user471: The sutta below states that eyes, ears, nose, tongue, body and mind are old kamma.
Why are these called old kamma (purāṇakammā)?
Is it because of rebirth? Or could there be other reasons?
If rebirth is the only reason, then I feel that this explanation seems too simple.
From SN 35.146:

And what is old kamma?
The eye is old kamma. It should be seen as produced by choices and
intentions, as something to be felt.
The ear … nose … tongue … body … mind is old kamma. It should be seen
as produced by choices and intentions, as something to be felt.
This is called old kamma.
And what is new kamma?
The deeds you currently perform by way of body, speech, and mind.
This is called new kamma.

(I replaced "action" with "kamma")

user254: Piya Tan says, though I'm not sure this is clear,

“Old karma”
here refers to the six senses. The theme of “old karma” (purana,kamma) is applied to the body (synonymous with the six senses) in the (Kaya) Na Tumha Sutta (S 12.37/2:64 f), where the Anguttara Commentary explains that the body is not “old karma” but because it arises from old karma, it is referred to in
terms of its conditions. It is seen as “put together” (abhisankhata) since it is created by conditions. It is
“thought out” (abhisañcetayita) because it is based on volition (the will), rooted in volition. It is “to be
felt” (vedaniya) because it is basis for what is to be felt [ie the basis and object for feeling] (SA 2:70,
402).

Perhaps the idea is that people are born of (heir to) their kamma.
The summary on this page (I'm not sure who's the author, perhaps Ven Sujato) summarises this sutta as,

The six interior sense fields are not yours, but are old kamma, generated by choices in past lives. This is explained in terms of the four noble truths.


user8157: 
Why are these called old kamma (purāṇakammā)? Is it because of rebirth?

No. It appears to be the very opposite. The sutta appears to be dismissing the ordinary common view about 'rebirth', similar to AN 3.61, which dismisses the common view that happiness and suffering are due former kamma (pubbekata).
The suttas SN 35.136 & SN 12.37 literally say this kaya (group of aggregates) or these six sense organs are to be viewed as old kamma. These suttas do not say this kaya or sense organs are the result of old kamma. The group & sense organs themselves are old kamma.
Ordinarily, it is believed old kamma are actions a person personally does in the past. These suttas are actually ending this idea. These suttas are saying this present moment body & sense organs are to be viewed as old kamma and the noble practitioner should not trace further back to the past.
The above is particularly clear in SN 12.37, when it is said: "This kaya is not yours". Here, the ordinary common doctrine of personal old kamma is abolished.
In summary, SN 35.136 says three things:

The present moment sense organs are the oldest kamma, which is or can be something constructed & willed and which should be felt. This description is completely impersonal, namely, the sense organs are constructed from elements and from mother & father (per AN 9.15), the sense organs can be (wisely) subjected to the will if necessary and are to be felt without generating craving & self-view.

When these present moment sense organs are not merely felt, then new kamma is generated by craving, becoming & self-view via body, speech & mind; which is called 'new kamma'.

When the noble eightfold path is practised, no new kamma is created. Therefore, there is the cessation of generating or willing new kamma.


In summary, SN 35.136 & SN 12.37 appear to reject ordinary common ideas of old kamma from 'rebirth' & 'past lives'. It appears SN 35.136 & SN 12.37 are a supramundane (lokuttara) doctrine of 'old kamma'.

