By BBC Wildlife Magazine

Published: Tuesday, 15 November 2022 at 12:00 am

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What is evolution?

From bacteria to blue whales, all life on Earth owes its existence to a process of deceptive simplicity yet astonishing power: evolution. It drives the diversity of living creatures and reveals how seemingly miraculous traits can emerge from the need to survive. It also provides the insights needed to create new organisms to order. 

Small wonder that evolution is so controversial. Long regarded as primarily a way of understanding past life, it is now at the forefront of concerns about the future. How can we protect species from environmental change? What are the dangers of using evolutionary processes for our own ends? 

Nor is the impact of evolution restricted to global issues. From the emergence of antibiotic-resistant ‘superbugs’ to the selective breeding of plants and animals, its effects are manifest at every level of life.

Fundamentalists insist that all life is the act of a divine creator. Scientists claim that the processes of evolution continue to work miracles to this day. 

• Does the tree of life reflect evolution?
• Endosymbiosis guide: what it is and why complex life needs endosymbiosis
• Phenotype guide: what it is, it’s relation to the genotype and the effect on evolution
• Speciation: what a species is, and how new species form
• What are chromosomes and why are chromosomes important?

How does evolution work

At the core of evolution is change: how living organisms change in the face of changing environments. It was modifications to the beaks of finches that led Charles Darwin to first ponder the idea of evolution in On the Origin of Species. But the process by which these alterations took place was harder to explain. Darwin knew from animal breeders that the changes were random – yet they also had to be capable of being inherited by future generations, or they would be of only fleeting benefit. 

It is now known that such developments take the form of random mutations of genes, the chemical instructions inside every living cell. Genes can be mutated by many means, from exposure to radiation, to blunders by the gene-reading mechanisms of cells. Most mutations are harmful, and are likely to be eliminated by the body or cause premature death. But, if the organism can breed, the mutations are passed on via DNA to its offspring. 

While mutations produce change, their random nature makes them inefficient at creating organisms suited to their environments. With even simple bacteria having thousands of genes, the probability of organisms developing beneficial mutations by chance alone are tiny. What is needed is a filter
to boost the effect of beneficial mutations. That filter is natural selection – the name coined by Darwin to describe the influence of the environment on living organisms. 

Natural selection ensures that beneficial genes are singled out through their effect on reproductive success. For example, a mutation that makes an organism more able to defend itself has a better chance of being passed on than one that leads to premature death. Working together, random mutation and natural selection are astonishingly effective at producing successful organisms. It explains not only how life came to be as it is now,
but also how it continues to change.