800 – 700 million years ago

Year thirty-nine
Choaonoflagellates - the first animals?

Evolution of the first animals?

The animal kingdom must have evolved from the protist kingdom, which includes eukaryotes but doesn't include plants, fungi and animals — but nobody is certain when, how or from what. Very recently, however, it has been discovered that a microscopic, single celled protist called a 'collar flagellate' (or choanoflagellate) has a gene that goes by the grand name of 'receptor tyrosine kinase'. This gene controls other genes by telling them when to switch on and when to switch off. All animals have the gene and for the first time a non-animal has been discovered carrying it.

Because the gene is present in this protist, it is thought that all animals (including us!) must have evolved from something similar to it by about the Earth's 39th birthday (between 800 and 700 million years ago). Choanoflagellates are the nearest relative to animals so far discovered. However, the evolutionary steps taken to evolve from a protist to a multicelled animal, even one as simple as a sponge, remains unknown.

There are about 150 species of choanoflagellates known to be living in ponds and puddles today. They are microscopic, about five thousandths of a millimetre long, and swim using a hair-like tail (flagellum) in shallow water. They feed on bacteria that stick in its feeding 'collar'.


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