which should not really surprise us. We depend far more on vision than other animals. Nocturnal creatures in particular have exceptional smelling abilities.
Now if evolution is correct there was a time in our distant past when we must have relied on our sense of smell much more than we do today. If that were the case then you would expect to find evidence for it in our genes. Remember genes that are no longer needed suffer mutations with impunity but their remains can still be found as incomplete sentences in our ‘recipe book’ as pseudo-genes.
Geneticists Linda Black and Richard Axel won the Nobel Prize in 2004 for their work on OR genes. They discovered that humans have 800 such genes but fully half of these are inactive relics of our much smellier past. As our brain combines signals from a number of receptors simultaneously that means our sense of smell is only a fraction of what it once was.
What though of our closest relatives? Well not surprisingly there was found to be a direct correlation between the closeness of our evolutionary cousins and the number of active and inactive OR genes.
Why should dead genes show such a relationship if not for evolution? We carry this genetic baggage because it was needed in our distant ancestors who relied on a keen sense of smell for survival.
Clearly a mechanism that enables us detect airborne odours is not going to work the same under water. So what about aquatic mammals like dolphins? If they really were once land animals as evolution claims, there should still be evidence in their genome that they once had an acute sense of smell.
Not surprisingly the evidence is irrefutable, genes don’t lie. 80% of the OR genes in a dolphin are inactivated; hundreds of them remain in their genome as silent testimony to their evolutionary past. The DNA sequences of those dead genes resemble those of land mammals.
In other words dolphins have the instructions in their genes to construct the tools for detecting thousands of airborne smells. This makes no sense if dolphins were specially created.
Obviously the receptors that detect odours in water are different from those that work with airborne smells. In fish we find one kind of OR genes and in amphibians and mammals there is another.
The most primitive fish still alive today is a jawless fish called Lamprey. Fossils of these creatures 320 million years old bear a very close resemblance to it’s modern cousin. When the DNA of the lamprey is studied it turns out their OR genes are neither air nor water specific; they combine features of both. These creatures arose before smelling genes split into two types.
Like all our other genes our OR genes for odour detection tell a story of our species’ past. They are similar to primates, less similar to other mammals, less similar still to reptiles, amphibians and fish in that order.
