Life pits the order and intricacy of biology against the ceaseless chaos of physics. The second law of thermodynamics, or the thermodynamic arrow of time, states that any natural system will always tend towards increasing disorder. Biological ageing is no different, making death inevitable. However, one of the least-addressed questions of ageing is the apparent paradox between the optimizing drive of evolution, and the inevitable deterioration of the body.
Modern medicine’s ability to keep us alive makes it tempting to think human evolution may have stopped. Better healthcare disrupts a key driving force of evolution by keeping some people alive longer, making them more likely to pass on their genes. But if we look at the rate of our DNA’s evolution, we can see that human evolution hasn’t stopped – it may even be happening faster than before.
Whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved. So wrote Charles Darwin, in his On the Origin of Species. The origin and evolution of animals is one of the most fascinating questions in modern biology.
Most animals have brains in proportion to their body size – species with larger bodies often have larger brains. But the human brain is almost six times bigger than expected for our bodies. This is puzzling, as the brain is very costly – burning 20% of the body’s energy while accounting for only 4% of its mass.
Until recently, anthropologists drew the human family tree in the same way that my 10-year-old son solves a maze. He finds it much easier to work from the end to the beginning, because blind alleys lead with depressing sameness away from the start. In just this way, scientists once traced our own lineage from the present into the past, moving backward through a thicket of fossil relatives, each perched upon its own special branch to extinction.
DNA sequencing technology is helping scientists unravel questions that humans have been asking about animals for centuries. By mapping out animal genomes, we now have a better idea of how the giraffe got its huge neck and why snakes are so long. Genome sequencing allows us to compare and contrast the DNA of different animals and work out how they evolved in their own unique ways
When the dinosaurs were wiped off the face of the planet, how did they leave? Was it a slow, plodding decline or a short sharp bang? Back in the 1960s and 1970s, debate about this question was mainly taking place on the ground, at fossil sites in places like Montana. Paleontologist Robert Sloan and his colleagues documented evidence for the long-term decline of dinosaurs over a 10m to 20m-year period. Dinosaurs had been losing out, ever so slowly, to the rising mammals, mainly as a result of cooling climates.
We’re all here because of mutations. Random changes in genes are what creates variety in a species, and this is what allows it to adapt to new environments and eventually evolve into completely new species. But most random mutations actually disrupt the functions of our genes and so are a common source of genetic diseases.
Speculating about what aliens look like has kept children, film producers and scientists amused for decades. If they exist, will extra terrestrials turn out to look similar to us, or might they take a form beyond our wildest imaginings? The answer to this question really depends on how we think evolution works at the deepest level.
In scientific research on human impact the focus is usually aimed at the extinction of species. Nowadays however, scientists are becoming more and more aware of the fact that trough, for example animal domestication, we have also become a driving force of evolution. This driving force that has led to new species, traits and ecosystems.
Biomedical researchers like me probe the mechanistic basis of health and disease. In a long career working at the discovery end of the spectrum, I’ve been privileged to live through, and make some small contribution to, an extraordinary (and continuing) revolution in medical understanding and human well-being.