In his experiments with garden peas, Mendel found that one physical unit is inherited from the father and one from the mother. For what did this provide evidence?

It provides evidence for the law of segregation of Genes.

Explanation:

Genetically, the genetic composition of each new individual eukaryotes is obtained from combination of alleles (haploid sex cells) of the parents' genes. Therefore the diploid cells formed from the combination of alleles in the offspring was as a result of segregation or separation of the parents' alleles from the (diploid to haploid) on the same gene locus independently of one another at meiosis (during spermatogenesis and oogensis).

The results is combination of entirely new alleles (diploid cells) in new offspring. This forms the basis of Law of segregation of genes which states that Alleles of a gene on the same locus segregate / separate independently of one another.

It forms the basis of variation