lpetrich
Contributor
Grammars Across Time Analyzed (GATA): a dataset of 52 languages | Scientific Data -- all of them langs without long literary traditions. Did the authors try to avoid literary traditions as linguistic interference?
Lexibank, a public repository of standardized wordlists with computed phonological and lexical features | Scientific Data
The time and place of origin of South Caucasian languages: insights into past human societies, ecosystems and human population genetics | Scientific Reports - the Kartvelian ones, including Eurasian Georgian
They used
They found
 Colchis is at the east end of the Black Sea.
 Colchis is at the east end of the Black Sea.
				
			Lexibank, a public repository of standardized wordlists with computed phonological and lexical features | Scientific Data
The time and place of origin of South Caucasian languages: insights into past human societies, ecosystems and human population genetics | Scientific Reports - the Kartvelian ones, including Eurasian Georgian
They used
- the past distribution ranges of wildlife elements whose names can be traced back to proto-Kartvelian roots
- the distribution ranges of past cultures
- the genetic variations of past and extant human populations.
They found
- Zan: 1,200 BP - Laz, Megrelian
- Karto-Zan: 2,617 BP - Georgian, Zan
- Proto-Kartvelian: 7,641 BP - Svan, Karto-Zan
Our analyses place the Kartvelian Urheimat in an area that largely intersects the Colchis glacial refugium in the South Caucasus. The divergence of Kartvelian languages is strongly associated with differences in the rate of technological expansions in relation to landscape heterogeneity, as well as the emergence of state-run communities. Neolithic societies could not colonize dense forests, whereas Copper Age societies made limited progress in this regard, but not to the same degree of success achieved by Bronze and Iron Age societies.
 Colchis is at the east end of the Black Sea.
 Colchis is at the east end of the Black Sea.According to the mean split dates estimated by the phylogenetic model, the divergence between Svan and Karto-Zan occurred prior to or at the beginning of the introduction of metallurgy in the study area, while Georgian and Zan diverged in the Iron Age, specifically during the Urartian period.
 
	 
 
		 
					
				 
 
		 Although if you asked me to name the living language that's closest to PIE, I'd probably go for Lithuanian (not before telling you it's a rather meaningless question without some context what kind of feature you're interested in). Latvian is also fairly conservative structurally I believe, but their lexicon has rin amok with taboo replacements. You know how Germanic, Slavic and Baltic have lost their inherited IE  word for "bear" (cf Greek "arctos", Latin "ursus", replacing it with euphemisms like "Brown one", or "Honey knower" ("medvjed"), or whatever it is the Balts use, because calling his name was apparently considered sacriligeous, or bad luck? Well, Latvian does that same thing for "son" and "sister"!
 Although if you asked me to name the living language that's closest to PIE, I'd probably go for Lithuanian (not before telling you it's a rather meaningless question without some context what kind of feature you're interested in). Latvian is also fairly conservative structurally I believe, but their lexicon has rin amok with taboo replacements. You know how Germanic, Slavic and Baltic have lost their inherited IE  word for "bear" (cf Greek "arctos", Latin "ursus", replacing it with euphemisms like "Brown one", or "Honey knower" ("medvjed"), or whatever it is the Balts use, because calling his name was apparently considered sacriligeous, or bad luck? Well, Latvian does that same thing for "son" and "sister"!