Viewing a single comment thread. View all comments

bruceleroy99 OP t1_izapkus wrote

Reply to comment by jellyfixh in Have living things always had an immune system? How did they survive / evolve to deal with diseases, and how does that compare to modern immune systems? by bruceleroy99

oh, ha, wasn't expecting that! I assumed viruses wouldn't be a thing until it was more "valuable", as it were, to attack another life - seems almost counterintuitive that it basically started off as a single cell attacking another single cell (this coming from someone that did very poorly in bio class XD). I would've thought it would be less efficient to attack another cell instead of just growing oneself.

18

BetterLivingThru t1_izauhtd wrote

Viruses actually are not other cells, they're far, far smaller and simpler then cells, essentially just some RNA or DNA and enough protein to get into the cell and get to work, so it is very worth it for them to infect even tiny single celled organisms, since they are thousands of times larger than viruses, and viruses simply cannot reproduce on their own, unlike bacteria. There are, however, also bacteria that do infect and parasitize other bacteria, growing inside them and using their energy to grow and reproduce, like bdellovibrio bacteriovorus. There are also predatory single celled organisms, that eat other single celled organisms. Single celled organisms come in all kinds of sizes, and fill all sorts of niches in their ecology. Just as a leech cannot take energy and reproduce by photosynthesizing or by eating grass and has to be a parasite, so to do most of these organisms have no choice but to fill the roles they have adapted to fill.

50

bruceleroy99 OP t1_izb8uig wrote

ooooh got it, that makes a lot more sense! extremely informative, too, thanks! I assume it isn't known at what point viruses / bacteria developed alongside everything? e.g. if single-celled organisms are 1000s x bigger than viruses, how big were things when viruses first started forming?

9

clocks212 t1_izbtz5k wrote

It’s unknown whether cellular life came before viruses or if cellular life evolved from viruses.

10

mcr1974 t1_izc29sd wrote

but what would have viruses attacked?

2

the_quark t1_izc59cy wrote

They might have started simply as self-replicating sets of chemicals in the early ocean. At this point though we've only been able to speculate about their (and life's) ultimate direct origin.

8

Octavus t1_izd243f wrote

There are also viroids which are even simpler than viruses. They are simply a circular strand of RNA, that is it. However they are still able to infect plants, use their cellular machinery to create more copies, and spread.

4

astral_melum t1_izbcbgo wrote

Adaptive immunity, where an organism uses a host of specialized blood cells to defend against pathogens is (as far as we've been able to figure out) an evolutionary phenomenon of vertebrate animals. Multicellular animals also have innate immunity that likely evolved from unicellular defenses against infection by viruses and against predation. Some of the adaptive immunity blood cells (macrophages) look and act like single-celled amoebae in how they chase after and engulf their food. If you're not familiar with Kurzgesagt - In A Nutshell, they have a wonderful series of videos on this (and many other) science topics. I assign these videos to my entry-level college biology students to help them understand immunity.

edited for formatting

10

scarabic t1_izd8pr8 wrote

The same answer goes all the way down really. There’s not a single chemical process or pathway anywhere in your entire metabolism that wasn’t invented in bacteria before multicellular life came about. Even photosynthesis originated in bacteria, long before there were plants.

2