Over a century ago, when a 30-year-old Edwin Hubble was offered a job at the Mount Wilson Observatory outside Los Angeles, he was given an opportunity that must have made all his fellow astronomers exceedingly jealous: to handle the most powerful telescope then built. One night, when he directed it towards a hazy patch of sky called the Andromeda Nebula, he made an astonishing discovery – what most people had assumed to be gas and dust was, in fact, an entirely distinct galaxy which Hubble estimated to be almost a million light years away from us. Until then, astronomers thought that everything we could see belonged to our own Milky Way, which was synonymous with the known universe.

Hubble’s discovery built on the knowledge and dedicated work of many others before him, who had been equally keen to explain and measure what they saw in the skies. Some of them remain unsung heroes of science, like Henrietta Leavitt, whose mere gender excluded her from all due recognition among the exclusively male astronomers at the Harvard College Observatory where she started work in 1893. It was Leavitt who discovered a way to confidently measure the distance to stellar objects far away – an insight which allowed Hubble’s estimation of the observable universe. In the years that followed, Hubble went on to map dozens of other galaxies outside our own.

In 1990, space exploration was boosted again by a space telescope which, perhaps not surprisingly, was named in Hubble’s honor. It showed us in clear, colorful images that the universe is immensely larger and more astonishing than anyone could ever have imagined. Today, astronomists think there are a staggering 200 billion galaxies and one billion trillion stars in the observable universe. To put that in perspective, if every star was the size of a pea, you could cover the entire Earth with a two-kilometer-thick layer of peas. We have no idea how many planets there are, but since the existence of the first exoplanet (a planet that orbits a star outside our solar system) was confirmed in 1995, we have found over 4,300 and counting.

On planet Earth, biodiversity – the variety of life – is our ‘hidden universe.’ Its components are far more abundant, numerous, complex and interwoven than most people may realize. In Africa, our ancestors began to explore biodiversity very early on in our evolutionary history and were guided by the most basic needs of food, shelter and comfort. For hundreds of thousands of years, they tasted most things they came across. They used their senses to explore the plants growing around them and observed what other animals ate. They discovered that some plants had edible roots, but the leaves would make them sick, some plants produced sweet juicy fruits while others were bitter, and some plants were best avoided at all costs. They gradually increased their diet to include many different parts of plants, fungi, mammals, birds, fish, insects and spiders. They learned which trees provided the best wood for making fires, which animals had the best fur for keeping them warm, and which fruits were most delicious.

As our human ancestors left eastern Africa and reached other parts of the world, they made new discoveries. On every continent, the exploration of nature began immediately after their arrival. There was often abundant prey, but they had to learn how to hunt it, or satisfy themselves by scavenging on carcasses. They gathered many different sorts of nuts and berries. In some places, animals were easier to catch but fewer in number, like in the Indonesian island of Flores. The island is so tiny and food resources so limited that, when our human relatives arrived there about a million years ago, natural selection consistently benefited small individuals, leading to the evolution of a separate species. An adult Homo floresiensis was only about a meter tall (3.3 feet), which is shorter than most humans with dwarfism today and about the same size as the island’s own species of dwarf elephant. In the Levant, another relative of ours, Homo erectus – which inhabited many parts of Africa and Eurasia for some 1.5 million years – relied on elephants, hippos, rhinos and other large animals as a source of a fat-rich diet.

As the brain size and cognitive abilities of our ancestors increased, they became increasingly better at developing tools for hunting and processing plants and animals. The development of thousands of local languages allowed them to communicate what they had discovered about the species around them and their uses. In China, archaeological evidence for herbal medicines began some 8,000 years ago. By 4,000 years ago, the Sumerians had left written accounts demonstrating their use of plants like cumin, mint and liquorice. There’s scientific debate on this topic, so it may be wisest not to include this as it is only tangential information.

While most information associated with species was passed around by word of mouth, the Greeks attempted to synthesize all knowledge available at the time. In the fourth century BCE, Aristotle wrote down everything that was known to him about animals. Shortly after that, his apprentice Theophrastus did the same, but focusing on plants. Knowledge about species continued to grow, and discoveries piled up. Farmers experimented with ever more species, which increased the nutritional value of our diet and the range of climates and regions in which we could grow food. Traditional Chinese medicine – characterized by the prescription of many different plants and animals to treat all sorts of ailments – became increasingly popular across much of eastern Asia.

However, by the time western societies entered the Scientific Revolution of the seventeenth and eighteenth centuries, things had got messy. No comprehensive summaries of plant and animal knowledge had been written in Europe for almost 2,000 years, and people from different countries struggled to communicate their knowledge about species. Even when they could use the same language – usually Latin, among scientists – they didn’t have a standardized way to name species. The dog rose – a common wild rose in Europe, whose fruits can be turned into a nutritious soup if you dry them and remove the hairy seeds – would be called Rosa sylvestris inodora seu canina by one person and Rosa sylvestris alba cum rubore, folio glabro by another. Not only was it a burden to learn all the different names a species could have, but also those names were often long and awkward. Misunderstandings were common and could be disastrous. In the carrot family, for instance, some of our best foods and spices – including carrots, celery, anise, coriander and parsley – could easily be confused with some of the most poisonous wild plants known, due to their similar flowers and leaves.

The person who brought order to chaos was the Swedish naturalist Carl Linnaeus. As a child, growing up in the countryside among farm animals and a rich wild flora, Linnaeus was already collecting and asking his father for help in naming everything he found – from flowers to insects and fish. He traveled the country on horseback, gathering specimens and detailing notes of every species he saw. In 1735, aged just 28, Linnaeus published the first edition of his Systema Naturæ (‘System of Nature’), where he proposed a strictly hierarchical classification of all living things. Like the traditional Russian Matryoshka dolls, each category was contained within slightly bigger ones: species were grouped into genera, which were grouped into families, orders, classes and, finally, kingdoms. Applying this classification system, he was the first scientist to document, for instance, that whales and dolphins are more closely related to land mammals such as pigs, than to fish like tuna, despite their very different appearance and behavior. Perhaps most importantly of all, Linnaeus proposed that every species ought to be given a single binary name: Felis catus for the domestic cat, Falco peregrinus for the peregrine falcon, and Rosa canina for the rose mentioned above. His naming and classification system was so simple and useful that it came as a relief to many, and, with many refinements, it has survived to this day.