Wikijunior:Biology/Creatures

Creatures
Many different creatures live on earth: plants, insects, birds, fish, bacteria, humans and many more. They have many differences and similarities.

Are living beings related to each other?
''According to the theory of evolution, all living beings on earth are related to each other. ''

We humans are therefore related to monkeys, cows and apple trees, but also to mosquitoes and bacteria. All living organisms on earth today share common ancestors.

Tree of life
In 1879, the biologist Ernst Haeckel drew a family tree of living things inspired by the family trees of noble families. At the roots are the unicellular organisms, from which all higher living beings descend, with humans at the top. Scientists are aware that scientific statements can be wrong and therefore look for errors. They found errors in Haeckel's picture. So, the birds are drawn in the wrong place.

Modern family trees are much more complex. Humans are now on a par with other living organisms. On the left of the picture are the mammals, next to them are the birds. One of the lines denotes the humans. Extinct creatures such as dinosaurs are not shown here. Even the modern family trees are probably wrong. Viruses can transfer genes between different organisms and protozoa can exchange genes with other protozoa. There are many unanswered questions, especially in the case of unicellular organisms. There is still much to explore for future biologists.