Why could Darwin’s pangenesis not explain heredity according to modern biology?

Darwin’s theory of pangenesis is considered incorrect by modern biology because it relies on a flawed mechanism for the transmission of traits. Darwin proposed that all body organs shed invisible particles called "gemmules" into the bloodstream, which then collected in the germ cells to form the offspring.12

This hypothesis fails for several reasons:

• Biological Inaccuracy: Modern knowledge of embryology shows that germ cells (eggs and spermatozoa) are often developed before an individual reaches adulthood, contradicting the idea that they are formed by particles shed from mature organs.1
• Lack of Evidence: Experimental attempts to locate these hypothetical gemmules, such as those conducted by Sir Francis Galton, failed to find any evidence of their existence.2
• Mendelian Genetics: We now know that heredity is governed by genes and alleles located on chromosomes, rather than particles derived from peripheral body parts.2
• Germ Plasm Continuity: As noted by August Weismann, the continuity of the germ plasm is sufficient to explain the inheritance of characteristics without requiring contributions from somatic body cells.1