While the Law of clean and unclean meats (or animals) was officially first commanded by God to Moses, Aaron, and Israel; the truth is clean and unclean meats/animals were known (at least to a certain extent) long before Moses (and even Israel/Jacob) was ever born.
The knowledge of clean and unclean animals goes back to at least Noah (and possibly his generation):
It’s clear from the Bible that Noah knew about the concept of clean and unclean animals (thus meats) very well and how to identify a clean and unclean animal:
This has to be the case because when God begins telling him his plan to flood the world and commanding Noah to build an ark to escape the flood; God specifically commands him to get 7 pairs (that is 7 males and 7 females) of all clean animals but only 1 pair (that is 1 male and 1 female) of all unclean animals:
Genesis 7:1-3
“The Lord then said to Noah, ‘…Take with you seven pairs of every kind of clean animal, a male and its mate, and one pair of every kind of unclean animal, a male and its mate,…’”
Obviously, Noah was expected to already know what a clean and unclean animal was because God wouldn’t order a human to do something that they did not understand: and Noah is not recorded asking God what a clean and unclean animal was: therefore, Noah very likely already knew what a clean and unclean animal was and was able to bring 7x more clean animals than unclean ones according to God’s command.
Also, When God stopped the flood and the animals and Noah and his family were allowed to leave the ark, Noah then built an alter to God and took one of every clean land animal and birds and sacrificed them to God:
Genesis 7:20
“Then Noah built an altar to the Lord and, taking some of all the clean animals and clean birds, he sacrificed burnt offerings on it.”
This confirmed Noah absolutely knew which land and flying animals were considered clean (and those who were unclean) and was able to pick them out as a proper sacrifice to God (signifying unclean animals were most likely unfit to sacrifice to God).
This sacrifice of every type of clean animal pleased God so much that he swore he would never try to destroy all humans and (land) animals:
Genesis 7:21
“The Lord smelled the pleasing aroma and said in his heart: ‘Never again will I curse the ground because of humans,…And never again will I destroy all living creatures,…’”
While this pretty much confirms ,by at least Noah’s generation, clean and unclean animals were known (at least by Noah and his family at least) this does not necessarily mean God just started revealing clean and unclean animals to Noah or even only that generation, but God could have taught the earlier generations of Adamites (possibly even Adam and Eve themselves) the knowledge of clean and unclean animals; even though before Noah there is no direct evidence Humans knew about the clean and unclean animals but there is an absence of unclean animals pre-humans seemed to have raised and most likely sacrificed to God (like Noah):
Abel (the son of Adam) shepherded flocks of sheep or/and goats (both considered clean animals) instead of a pin of pigs (considered an unclean animal) in fact, Able is the first known shepherd recorded and sacrificed his firstborn sheep/goat of his flock to God (in comparison to the firstborn piglet of his pin):
Genesis 4:2-4
“...Now Abel kept flocks…And Abel also brought an offering—…the firstborn of his flock.[1]”
Jabal’s descendants (which was in turn a descendant of Cain: so, they would be Jabalite Cainites) raised herds of cattle (or cows/oxen: considered clean animals), instead of raising herds of horses or nests of rabbits (both considered unclean animals):
Genesis 4:20
“...Jabal; he was the father of those who live in tents and raise livestock.[2]”
Now, this is not definite proof that pre-flood Adamites/humans did not also raise unclean animals as well as clean, neither is it proof that they knew about clean and unclean animals, but the lack of mentioning of unclean animals (as defined later in the specific list God gave to Moses and Aaron concerning clean and unclean animals/meats) hints of the possibility that the Adamite humans before the flood might have known about clean and unclean animals and this is why they seemed to have only raised sheep/goats and cows/other clean livestock (this would also explain how Noah knew about clean and unclean animals when God just began speaking to him without any further instruction known before).
