
Three-Domain System - hhs
https://en.wikipedia.org/wiki/Three-domain_system
======
Fnoord
In elementary school I got taught about six-kingdom system, so I am surprised
there's been an update in 1990. To which domain do viruses belong? Still an
odd exception?

~~~
saagarjha
I was taught the three domain system, although this was a couple decades after
the model. Viruses don’t fit in because they’re not alive.

~~~
abjKT26nO8
According to Wikipedia[1]:

 _> Scientific opinions differ on whether viruses are a form of life, or
organic structures that interact with living organisms._

And:

 _> Viruses are now recognised as ancient and as having origins that pre-date
the divergence of life into the three domains._

[1]:
[https://en.wikipedia.org/wiki/Virus](https://en.wikipedia.org/wiki/Virus)

~~~
s_kilk
I was taught that viruses are weird little machines, similar but unrelated to
the things we recognise as alive. Interesting that there's difference of
opinion on the matter.

Edit: here's a question for the room; if viruses are unrelated to the rest of
"life", but are endogenous to the earth, are they alien?

~~~
antonvs
It's an overstatement to say that viruses are "unrelated to the rest of life".
They have RNA or even DNA, which almost certainly makes them related.

If we found a living organism which didn't have RNA or DNA, that would be a
good candidate for an alien. It would help if we found it on another planet
though.

~~~
s_kilk
Thanks for the clarification, that makes sense.

------
ncmncm
Kudos for prominent feature of the dissenting view.

I thought it was the mainstream. Didn't we establish that eukaryotes are
descended from archaea that engulfed rickettsia or cyanobacteria, presumably
after inventing nuclei? It seems presumptuous to claim a domain just for that,
successful as it may have been.

------
whytaka
Ignorant to even the basics of biology, I happily traversed the wikipedia
rabbit hole and learned a ton thanks to this link.

Thanks!

------
saagarjha
The Wikipedia article is sadly quite light on details for a system that
underpins modern taxonomy…

~~~
duskwuff
There's a more detailed article at:

[https://en.wikipedia.org/wiki/Kingdom_(biology)](https://en.wikipedia.org/wiki/Kingdom_\(biology\))

------
hoseja
Seems pretty pointless when you take horizontal gene transfer into account.

~~~
dspillett
I've always thought that as more of a mutation source rather than a more
direct driver for evolution and therefore our artificial classification
divides.

Mutations happen constantly: transcription error, radiation, and yes
horizontal transfer, but many other factors decide if the mutation sticks or
not. But gene transfer doesn't break a hierarchical classification system much
more than solar radiation does.

------
ur-whale
Is this classification arbitrary, or does it try to actually reflect some sort
of genetic ancestry tree?

Also: does it have any kind of predictive power or does it just scratch the
itch of putting things in little separate boxes for its own sake ?

