Three Biological Theories that Changed the way we saw the Natural World

Cell Theory

It is often taken for granted that, for the vast majority of human history, we had no idea about the microscopic world that underpins all life. As Robert Hooke discovered in 1665, it turns out that everything that is alive is constructed from building blocks which came to be known as cells – individual packages of gloopy matter that move, breathe, eat, grow, reproduce, go about their cellular business and then die.

I wonder what it would have been like to sit at a table with a compound microscope for the first time and peer into an undiscovered realm; an invisible world that had always existed but had never been explored. Imagine looking at part of your own body from an entirely different perspective, only to find that you aren’t one living thing, but innumerable units of life all carrying out different jobs in order to sustain your existence.

A handful of soil is home to a greater number of bacteria than the total number of humans who have ever lived. According to recent research, there are ten times as many bacterial cells in your body than there are human body cells. Yes, you are more of a bacterial breeding ground than a human being, but without trillions of bacterial palls our bodies wouldn’t know how to function. It’s easy to forget that worlds too small for us to see, and too small for us to imagine, are home to the majority of living things on Earth. Everything that we know about organic life is from a perspective far removed from where most of the action is happening. 

The Theory of Evolution by Natural Selection

No list of biological theories could be complete without this bad boy.  Darwin’s famed theory sits at the very heart of what we know about life on earth. ‘Nothing in biology makes sense except in the light of evolution’ was the title of the geneticist and evolutionary biologist Theodosius Dobzhansky’s aptly named 1973 essay.

This was one of the greatest paradigm shifts of modern science; Darwin had the audacity to suggest that the church was wrong through his eloquent use of reason and evidence. He referred to three important observations that he made in his travels. Firstly, beasties in the wild tend to have more babies than could possibly survive. Secondly, no critter is exactly the same – there is always variation to some degree. It can be reasoned that some babies are born with characteristics that would help them to survive in their environment, while others would be born with characteristics that make life hard for them. Finally, and most importantly, trait differences are inheritable.

This means that the lizard born with big teeth and sharp claws is more likely to survive long enough to settle down with a nice, strong lizard ladylove and have big-toothed, sharp-clawed babies together. The poor lizard born with no teeth or claws will have difficulty surviving in a lizard-eat-lizard world, not to mention the challenge he will face in finding a spouse to pass on his genes with. This is the harsh world of natural selection: as the weak are cut back, species become increasingly adapted to their environment with each generation. Evolution is a process that had been hidden in plain sight to biologists, and Darwin had the genius to recognise it.  

The Gaia Theory

We’ve all heard the term “mother nature”; whether it be in the film Avatar or in frequent use by angry hippies to invoke some sense of sympathy for the ecosystems that we choke with pollution. But what if there was actually a scientific basis behind an entity constituted by all life and non-life on Earth, capable of maintaining the biosphere?

In 1979 James Lovelock suggested just this, and he called his theoretical discovery Gaia. Since then, Gaia has been described in many different ways. There have been innumerable misconceptions and many accusations that there is insufficient evidence to call the concept a theory – some go as far as deeming it “unscientific.” Even if there isn’t sufficient evidence for Gaia to be considered by the scientific community, it’s still pretty damn interesting. The idea is that Gaia – this unimaginably complex chemical system – is capable of evolving, maintaining and self-regulating the conditions necessary for life on Earth.

Lovelock makes reference to self-regulating systems such as the salinity of the ocean, the concentration of oxygen in the atmosphere, self-sustaining ecosystems and global carbon-dioxide processing – all of which are maintained and regulated by the biological functions of living things (photosynthesis, for example), each of whom has a role analogous to organs in a hugely complex body.

This whole idea gets more interesting in Lovelock’s later work, where he described humans as a type of global infection; in the short time that we have been around, we’ve upset the chemical equilibrium ideal for life, causing mass-extinction. Just to make you feel better about yourself, according to Lovelock in his most recent work we are heading towards putting Gaia in a “coma-like state” that will take hundreds of thousands of years to recover from. “We are responsible and will suffer the consequences,” he says. Whether he is a brilliant scientist or a crazed fear monger, he made biologists stop and re-consider the way that living things interact on a global scale, and what role Homo sapiens should play in this.