Why evolution needs development, and medicine needs evolution

For much of the past century, adaptive evolution has been defined as the differential replication of genes that influence the survival or reproduction of their host. Although Darwin is perhaps best remembered today for having co-discovered this principle of natural selection, its evolutionary importance was not widely accepted until several decades after his death. This is in part because Darwin lacked an understanding of the material basis of heredity. His speculations about the mechanism of inheritance, reflected in his Lamarckian model of pangenesis, had fatal flaws. Notably, Darwin envisioned maternal and paternal hereditary contributions to offspring as blending together at conception; his critics noted that this would inevitably lead to the dilution of any novelties, and thus could not explain the gradual rise of complex adaptations via the accumulation of small changes as Darwin's model required. This left a major problem unsolved.