Actually at least nowadays this doesn't seem to be the case (anymore?). I remember this post in /r/mapporn, which shows that in the UK, US, Canada and Australia, poultry is the most popular kind of meat. (source by /u/visvis)

Of course this doesn't mention any historical data though.

I think you may find the dominant protein to be regional and based on environment/access/resources.

The popularity of eating beef in England seems to date from the Tudor period. Ben Rogers contends that the English developed market institutions and reliable food supplies earlier than their neighbours and also ate more meat than them. The price of beef declined in comparison with other meats during the 16th and 17th centuries, leading to greater consumption. Whereas the price of beef merely doubled in the period 1500-1650, the price of rye increased 8x, wheat 7x, peas 6x and egg/milk 4x.

In 1562 an Italian merchant Alessandro Magno wrote of his stay in London:

It is extraordinary to see the great quantity of meat - beef and mutton - that comes every day from the slaughter-houses in this city, let alone the meat that is sold at a special market held every Wednesday for meat brought in from outside the city. Truly, for those who cannot see it for themselves, it is almost impossible to believe that they could eat so much meat in one city alone. The beef is not expensive, and they roast it whole, in large pieces. They do not care a much for veal as we do.

In his Compendyous Regyment, or a Dyetary of Health (1542), the English physician Andrew Boorde wrote that "Beef is a good meate for an Englyssheman". Thomas Cogan's The Haven of Health, Made for the Comfort of Students (1584) claimed:

Beef is of all flesh the most usual among English men…I need not to show how plentiful it is throughout this land, before all other countries, and how necessary it is both by sea and for the victualing of ships, and by land for good housekeeping, insomuch that no man of honor, or worship, can be said to have good provision for hospitality, unless there be good store of beef in readiness. And how well it doth agree with the nature of Englishmen the common consent of all our nation doth sufficiently prove.

English cookbooks from this era are abundant in recipes including beef. Elizabethan writer Thomas Nashe publicly worried about the reputation Englishmen had for burying their "Spirits in Beef-pots". Shakespeare has the French say in Henry V (1599):

RAMBURES: That island of England breeds very valiant creatures; their mastiffs are of unmatchable courage. ...

Constable: Just, just; and the men do sympathize with the mastiffs in robustious and rough coming on, leaving their wits with their wives: and then give them great meals of beef and iron and steel, they will eat like wolves and fight like devils.

ORLEANS: Ay, but these English are shrewdly out of beef.

Constable: Then shall we find to-morrow they have only stomachs to eat and none to fight. Now is it time to arm: come, shall we about it?

ORLEANS: It is now two o'clock: but, let me see, by ten We shall have each a hundred Englishmen.

The popularity of beef increased during the 17th century, surpassing mutton. There also developed the practice of Scottish and Welsh farmers sending cattle to the English Midlands to be fattened; in the 1680s in excess of 150,000 Scottish cattle were exported to England (178,000 were exported during the seven years after 1696). A similar figure were also exported from Wales. In 1698 the French writer Henri Misson wrote that "it is common Practice, even among People of good Substance, to have a huge Piece of Roast-Beef on Sundays, of which they stuff till they can swallow no more, and eat the rest cold, without any other Victuals, the other six Days of the Week". Around this time, the French began labelling the English "rosbifs".

It was during the 18th century when the association between England and beef came into its own. The Swiss traveller de Muralt wrote in his Letters describing the Character and Customs of the English and French Nations (1726) that "roast beef, which is the favourite dish as well at the king's table as at a tradesman's; 'tis common to see one of these pieces weigh from twenty to thirty pounds...this may be said to be (as it were) the emblem of the prosperity and plenty of the English". Henry Fielding's aforementioned ballad The Roast Beef of Old England also dates from around this time and in 1748 Hogarth famously bashed the poor, beef-deprived French in his painting The Gate of Calais or O, the Roast Beef of Old England.

Sources: Robert Applebaum, Aguecheek's Beef, Belch's Hiccup, and Other Gastronomic Interjections: Literature, Culture, and Food Among the Early Moderns (University of Chicago Press, 2008). Ben Rogers, Beef and Liberty: Roast Beef, John Bull and the English Nation (Vintage, 2004).