471: <p>The sutta below states that eyes, ears, nose, tongue, body and mind are old kamma.</p>
<p>Why are these called old kamma (<em>purāṇakammā</em>)?</p>
<p>Is it because of rebirth? Or could there be other reasons?</p>
<p>If rebirth is the only reason, then I feel that this explanation seems too simple.</p>
<p>From <a href="http://suttacentral.net/sn35.146/en/sujato" rel="nofollow noreferrer">SN 35.146</a>:</p>
<blockquote>
<p>And what is old kamma?</p>
<p>The eye is old kamma. It should be seen as produced by choices and
intentions, as something to be felt.</p>
<p>The ear … nose … tongue … body … mind is old kamma. It should be seen
as produced by choices and intentions, as something to be felt.</p>
<p>This is called old kamma.</p>
<p>And what is new kamma?</p>
<p>The deeds you currently perform by way of body, speech, and mind.</p>
<p>This is called new kamma.</p>
</blockquote>
<p>(I replaced &quot;action&quot; with &quot;kamma&quot;)</p>
 254: <p><a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/4.12-Nava-Purana-Kamma-S-s35.146-piya.pdf" rel="nofollow noreferrer">Piya Tan says</a>, though I'm not sure this is clear,</p>
<blockquote>
<p>“Old karma”
here refers to the six senses. The theme of “old karma” (<em>purana,kamma</em>) is applied to the body (synonymous with the six senses) in <strong>the (Kaya) Na Tumha Sutta</strong> (S 12.37/2:64 f), where the Anguttara Commentary explains that the body is not “old karma” but because it arises from old karma, it is referred to in
terms of its conditions. It is seen as “put together” (<em>abhisankhata</em>) since it is created by conditions. It is
“thought out” (<em>abhisañcetayita</em>) because it is based on volition (the will), rooted in volition. It is “to be
felt” (<em>vedaniya</em>) because it is basis for what is to be felt [ie the basis and object for feeling] (SA 2:70,
402).</p>
</blockquote>
<p>Perhaps the idea is that people are born of (heir to) their kamma.</p>
<p>The summary <a href="https://suttacentral.net/sn35" rel="nofollow noreferrer">on this page</a> (I'm not sure who's the author, perhaps Ven Sujato) summarises this sutta as,</p>
<blockquote>
<p>The six interior sense fields are not yours, but are old kamma, generated by choices in past lives. This is explained in terms of the four noble truths.</p>
</blockquote>
 8157: <blockquote>
<p>Why are these called old kamma (purāṇakammā)? Is it because of rebirth?</p>
</blockquote>
<p>No. It appears to be the very opposite. The sutta appears to be dismissing the ordinary common view about 'rebirth', similar to <a href="https://suttacentral.net/an3.61/en/bodhi" rel="nofollow noreferrer">AN 3.61</a>, which dismisses the common view that happiness and suffering are due former kamma (pubbekata).</p>
<p>The suttas SN 35.136 &amp; SN 12.37 literally say this kaya (group of aggregates) or these six sense organs are to be viewed as old kamma. These suttas do not say this kaya or sense organs are the result of old kamma. The group &amp; sense organs themselves are old kamma.</p>
<p>Ordinarily, it is believed old kamma are actions a person personally does in the past. These suttas are actually ending this idea. These suttas are saying this present moment body &amp; sense organs are to be viewed as old kamma and the noble practitioner should not trace further back to the past.</p>
<p>The above is particularly clear in SN 12.37, when it is said: &quot;<em>This kaya is not yours</em>&quot;. Here, the ordinary common doctrine of personal old kamma is abolished.</p>
<p>In summary, SN 35.136 says three things:</p>
<ol>
<li><p>The present moment sense organs are the oldest kamma, which is or can be something constructed &amp; willed and which should be felt. This description is completely impersonal, namely, the sense organs are constructed from elements and from mother &amp; father (per <a href="https://suttacentral.net/an9.15/en/thanissaro" rel="nofollow noreferrer">AN 9.15</a>), the sense organs can be (wisely) subjected to the will if necessary and are to be felt without generating craving &amp; self-view.</p>
</li>
<li><p>When these present moment sense organs are not merely felt, then new kamma is generated by craving, becoming &amp; self-view via body, speech &amp; mind; which is called 'new kamma'.</p>
</li>
<li><p>When the noble eightfold path is practised, no new kamma is created. Therefore, there is the cessation of generating or willing new kamma.</p>
</li>
</ol>
<p>In summary, SN 35.136 &amp; SN 12.37 appear to reject ordinary common ideas of old kamma from 'rebirth' &amp; 'past lives'. It appears SN 35.136 &amp; SN 12.37 are a supramundane (<em>lokuttara</em>) doctrine of 'old kamma'.</p>
