rob faraone asked:
Insects seem to be SO different from other species that I find it hard to imagine they evolved from the sea. There is talk and evidence of Earth being seeded by asteroids and comets etc. Is it feasible that insects are direct result of alien life forms rather than of evolution from the sea?
We put this question to Georgia Mills and Zephyr Penoyre...
Georgia - Insects are very strange-looking sometimes. But if you look across the whole animal kingdom, there are some really, really weird ones. Look up water bears, if you get a minute, they're some of the strangest creatures you'll ever see. There's also…
Chris - What's one of those?
Georgia - They're these tiny little creatures that can basically just survive anything. they look like something from a studio Ghibli film. They're like really, really creepy tiny things. but insects did almost certainly are in the same tree of life as all other animals. The reason we know this is from things like DNA sequencing and also from the fossil record. Insect fossils are very hard to come by but there are a few that look like transitions between insects and their close relatives, the other arthropods. And did insects come from a comet? Well, like you mentioned Zephyr, there's the theory that all life came from a comet. This is panspermia. This is an interesting debate but if it did happen like this, it’s likely that all life came this way. If a comet arrive now with some exciting new microbes on it, it’s likely that the current biology of the planet which is gobble it up.
Chris - Zephyr…
Zephyr - They actually sent some tardigrades - water bears - up into space!, not really planning to get them back down, and they got them back down and found that they were fine! They'd survived the vacuum of freezing cold space absolutely fine!
Humans, insects, and all plants share the same basic cell structure, including a nucleus, DNA, RNA, proteins, amino acids, and etc. The major exception is that plants have chloroplasts that animals and insects lack.
The oft-repeated suggestion of alien seeding doesn't answer the question of how anything evolved: it just adds another question of where and when. Since we have no reason to suspect that chemistry is any different elsewhere in the universe (otherwise our alien visitors wouldn't survive and thrive on this planet), the how question must be answered within the known conditions of Earth. alancalverd, Wed, 18th Dec 2013