Category: Biology

When I was a youngster I used to do a spot of sea fishing on the freezing cold north east coast. It wasn’t so much a hobby as an obsession at one point. Key to success was a plentiful supply of lugworm which could be dug from the wet golden sand at lowtide and stored ready for the next angling venture, while ragworm, which have a nasty bite, came from the local fishing bait supplier. Never would it have occurred to my 11-year old self that these lowly creatures could harbour the secrets of our own evolution.

However, apparently it does. Detlev Arendt of the European Molecular Biology Laboratory has been studying the multifunctional neurones that sense the environment and release hormones in vertebrates (including ourselves), flies, and worms. The last common ancestor of all of these creatures must provide the evolutionary basis of our modern brains that endow us with the skills to varying degrees of success to dig up ragworm, take part in fishing trips, and ponder our origins.

Hormones control growth, metabolism, reproduction and other biological processes. In humans, as indeed in all vertebrates, the chemical signals are produced by the hypothalamus and other specialist brain centres and secreted into the blood for circulation around the body. This signalling system is not, it turns out, the preserve of those creatures with a backbone. Arendt and his colleagues now believe that the hypothalamus and its hormones have their evolutionary origins in an ancient worm-like creature that lived hundreds of millions of years ago and is the common ancestor of vertebrates, flies, and worms.

Hormones work slowly, on the whole, and have body-wide effects. Insects and nematode worms use hormones, but the specific molecules they use are very different from their vertebrate counterparts.

“This suggested that hormone-secreting brain centres arose after the evolution of vertebrates and invertebrates had split,” explains Arendt, “But then found vertebrate—type hormones in annelid worms and molluscs, indicating that these centres might be much older than expected.” Comparisons of two types of hormone-secreting nerve cells from zebrafish, a vertebrate, and the annelid worm Platynereis dumerilii, in Arendt’s lab have now revealed some stunning similarities that point to a shared and ancient ancestry for our hormonal systems.

“These findings revolutionise the way we see the brain,” says Kristin Tessmar-Raible who carried out the comparison, “So far we have always understood it as a processing unit, a bit like a computer that integrates and interprets incoming sensory information. Now we know that the brain is itself a sensory organ and has been so since very ancient times.” The research appears in detail in the journal Cell.

Bewildering to think that I used to skewer these little creatures on a barbed hook and cast them into the sea to catch scaly marine creatures. It almost makes no sense.

Here’s a puzzle. If evolution ensures that ‘good’ genes spread through a population, then why are individuals so different? Why don’t people get better and better looking through each generation to the detriment of ugliness and lead to a population of real lookers?

The problem with current evolutionary theory is that it would seem that if females select the most attractive mates, then the genes responsible for their attractive features would spread quickly, leading to all males becoming equally attractive (think peacock tails). Ultimately, further sexual selection would then no longer take place and evolution would stop in its tracks.

This is the so-called lek paradox and it has remained a foil in the weaponry of the intelligent design advocate’s arsenal for many years. Until now.

Thanks to research at Newcastle University, England, this apparent fundamental flaw in Darwin’s theory of evolution, latched on to by creationists can be explained quite effectively by evolution itself. The findings of Newcastle’s Marion Petrie and Gilbert Roberts research suggests that sexual selection leads to increased genetic diversity by a mechanism not previously understood.

Petrie reasoned that as genetic mutations occur naturally anywhere in the genome, some will actually affect those used to produce the DNA repair kit enzymes found in all cells. This would lead to those individuals with a malfunctioning or inefficient repair kit, having more mutations left unrepaired and so greater variation in their genome.

Usually, damaged DNA leads to an unviable organism that either dies quickly of the effects or is otherwise unable to reproduce. However, if those variations are present in sections of the genome responsible for disease defence, then variation can actually be beneficial as greater variation in the genome at these points means more chance of warding of bacteria and viruses.

Petrie modelled the spread of genes in a population and demonstrated that the tendency towards reduction in genetic diversity caused by sexual selection is outweighed by the maintenance in greater genetic diversity generated by mutations affecting genome repair.

The researchers began this research a decade ago and their model genes are now a great fit for the observations of variations. “We find that sexual selection can promote genetic diversity despite expectations to the contrary,” Petrie says. The team publishes details of their findings today in the journal Heredity.