TMM IIRC has an a priori argument that we should expect horizontal transmission to beat vertical transmission often: It happens faster. Replication rate of memes is orders of magnitude faster than replication rate of genes. It is surprisingly analogous to viruses/parasites in that regard. Genes do evolve over time to be more resistant to viruses/parasites; this is why the native Americans were disproportionately wiped out by disease compared to Europeans, who were disproportionately wiped out compared to Africans. However, despite this, viruses/parasites remain prevalent in the world, even (especially) in Africa. The solution to the puzzle is that the diseases are evolving too.
TMM IIRC has an a priori argument that we should expect horizontal transmission to beat vertical transmission often: It happens faster. Replication rate of memes is orders of magnitude faster than replication rate of genes. It is surprisingly analogous to viruses/parasites in that regard. Genes do evolve over time to be more resistant to viruses/parasites; this is why the native Americans were disproportionately wiped out by disease compared to Europeans, who were disproportionately wiped out compared to Africans. However, despite this, viruses/parasites remain prevalent in the world, even (especially) in Africa. The solution to the puzzle is that the diseases are evolving too.