It's always been a central thesis of memetics that this is only one way of looking at the situation. As well as focusing on the cultural hosts, one can alternatively model the cultural symbionts themselves. The cultural symbionts have their own life cycles and lineages - which are independent of those of their hosts. From this perspective the hosts are one part of the environment. The environment includes multiple other copying devices (such as printing presses) and multiple other sources of selection (such as fires). Animal brains are just one part of this bigger and better picture.
It is worth noting that biology has gone through this conceptual revolution once before. It was once not widely recognized that many diseases were caused by microscopic pathogens - such as bacteria and viruses. The germ theory of disease was developed in the 19th century. Before that time, many diseases were modeled in a variety of ways using many inaccurate theories. Miasma theory held that some contagious diseases were the result of airborne pollutants. Sometimes pathologies were considered to be the results of hauntings, curses, karma, witchcraft or the work of the gods. Some of the theories came close to the right answer. The ideas of demonology and possession attributed some maladies to the actions of external agents that lived inside the host's body. These theories were partly validated by the germ theory of disease - though the causitive agents turned out to be rather different.
I think we are now facing a situation which is similar to that faced by 19th century physicians - with the modern study of culture. The cultural equivalent of the germ theory of disease is the the germ theory of culture. This was proposed by Cloak (1975) and Dawkins (1976). As with the germ theory of disease, the idea faced resistance, and took a considerable quantity of time to be widely adopted - 50 years approximately. Memetics further supports the basic model present in demonology and possession - that pathology is caused by invasion of hostile agents from outside the body - which can potentially be evicted again.
Today people routinely talk about culture "going viral". Cultural epidemiology has been enshrined in the dictionary - in the form of "memes" and "contagions" - which dictionaries explicitly acknowledge take cultural forms. However, the whole the idea still faces resistance within academia. Many still just don't understand that "viruses of the mind" are real things that can cause or contribute to pathologies. The concept is widely denigrated as being an imperfect "analogy". Others describe fear of manipulation by microscopic entities as "Darwinian Paranoia". Others opine that cultures are complex wholes that can't be meaningfully split up into germ-like pieces - and so on.
It is rather tragic to watch this situation unfolding - in the light of all those who died during the development of the germ theory of disease. You might think we had learned that small, information-carrying entities that can be transmitted between hosts can cause real problems. A wider recognition of the germ theory of culture seems likely to lead to more and better diagnosis and treatments of transmissible pathologies - just as happened with the the germ theory of disease.