The paper by De Lucia and Blaizot investigates the formation and evolution of brightest cluster galaxies (BCGs) using semi-analytic techniques. They find that BCGs form extremely hierarchically, with a significant portion of their stars forming in small galaxies at high redshifts ($z \sim 5$) through rapid cooling rather than merger-triggered starbursts. The final mass of BCGs is assembled surprisingly late, with half of it typically concentrated in a single galaxy by $z \sim 0.5$. Most of the galaxies that accrete onto BCGs have low gas content and red colors, suggesting that late mergers do not significantly alter the apparent age of BCGs. The accumulation of a large number of old stellar populations, driven by the merging history of the dark matter halo, explains the observed homogeneity in BCG properties. The authors also discuss the evolution of BCGs to high redshifts, comparing their model predictions with observational data. They find qualitative agreement between their model and high-$z$ observations, suggesting that high-$z$ BCGs belong to the same population as the massive end of local BCG progenitors. However, high-$z$ BCGs are not necessarily the same galaxies as those in the local Universe, and only a fraction of them become massive galaxies in the local Universe. The study provides insights into the hierarchical formation and evolution of BCGs, highlighting the complex interplay between galaxy mergers, star formation, and feedback processes.The paper by De Lucia and Blaizot investigates the formation and evolution of brightest cluster galaxies (BCGs) using semi-analytic techniques. They find that BCGs form extremely hierarchically, with a significant portion of their stars forming in small galaxies at high redshifts ($z \sim 5$) through rapid cooling rather than merger-triggered starbursts. The final mass of BCGs is assembled surprisingly late, with half of it typically concentrated in a single galaxy by $z \sim 0.5$. Most of the galaxies that accrete onto BCGs have low gas content and red colors, suggesting that late mergers do not significantly alter the apparent age of BCGs. The accumulation of a large number of old stellar populations, driven by the merging history of the dark matter halo, explains the observed homogeneity in BCG properties. The authors also discuss the evolution of BCGs to high redshifts, comparing their model predictions with observational data. They find qualitative agreement between their model and high-$z$ observations, suggesting that high-$z$ BCGs belong to the same population as the massive end of local BCG progenitors. However, high-$z$ BCGs are not necessarily the same galaxies as those in the local Universe, and only a fraction of them become massive galaxies in the local Universe. The study provides insights into the hierarchical formation and evolution of BCGs, highlighting the complex interplay between galaxy mergers, star formation, and feedback processes.