Evolution is often mistakenly depicted as linear in popular culture. One main feature of this depiction inpopularculture, but evenin science popularisation, is that some ocean-dwelling animal sheds its scales and fins and crawls onto land.Of course, this showcases onlyoneancestral lineage foronespecific species (Homo sapiens). My question is:Where else did life evolve out of water onto land?Intuitively, this seems like a huge leap to take (adapting to a fundamentally alien environment) but it still must have happend several times (separately at least for plants, insects and chordates, since their respective most recent common ancestor is sea-dwelling). In fact, the more I think of it the more examples I find.

Dear Ali,

This is a great question. You have obviously spotted the major groups, insects, chordates and plants, but there are, as you suggest many more. I don't have a 'number' answer to give you, but it is indeed many many times. Life started in the oceans more than 3.5 billion years ago, and by 540 million years ago, all/most of the major animal Phyla were present. Just thinking about animals, we have beautiful fossil deposits from Canada to China that show the amazing diversification of animals at this time. We have annelid worms, molluscs, you name it. All of these groups originated in the seas. It follows that if we find them in terrestrial environments either as fossils, or alive today, they must have made that transition to land. How many times the land has been invaded by animals is hard to tell. It is fair to say that a minimum number must be the number of Phyla that we find on land. However, it isn't necessarily that simple. There are some groups that we think of as being aquatic. An example of this would be the crustaceans. What we forget is the woodlice, or pill bugs, are crustaceans. So, it is fair to say that Arthropoda (a single Phylum) has invaded the land on multiple occasions, giving us the terrestrial Classes of insects, arachnids (spiders and scorpions), myriapods (centipedes and millipedes) and crustaceans. 1 Phylum, 4 (at least) separate invasions. This is a very interesting question. I will try and get you a more complete answer, so keep checking back.