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Repeated evolution: Placental structure evolved several times, then has been lost, and then re-evolved many times

i know that stuff happens but anyway… all this by random mutations ?

In Poeciliopsis fish, eggs are retained within the follicle after fertilization and throughout embryonic development (Wourms and Lombardi 1992). Most species are lecithotrophic, relying on yolk, but in others, a highly folded, follicular epithelium forms a “follicular placenta” with the embryonic pericardial sac. This epithelial layer is lined with microvilli, while the surrounding tissue is highly vascularized, presumably to facilitate maternal-fetal exchange (Kwan, et al. 2015).

This type of placental structure has arisen several times during Poeciliopsis evolution (Kwan, et al. 2015) and has been subsequently lost and regained many times, making it a model for the evolution of placentation (Pollux, et al. 2014).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5033709/

and similar stuff happened here:

Have Wings Come, Gone and Come Again?

Can complex traits be re-evolved by lineages that have lost them? Phylogenetic study now suggests that wings may indeed have reappeared several times within the ancestrally wingless stick insects.

https://www.sciencedirect.com/science/article/pii/S0960982203003646