Cranial capacity refers to the volume or size of the brain case, which can give us an indication of the brain size and potentially brain functionality of different species. In this case, we are comparing the cranial capacities of several early human ancestors: Cro-Magnon Man, Neanderthal Man, Java Man, and Peking Man.

1. Cro-Magnon Man:
- Cro-Magnon Man refers to the early modern humans who lived in Europe between 40,000 and 10,000 years ago.
- They are considered anatomically modern humans and are the closest ancestors to contemporary humans.
- The average cranial capacity of Cro-Magnon Man is estimated to be around 1,600-1,700 cubic centimeters (cc), which is similar to the average cranial capacity of modern humans.

2. Neanderthal Man:
- Neanderthals lived in Europe and Asia between 400,000 and 40,000 years ago.
- They had a robust build, with a stocky body and distinctive facial features.
- The average cranial capacity of Neanderthal Man is estimated to be around 1,400-1,700 cc, which is larger than that of modern humans on average.

3. Java Man:
- Java Man, also known as Homo erectus, is an extinct hominin species that lived in Java, Indonesia, between 1.8 million and 300,000 years ago.
- They had a more primitive anatomy compared to modern humans and Neanderthals.
- The average cranial capacity of Java Man is estimated to be around 900-1,100 cc, which is smaller than that of modern humans and Neanderthals.

4. Peking Man:
- Peking Man, also known as Homo erectus pekinensis, is an extinct subspecies of Homo erectus that lived in China between 700,000 and 200,000 years ago.
- They are known for their use of fire and the presence of stone tools at their archaeological sites.
- The average cranial capacity of Peking Man is estimated to be around 900-1,225 cc, which is smaller than that of modern humans and Neanderthals but larger than that of Java Man.

Based on the information provided, the correct answer is option 'A', Cro-Magnon Man, as they had the highest cranial capacity among the given options. However, it is important to note that cranial capacity is just one aspect of brain anatomy and does not necessarily reflect intelligence or cognitive abilities.