In 1:26 “man” is without the definate article and there is the plural pronoun so it is used to refer to the race, but in 1:27a it has the definate article and is singular, not collective therefore it speaks only of the first human being that God created. In 1:27b he made them male and female. (This is the same thing that we are told in Genesis 2 when the woman is created, the difference being it is said put in different words) In 1:27b and 1:28 the plural pronoun “them” is being used again because “adam” is again being used to refer to the race, but in 1:27a, it has the defintae article as it is only refering to Adam, the first human being. This is also in line with Gen 2. We know that first there was only one human that was created and then there was two.
There was something about this argument that didn’t seem right to me. Why would the author address the creation of the adam = humanity in v. 26 only to shift it to adam = the first man in v. 27a then back to a discussion about male and female in v. 27b which would be connected to v. 26. It seemed to me that there is a better explanation for why adam in v. 26 is indefinite and adam in v. 27a is definite.
Now I can use help from my more grammatically apt friends out there but I suggest that this is an anaphoric usage of the article. In other words the reason for making adam in v. 27a definite is because it refers back to the same “adam” in v. 26. It is like saying, “The adam that I just mentioned was made in God’s own image”. This seems to me to make better sense than the suggestion that we have humanity as the subject of v. 26, Adam in v. 27a, and humanity against (as male and female) in v. 27b.