(If you want to double your effectiveness as a Catholic apologist in 30 minutes, read this article.)
Anthropology refers to the study of human nature in general, but within the context of theology it refers to man's nature as it corresponds to his final goal, his abilities, and the effects of Adam's sin. This subject is indispensable in forming good theology, especially when discussing salvation, because if you get this subject wrong, you'll likely get salvation wrong as well. As an analogy, if a medical doctor fails to understand how the body functions, he will most likely fail to properly diagnose and treat the ailment. Well-informed Catholic theologians have understood this and explained why incorrect anthropology is at the heart of the Protestant Reformation. Luther's decision to reject the One Holy Catholic and Apostolic Church came ultimately as a result of him severely erring on his view of human nature, and thus turning that into an erroneous view of salvation. From an apologetics point of view, any discussion with a Protestant is bound to fail if you don't understand that each side has issued a radically different "diagnosis" to the "illness" mankind finds himself in after Adam's disobedience.
The following is a list I compiled with the help of various resources of 7 reasons the Protestant understanding of human nature is severely flawed and even heretical. That might sound harsh, but this specific Protestant error is so severe that even the Incarnation itself is at stake.
1) Jesus was unable to suffer and die. If Jesus was without sin, why was He able to suffer and die if Adam was originally not able to? As with the other reasons, this has to do with the Nature/Grace Distinction: humanity was originally endowed with special gifts of grace, one of them being the gift of immortality. Immortality is that gift which preserves the body from decaying and eventually separating from the soul (i.e. physical death). As a creature, man cannot naturally (that is by his own human powers) stop himself from being subject to the laws of nature, particularly decomposition, and only such a divine gift could halt that process. When he sinned, Adam lost this grace (along with the others) and immediately started the bodily decay process which ended in physical death. Jesus, even being without sin, chose to forego this gift in order to experience pain and suffering as we do. Because Protestants reject the Nature/Grace Distinction, they're forced to say immortality was an essential part of sinless human nature, and thus Jesus would not have been able to die.
2) Faith is Reason. Our created natures are finite, they're limited in their ability to comprehend what is beyond the natural world. Faith is that gift which is able to see beyond creation, to embrace many of the mysteries of God, including the Blessed Trinity. There is no way we could conceive of or deduce various Christians doctrines, especially the Trinity, by philosophy or any such rationalization. We require something extra to 'see' beyond that, and that's the gift of faith (Hebrews 11:1-3). St Augustine gave the analogy of someone with perfect vision still being unable to see in the dark since his eyes are naturally limited in their abilities, but if you add something like a torch, suddenly the eye is enabled to see in the dark. But because Protestants reject the Nature/Grace Distinction, they must claim this ability to believe in the Trinity is natural to man, which is abominable and reduces faith to merely rational arguments. And if they claim this belongs to sinless nature, then they must claim Jesus required faith, which is likewise abominable.
3) Adam could bench-press more than Christ. Protestants teach that Adam was given the task in the garden to keep all the commandments perfectly by his own human powers - i.e. without God's assisting grace. Since Adam failed this task, a substitute was needed, and so Protestants teach Jesus had to keep all those in our place, since we're tainted with sin as well. But unlike Adam, Jesus was "full of grace and truth" from the moment of conception (John 1:14), and Jesus had the Holy Spirit come upon Him at Baptism to begin his mission order to "fulfill all righteousness" (Mat 3:13-15). How is this a fair substitution? What Adam had to do by human effort alone, Jesus was called to do with a humanity endowed with "grace and truth" and the Holy Spirit. But because Protestants reject the Nature/Grace Distinction, this makes Adam's challenge more 'manly' than Our Lord, which cannot be. The only acceptable solution is to conclude Adam's humanity was originally endowed with divine gifts so that he had grace and the Holy Spirit as well, and thus had to originally cooperate with grace in Eden.
4) Christ "was made sin" - literally - at the Incarnation. If Mary had a fallen "sin nature" as Protestants teach, then what exactly could Jesus have been conceived in if not sin? To suggest Mary's human nature was not passed onto Christ, from the fertilized egg to the nourishing of the fetus to the birth, means the Incarnation didn't happen. But if Mary's humanity was passed onto Jesus, then all She could give Him was Her "sin nature," which is obviously unacceptable. Because Protestants reject the Nature/Grace Distinction, they're forced to create two human species, one perfect and the other radically corrupted by the fall (i.e. a "sin nature"), and thus conclude Jesus was of a different human species than His Mother, rendering the Incarnation a fiction. With the Nature/Grace distinction, the very notion of "sin nature" becomes impossible, as human nature doesn't change, it merely loses graces, and thus Mary could pass on Her own humanity to Jesus without any way compromising Christ's holiness. (NB: The situation described above was simply to illustrate a real problem. Mary did not in fact suffer the loss of grace, since as a unique intervention in Salvation history, God preserved Her from any stain of sin from the Moment of Conception.)
5) Luther was roomies with Pelagius... Pelagianism was the heresy that taught man could save himself apart from grace. Though most people think of it as an error that applies only after Adam's sin, the truth is that it applies especially prior to the fall. Pelagius taught this because he saw Adam as originally self-sufficient and thus not needing any divine assistance. This ties in directly with #3 above. Since Adam had no divine gifts to lose, then Pelagius (logically) concluded that nothing damaging befell humanity because there was nothing for Adam to technically 'fall from' (and the alternative option results in the problem described in #4). Because Protestants reject the Nature/Grace Distinction, they've unwittingly embraced Pelagianism. As described in #3 above, Protestants would even require Jesus to be Pelagian, having to keep the commandments by purely human abilities.
6) ...and with Mani. Luther was well aware that Adam's sin caused some very real damage to humanity that made Pelagius' conclusion in #5 above unacceptable. But by accepting Pelagius' starting premise, Luther could only conclude that human nature itself became radically corrupted, even sinful. It is from this Protestants frequently speak of man having a "sin nature". It was no accident that when Saint Augustine opposed the Pelagians, he found himself likewise opposing an earlier heresy known as Manichaeanism. In brief, the Manicheans taught that there was a Dualism in the universe, with opposing good and evil forces. The evil forces were principally material things, and thus sin had a literal existence as "stuff", and this only made sense to them because God was wholly good and thus couldn't create evil. Saint Augustine was caught up in this for a time, until some solid Christians transformed his thinking, and the "Aha!" moment is recorded beautifully in his Confessions (Book 7):
For corruption harms, but, unless it could diminish goodness, it could not harm. Either, then, corruption harms not, which cannot be; or, what is most certain, all which is corrupted is deprived of good. But if they be deprived of all good, they will cease to be. For if they be, and cannot be at all corrupted, they will become better, because they shall remain incorruptibly. And what more monstrous than to assert that those things which have lost all their goodness are made better? Therefore, if they shall be deprived of all good, they shall no longer be. So long, therefore, as they are, they are good; therefore whatsoever is, is good. That evil, then, which I sought whence it was, is not any substance; for were it a substance, it would be good. For either it would be an incorruptible substance, and so a chief good, or a corruptible substance, which unless it were good it could not be corrupted. I perceived, therefore, and it was made clear to me, that Thou made all things good, nor is there any substance at all that was not made by God
Just let that sink in. Saint Augustine realized evil is a "diminishing" of something good, not a 'thing' like a black blob. Just as cold is absence of heat and darkness is absence of light, evil is some deprivation of good. But unlike Pelagius in #5 who (rightly) saw nothing for Adam to "fall from," Luther took this conclusion in the opposite direction and said human nature became inherently sinful, which is a resurrection of a Manichean error. Because Protestants reject the Nature/Grace Distinction, in favor of Luther's view, they've unwittingly embraced Manicheanism along with Pelagianism.
7) Long-distance intimacy with God. In the New Testament, we see what true intimacy with God entails: the indwelling of the Holy Spirit (John 7:38-39), which includes the Father and the Son (John 14:23). This intimacy is strikingly absent from the Protestant view of Adam, and indeed would contradict it, particularly since Adam would have been walking by the Spirit (cf Galatians 6:7-9). Yet there is no other way Adam could have been created in intimacy with God. Because Protestants reject the Nature/Grace Distinction, the original intimacy that Adam shared with God had to have been a purely external relationship, not significantly different from that of unbelievers today have, with no opportunity to ever receive the Holy Spirit.
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For further reading, I strongly recommend listening to the 1 hour lecture by Dr Feingold linked over at the Called To Communion article "Original Justice and Original Sin". You will be a much stronger apologist if you do. This subject needs to be discussed because I find it to be virtually non-existent in most Catholic apologetics resources, yet this was standard Catholic teaching when Thomism was standard in the seminaries.