Scientists believe there are around nine million different species of organisms on planet Earth, although only 1.3 million have been discovered. These organisms vary massively; each species has different characteristics based on their environment and what they need to survive. Life exists in almost every corner of the world, from the polar regions at the top and bottom of the Earth to the hot, arid deserts in the middle. The only places scientists believe life doesn’t exist are inside volcanoes and inside hydrothermal vents where the temperature is too high.
In 1831, Charles Darwin left England on the HMS Beagle on a five-year voyage around the world and, as the ship's scientist, he studied the natural world he encountered. On his journey, he observed that there was a large variation in the living things he saw, and he began to wonder why that was.
Darwin reached the Galapagos Islands in 1835. In the Galapagos, he noticed that animals varied from island to island. In particular he noticed a family of birds whose beak was a different shape depending on which island they lived on. Darwin linked the shape of the bird’s beak with the type of food that made up the majority of the birds’ diets. The shape of the birds’ beaks is an example of an adaptation, something that helps a living thing survive or reproduce more easily. This led him to develop the theory of evolution by natural selection, one of the most important theories in biology.
Darwin used these observations and came to the conclusion that the reason the organisms were different was due to gradual changes over time. The organisms that had advantageous adaptations had a high chance of surviving and reproducing, meaning they had a higher chance of passing their genes onto the next generation. Those organisms that did not possess these adaptations had a lower chance of survival and reproduction, therefore a higher chance of dying before they could pass on their genes. Over many generations, organisms evolved to be better suited to their environment. While still technically a ‘theory’, Darwin’s ideas have been accepted by the scientific community as the reason for varied life on Earth.
In order for organisms to survive, they need to have adaptations which give them an advantage when living in their environment. Every animal, plant, bacterium, fungus, archaeon, and protist has characteristics that allow it to be successful in surviving in its habitat. These adaptations can be categorized into behavioral, structural, or physiological. Behavioral adaptations can be inherited or learned. Behavioral adaptations include communication and swarming. An example of a physiological adaptation is the ability to make venom. Structural adaptations are ways the organism's body or structure is adapted to help the organism survive or reproduce. An example of a structural adaptation could be the streamlined shape of a dolphin that allows it to move through the water more easily.
Organisms compete with each other for resources like water, food, sunlight,or space. They also compete with each other to reproduce. Organisms that are well adapted will have a higher chance of getting the needed resources. If organisms are unsuccessful and are unable to move to another habitat, they will not survive.