But regardless if the humans of the pre-flood knew about clean and unclean animals, definitely Noah’s children/descendants would have originally known about clean and unclean animals. Noah would have naturally told his children (and his/their wives) about the clean and unclean animals and they (if they were not rebellious) would have also taught their children about the knowledge of clean and unclean animals (wherever they actually kept this knowledge and passed it down to their children is another story) because sadly it seems along with the majority of the Noahic covenant, many of Noah’s descendant (Noahites) largely forgot the knowledge of clean and unclean animals/meats except possibly a few unclean animals:
But for the most part, Noahites hunted and ate (and also sacrificed) any animal they caught and though of them as generally the same (there was no concept of clean and unclean animals/meats really in any of these civilizations even if they remembered one or two unclean/clean animals for some reason) so it seems the knowledge of clean and unclean animals originally known by Noahites was pretty much lost:
At least until the time God called Abraham and made his covenant with him:
Now it’s not directly stated that God taught Abraham about the knowledge of clean and unclean animals/meats, however there are strong hints that Abraham (wherever God taught him the knowledge of Clean and unclean animals, or he was one of the last few Noahites left that still knew about clean and unclean meats) knew there was difference between clean and unclean animals just like his ancestor Noah:
Abraham possessed many herds of cows, goats, and sheep (all clean animals) (instead of pigs, horses, and/or rabbits):
Genesis 13:5
“...Now…Abram,...had flocks and herds…”
While Abraham was said to have a good bit of Sheep, cows, and goats, this was not abnormal for Hebrews at this time: because Hebrew people (especially the Hebrews in Abraham’s extended family) were commonly shepherds often keeping and tending sheep and goats in large herds:
This is made pretty clear the strong connection to these specific Hebrew people (if not all the other descendants of Eber/Hebrews at this time) as being herdsmen as their traditional job when Pharaoh (an Egyptian: which was most likely an Mizramic Hamite [A Noahite descended from his son Ham and from Ham's son Mizraim: The patriarch of Egypt]) asked Joseph's brothers what they did for a living:
Genesis 47:3
“Pharaoh asked the brothers, ‘What is your occupation?’ ‘Your servants are shepherds,’ they replied to Pharaoh, ‘just as our fathers (their actual Hebrew father Israel, and their other Hebrew ancestors: all shepherds) were.’ ”
So therefore, in having these animals, Abraham could have just been influence by his culture as a Hebrew and not necessarily have truly known about the difference between animals (and possibly some Hebrews/if not all of them at this time had somewhat kept the knowledge of clean animals by primarily keeping mainly flocks of clean animals like sheep and goats).
however, this time (unlike the absence of Unclean animals before the flood) it mentions he owned and raised both clean and unclean animals alike: along with cows, sheep and Goats Abraham also kept and raised Camels and Donkeys (unclean animals)!
So, while Abraham did have a lot of clean animals (specifically cows sheep and goats: which could have just been a part of his culture as a Hebrew) he also kept unclean animals as well so the mention of a lot of clean animals does not necessarily prove Abraham knew the difference between clean and unclean animals/meats.
However, this next hint does, much better:
God said Abraham obeyed (thus knew) all his commands (laws):
Genesis 26:5
“...Abraham obeyed me and did everything I required of him, keeping my commands, my decrees, and my instructions.”
Well apart of those commands God had revealed to humans before this time was the knowledge of clean and unclean animals/meats: and though not a direct command, it seems God would only be pleased (like Noah) with Abraham totally if he only sacrificed clean animals to him:
And Abraham is described as doing just that! Wherever God himself commanded him what to sacrifice to him:
Genesis 15:7-10
“ the Lord said to him, ‘Bring me a heifer, a goat and a ram,...along with a dove and a young pigeon.’ Abram brought all these to him,"
Cows, goats, rams, doves, and pigeons are all clean animals worthy to be sacrificed to God almighty!
But Notice also, God did not ever command an unclean animal to be sacrificed to him:
There is no mention of God commanding a pig, a rat, or a vulture to be sacrificed to him: these unclean animals would have most likely been an abomination of an offering to God! Therefore, he would most likely never command Abraham to sacrifice them to him)
Or Abraham made the sacrifice himself to God:
While Abraham's sacrifices to God are not really mentioned as what animal he specifically used in the sacrifices, it seems like he mainly used lambs generally as sacrifices to God as noted in the question his son asked him when about to be sacrificed, but didn't yet realize it:
Genesis 22:7
Isaac spoke up and said...'where is the lamb for the burnt offering?' ”
Isaac his son (who had probably watched his father make many sacrifices to God) did not say where is the piglet? or where is the camel calf? (which they definitely had) he specifically asked his dad where the lamb was: this was most likely because Abraham mainly sacrificed lambs (a clean animal) to God.
