In several Indo-European languages the verb that denotes possession (to have) is also used to construct verb tenses.
I have seen ... I have a dog. (English)
Am văzut ... Am un câine. (Romanian, am = I have. Note: this past tense in Romanian doesn't correspond directly to present perfect in English, but it's still an example of a tense formed with the equivalent to "to have".)
Έχω δει ... Έχω ένα σκύλο. (Greek, έχω = I have)
(And many others, such as Italian, French, Norwegian, etc. All sentences above have the same meaning, except for the noted difference in the precise tense.)
Since all of these languages are related, it is not that surprising that in all of them the verb to have shares these functions. I used to think that this is just an accidental idiosyncrasy of Indo-European languages, and there's no fundamental reason why it should be so.
But it turns out that Chinese (an unrelated language) is also like this:
我没(有)看到 ... 我有 一只狗。 (有 yǒu = have, 没有 méi yǒu = haven't)
Wǒ méi (yǒu) kàn dào... Wǒ yǒu yī zhi gǒu. (Meaning: I haven't seen ... I have a dog.)
Hungarian (my mother tongue) doesn't have anything like this (in fact it doesn't even have a verb for possession), so this double function of have is surprising and counterintuitive to me.
Question: Is there any fundamental reason why several unrelated languages would all use to have in these two seemingly separate and unrelated roles?