Darwin's theory of evolution explains how species of living things have changed over geological time. The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past, and the extinction of species continues to happen.
Adaptations - cold climates
Every organism has certain features or characteristics that allow it to live successfully in its habitat. These features are called adaptations, and we say that the organism is adapted to its habitat. Organisms living in different habitats need different adaptations.
The polar bear
Polar bears are well adapted for survival in the Arctic. They have: a white appearance, as camouflage from prey on the snow and ice thick layers of fat and fur, for insulation against the cold a small surface area to volume ratio, to minimise heat loss a greasy coat, which sheds water after swimming
Adaptations - hot climates
A cactus is adapted to life in a hot climate
Cacti are well adapted for survival in the desert. They have:
Stems that can store water.
Widespread root systems that can collect water from a large area.
In addition, cacti have spines instead of leaves. These minimise the surface area and so reduce water loss by transpiration. The spines also protect the cacti from animals that might eat them.
The camel is adapted to life in a hot climate
Camels live in deserts that are hot and dry during the day, but cold at night. They are well adapted for survival in the desert. Camels have:
Large, flat feet to spread their weight on the sand.
Thick fur on the top of the body for shade, and thin fur elsewhere to allow easy heat loss.
A large surface area to volume ratio to maximise heat loss.
The ability to go for a long time without water (they don't store water in their humps, but they lose very little through urination and sweating).
The ability to tolerate body temperatures up to 42°C.
Slit-like nostrils and two rows of eyelashes to help keep the sand out.
Animals and plants m ay have specific features that adapt them to their environment. These include barbs and spines, poisons and warning colours that deter predators and herbivores. Some harmless species may even resemble a poisonous or dangerous species to increase their chances of survival.
Charles Darwin (1809 - 1882)
Charles Darwin was an English naturalist. He studied variation in plants and animals during a five-year voyage around the world in the 19th century. He explained his ideas about evolution in On the Origin of Species, published in 1859.
Darwin's ideas caused a lot of controversy, and this continues to this day, because the ideas can be seen as conflicting with religious views about the creation of the world and creatures in it.
Darwin studied the wildlife on the Galápagos Islands (a group of islands on the equator, almost 1,000 km west of Ecuador). He noticed that the finches (songbirds) on the different islands there were fundamentally similar to each other, but showed wide variations in their size, beaks and claws from island to island. For example, their beaks were different depending on the local food source. Darwin concluded that, because the islands are so distant from the mainland, the finches that had arrived there in the past had changed over time.
Darwin's drawings of the different heads and beaks he found among the finches on the Galapagos Islands
Darwin studied hundreds more animal and plant species. After nearly 30 years of research, in 1858 he proposed his theory of evolution by natural selection.
Darwin's theory of evolution
The basic idea behind the theory of evolution is that all the different species have evolved from simple life forms. These simple life forms first developed more than three billion years ago (the Earth is about 4.5 billion years old). The timeline below shows