Thus Abraham would have to know the correct clean animals to sacrifice to God (and thus the unclean ones to not sacrifice to him) in order to fully obey/please him: therefore, even though Abraham also kept and raised certain unclean animals (Camels and Donkeys) it doesn’t seem he used these animals as sacrifices to God.
along with that, if God also wanted humans to not eat unclean animal's meat at this time as well (as he later commands his future holy people Israel to do) Abraham would have been disobeying him by eating unclean animal meats just like all the other seemingly ignorant Noahites he lived with: but rather it seems Abraham was only eating clean animal meats:
Like the meal he literally fixed for God himself (along with two other men: strongly hinted to be the two angels that went to save Lot and destroy Sodom and Gomorrah) appearing in human form:
Genesis 18:1-8
“ The Lord appeared to Abraham…Abraham looked up and saw three men standing nearby. When he saw them, he hurried from the entrance of his tent to meet them and bowed low to the ground. He said, ‘If I have found favor in your eyes, my lord, do not pass your servant by….. Let me get you something to eat, so you can be refreshed and then go on your way—now that you have come to your servant.’ ‘Very well,’ they answered, ‘do as you say.’So Abraham…ran to the herd and selected a choice, tender calf and gave it to a servant, who hurried to prepare it. He then brought some curds and milk and the calf that had been prepared, and set these before them. While they ate, he stood near them under a tree.”
Though it was not really an offering, this could be considered a type of sacrifice to God, since one of these men was God himself eating this meal! Abraham most likely wouldn’t dare tell his servant to kill a young camel calf and serve it to them nor a young donkey either!
Though this was a special meal, this is most likely the types of meats Abraham often ate (that is, clean animal meats like lamb/mutton [Sheep meat], goat, and beef [cow meat]) thus more proof Abraham knew the difference between clean and unclean animal meats to fully obey all of God's commands for humans at this time.
However, if Abraham did know the difference between clean and unclean animals then why did he keep unclean animals (Camels and Donkeys)?
Did this mean Abraham didn’t know about clean and unclean animals by keeping these unclean animals?
Not necessarily, because he (and his family) are only described as riding these animals ( as Camels and Donkeys were commonly used in the Middle East for at this time) they are never mentioned as being sacrificed to God (as mentioned before, there is no record of Abraham sacrificing Camels, donkeys, or even horses or any other unclean animals of any kind to God: since God most likely would not command nor tolerate an unclean animal sacrificed to him ) nor being eaten by them; they just seemed to be just used for carrying loads and transport (which does not necessarily defy God clean and unclean animals)
This also prove even though an animal is unclean this does not necessarily mean it cannot be used for other purposes beside food and sacrifices (like camels and donkeys; horses are unclean animals, yet they can be used for transport and caring loads, and this seems to be okay to God because he never calls out Abraham [nor any of his descendants] for raising Camels and donkeys for riding).
So ultimately, Abraham most likely did know about clean and unclean animals/meats just like Noah did and if he did, he would certainly would have passed this knowledge along to his son Isaac and his son would had passed this knowledge to his descendants Israelites.
It's very possible that the Israelite before God made the old covenant with them, might have known the difference between clean and unclean animals/meats already and possibly (if they did not forget it in Egypt) just might still have knowed during the making of the old covenant.
But ultimately, the knowledge of unclean and clean animals/meats definitely was known to humans (and most likely they learned this from God at some point) and it seems only clean animals were sacrificed to God and later (under the Noahic covenant) were then eatened by obedient Humans before the old covenant.
Sources:
[1]
(Even though in English the word 'flock' can mean any group of animals from goats, birds, to even humans in the original Hebrew this word only specifically referred to a group of sheep and goats.)
[A]
Hebrew interlinear “Genesis 4:2” by Biblehub
Website:
https://biblehub.com/text/genesis/4-2.htm
[B]
Strong’s Hebrew #6629--“צאֹן”(tsone)--small cattle, sheep and goats, flock, by Biblehub
Website:
https://biblehub.com/hebrew/6629.htm
[2]
(Like flock, the English word 'livestock' can refer to any farm animal raised for meat/products [this list can include pigs and even horses] as well as 'herd' (as this word is sometimes translated) can also refer to groups of any hoofed animals including elephants [which are unclean] but in the original Hebrew it specifically refers to a group of cattle: most likely cows/oxen)
[A]
Hebrew interlinear “Genesis 4:20” By Biblehub
Website:
https://biblehub.com/text/genesis/4-20.htm
[B]
#4735--“מִקְנֶה” (mik-neh')--cattle, by Biblehub
Website: