Question: why are there so many different species of animals on earth?

  1. The emotional and human answer is – why not? Isn’t it great?

    But let’s be scientific. A species exists if it can. If the conditions are right – there is food, it’s the right temperature, it can produce babies and so on. The set of conditions that’s right for a species is called a “niche”. As the conditions change (e.g. as the world becomes warmer or colder) so will the species change. Elephants might grow hair and evolve into mammoths if we hit an ice age. The idea is that nothing is ever constant. Evolution is happening all around us and we don’t “see” it because it takes a long time.

    So the number of species you see around you is what the world can sustain. Maybe a few more or a few less might be possible, but basically we’re seeing a kind of steady state – the species we see all have “niches” and they’re fine. They are able to exploit their surroundings to live. There are relatively few places on the earth that can’t support life. The middle of the desert or right at the bottom of the ocean. But there are some extreme places that still do. Those animals are there because they’re able to be – they are able to live and have kids. That’s all you need. So a species exists because the animals are able to breed.

    We have to worry about any big disturbances – that might destroy where a species lives. Then we destroy its niche and we could wipe out the species. The world has existed for a lot longer than we have, and if we start losing a lot of species that might have bad unintended consequences, besides making the world a lot less interesting to live in. So cutting down forests and polluting rivers is a bad idea.


  2. Life first evolved in a warm soupy pool of water (or at the very depths of the ocean) somewhere on earth about 3.8 billion years ago. When that first type of life emerged, there was only one species. But as this life form multiplied, each individual was slightly different to the next one. This is because little errors can occur when DNA copies itself during cell division.

    Some of these life forms might have been different so that they could live in a slightly warmer temperature, so they might have moved to a warmer part of the pool (or the ocean). If these “warm” life forms lived away from the others for long enough, soon the two groups would be so different that they would be different species. This is the process of evolution by speciation (how different species form).

    This is just an example of speciation, but it happens with all different plants, animals and bacteria. If a group of animals can live in a different place or under different conditions to another group of animals in the same species, it means they don’t need to compete for space and food anymore. There are so many different places and conditions for animals to live in, and by evolution, they have changed into different species to be able to live in all these places


  3. Because there are so many different types of environment on Earth.

    In order to survive, each species needs to find a habitat which provides it with enough food, space and shelter to live and reproduce. There is a huge difference in the conditions of the ocean compared to the desert and a forest compared to a lake. Most species can survive in one of these environments but not another.

    If all the animals on Earth could live in a rainforest but nowhere else, then there would be all these other areas of the Earth without anyone to fight for territory or food, or to eat you. The animals in the rainforest, meanwhile, are all be competing with each other for survival, which does not lead to a pleasant and prosperous lifestyle. If one of these species developed a mutation (a change in the DNA) which allowed it to live outside the rainforest (eg. better lung capacity so it can live at high altitude, or longer fur so it can live in cold climates) then it could move to the new area. There would be nothing else eating its food or trying to eat it, and the species could get busy multiplying itself.

    This is basically what happened during evolution. We all started out as single-celled swamp-dwellers. After becoming multi-cellular fish type things which could live in these lakes, some of the fish-things mutated so they could live on land. Nothing else could live on land so they had a huge advantage. After a bit longer different types of land-dwellers would have emerged as more mutations occurred, allowing the different species to spread to new environments.
    After a very long time there would have been millions of species in millions of different environments which each was specially suited to. Many of these have since died as the conditions changed and the species was no longer successful, which leaves a gap for a new species to emerge.

    All of this is still happening now, but very slowly, so we couldn’t see it within our lifetime. Or even the lifetime of your entire traceable family tree. What we are seeing is the extinction of many species as their unique habitats are destroyed and they are not adapted to live anywhere else.