Henry Gee takes a look at why there are so few big animal species

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Published: Thursday, 06 June 2024 at 11:21 AM


There are several answers to why there are just a few huge animals, says Helen Gee.

The first is simply that the earliest organisms in any group tend to be small, and remain small – only a few evolve larger sizes.

The second is that large organisms take a lot of energy to maintain. So they require larger spaces to live in, and competition with other large animals will ensure that there are fewer of them.

The third is that larger creatures often run into problems of heat loss and support not suffered by smaller animals.

Yet a fourth is that larger animals tend to have fewer offspring, keeping populations small and survival precarious.

The fifth is that once they have become big, they need a huge standing stock of smaller creatures to feed on. It’s no wonder that the biggest creatures evolve in the sea – where the territories are vast, and problems of support and heat loss are minimised – and graze on enormous quantities of plankton that are further down the food-chain and easy to harvest.