My father recently pointed me to the research work of Dr. Susumu Ohno, a Japanese linguist who studied ancient Japanese as well as ancient Tamil (a language spoken in South India).
Dr. Ohno (in a paper titled “The Genealogy of the Japanese Language”) made a number of interesting observations about phonological similarities and the existence of cognates (similar-sounding words) in the some forms of both languages.
For example, he noted that the in some dialects of Japanese, the words for “father”, “mother”, “elder brother” and “elder sister” are similar to the words used in Tamil.
In some Honshu and Ryukyu dialects of Japanese, the words for father, mother, elder brother and elder sister are “accha”, “aaya”, “annyaa” and “anne”. Ohno argues that these words resemble the words “acchan”, “aaya”, “anna” and “annai” in Tamil.
I found that his observations supported some arguments that I had made in a blog entry in 2010 (I’d attempted to draw a 3-way comparison between Japanese, Tamil and Australian aboriginal languages).
He proposes a theory that in early Japanese, there were no e and o sounds – that these sounds were replacements for ai or ia and ua.
I quote:
The vowels in group B are believed to have resulted from the merging of two vowels, as follows: ia>e, ai>e, ui>i, oi>i, ua>o
Though I don’t have a reference, I am told that T. P. Meenakshi Sundaram made an almost identical assertion in the case of Tamil.
You also see some evidence of such a transformation in the Tulu word “yan-ku” (to me). The corresponding word in Tamil is “en-akku”. The correspondence makes you think that sometime in the past, they used to say “yan-akku” in Tamil instead of “en-akku”.
You see a similar correspondence in Kannada. The Kannada word for why can be written and pronounced as “yaake” or as “eke”. So “ia” seems to be replaceable with “e” there.
Similarly in Tamil, the word “evan” (who) can also be pronounced (colloquially) as “yaveng”.
So, if both ancient Tamil and Japanese used just a, i and u sounds, their phonetics begins to resemble that of Australian languages like Dyirbal.
Regarding consonants, Ohno notes the following correspondences:
Japanese
Consonants at head of word
k-, s-, t-, n-, F-, m-, y-, wConsonants mid-word
-k- , -s-, -t-, -n-, -F-, -m-, -y-, -w-,
-r-, -ng-, -nz-, -nd-, -nbTamil
Consonants at head of word
k-, c-, t-, n-‘ n-, p-, m-, y-, vConsonants mid-word
-k- , -c-, -t-, -n-, -p-, -m-, -y-, -v-,
-t- , -n-, -r-, -1-, -r-, -1-, -r-,
-nt- -nc, , -nt-, -mp-
Unfortunately, I don’t know Dyirbal or any Australian language. So, I can’t check if these rules apply to them as well. I can’t wait to get hold of a linguistic analysis of Dyirbal by an Indian or Japanese linguist.
Aiaioo Labs Blog 
Interesting. While Tamil does have “yAn” (யான்) for “I” attested in the literature, I am not aware of “yAnakku” (யானக்கு) even in ancient Tamil. But children make up words like that when they learn Tamil. They understand “nAn” (நான்) to mean “I” in modern Tamil and they would say “nAnukku” (நானுக்கு) to mean “to me.”
Literary Tamil does have yAvan யாவன் as a synonym for evan (எவன்).
Still these alone aren’t sufficient for historical linguistics. The connection between native Australian languages and Tamil have been speculated but it is difficult to connect the two as the earliest sample of Tamil we have is already a highly sophisticated literary language which was several thousand years removed from the proto languages of the native Australians.
It is also true that to this day, Tamil and the Dravidian languages are isolates without any firm connection to any language families outside of Indian subcontinent. The probably connection with Japanese is interesting but remains speculative.
Tamil, Malayalam, Telugu, Thulu, Kannada and Brahui are languages belonging to DRAVIDA family. Members of this family are not confined to South India. They are in North India as well as outside India.. Brahui is spoken in Pakistan (Baluchistan), Afghanistan and Iran.. Family of Japanese language is Ural-Altaic. The Similarity between Tamil and Japanese is because of the fact that both Dravida .family an d Ural-Altaic family are related. They are members of the DURALJAN superfamily of languages.
– Dr K Sugathan
@Manivannan: It is not yAnakku” (யானக்கு). it is en-akku(எனக்கு)
Yaan + kku becomes enakku because the yaan has another form ean.The Yaan or Naan of Tamil has become Njaan in Malayalam, an younger sister of Tamil. In Malayalam language Njaan which means I, or naan or yaan changes to the form Aen when it takes the post-positions kku,e, aal, ude etc. Njaan + kku becomes Enikku. ( The Enakku of Tamil has become Enikku in Malayalam.). Njaan + udaya (meaning my) becomes Ennudaya, Ennude, Ente. In Sanskrit Aham is I, but it takes the “M’ form. Various case forms are mama, maam etc. In English the pronoun I takes the “M’ form as me,my,mine etc. Wonderful similarity.