ABOUT 32,000 years ago in the south of France, humans decorated the walls of the Chauvet cave with elaborate scenes of animals. These paintings are among the first evidence we have that ancient humans observed and recorded the world around them.
Philosophers have also pondered the biological order of our planet and, despite the fact that many were unsure of the origins of life, they were able to deduce that organisms survived and reproduced if they were fit to provide for themselves.
But it wasn't until 1859, when Charles Darwin wrote On the Origin of Species by Means of Natural Selection, or, The Preservation of Favoured Races in the Struggle for Life, that we had a workable idea of how species evolved.
Dr Luc Bussire, an evolutionary biologist at Stirling University, describes Darwin's theory as "evolution by natural selection, meaning that genes that help individuals survive and reproduce tend to increase in frequency within populations".
Unfortunately, says Dr Nick Colegrave, of Edinburgh University, "Darwin was unaware of (Gregor] Mendel's work into genetic inheritance". It wasn't until after Darwin's death that it was widely realised that the tool kit which parents passed to their offspring was contained in their genes.
Many years later, Professor Richard Dawkins proposed the "selfish gene" theory, which, according to Colegrave, was an attempt to formalise "what it is that benefits from natural selection". He says: "It will usually be the case that what is best for the gene will also be best for the individual, but in situations where their interests differ, selection for the gene's interest will dominate."
An example is a male spider, who is often eaten by the female after mating. This is obviously not good for the male, but offering himself as a nutritious snack may help the female to provide for the offspring that contain his genes.
However, Stephen Jay Gould and Niles Eldredge highlighted that the gradual pace of evolution suggested by Darwin didn't fit with fossil records. So, Eldredge and Gould proposed that, based on fossil records, at key points an evolutionary explosion results in many new species. They called their theory "punctuated equilibrium".
According to Bussire, the truth probably lies somewhere between extreme versions of gradualism and punctuated equilibrium.
So, if we accept evolution occurs at variable speeds, what causes the shift in gear?
Dr Keith Skene, of Dundee University, suggests that a change in available energy is the main driving force. He argues that a decrease in energy, for example from the smoke of a huge volcanic eruption blocking out the sun, causes organisms to become extinct. This then creates niches which surviving organisms can evolve to occupy. As Skene puts it, "evolution occurs in the empty marketplace, not the crowded back alleys".
This is just one of the biological themes that Skene eloquently describes and then encourages us to think about and challenge in his book, Shadows on the Cave Wall; A New Theory of Evolution.
He also questions whether The Origin of the Species would be the same if Darwin had been aware of the existence of bacteria when he wrote it. Bacteria happily share genetic parcels between each other, regardless of whether they belong to the same "species". Therefore, the concept of a genetically defined species doesn't really apply to bacteria. "This is a very exciting question," says Colegrave. However, after agreeing that knowledge of bacteria may possibly have affected Darwin's thoughts on evolution, he says that "the passage of genetic material between bacteria still fits with the theory that the gene is key in evolution".
Dr Skene believes that we need to spend less time asking how and increasingly ask why evolution occurs. Skene argues that energy is the main reason behind why evolution occurs, and that this force that acts at all levels of organisation on our planet surpasses the gene as the driver of evolution. He states that everything on the planet needs to obey the laws of physics and, more specifically, the laws governing energy.
When you think about it, this seems logical – but is it a new scientific theory? Luc Bussire argues that Skene's arguments are presented for a generalist reader, which makes them difficult to test in a scientific way. Nick Colegrave agrees, but adds: "Skene's book contains some lovely biology and will hopefully encourage people to think more deeply about the interaction between evolution and the environment."
Will Skene's ideas have an impact on evolutionary biology? It is difficult to know. But his book will remain an attention-grabbing read for anyone interested in the subject.