The issue focused on debate between physics and biology about whether evolution results from natural selection or selection through genetic drift and mutation in populations with moderate diversity (small populations). Both approaches account for variation within populations by adjusting population sizes for biological variation and measuring gene expression levels at multiple sites within populations. Both approaches involve adjusting genetic drift rates at multiple sites within populations and measuring gene expression levels at multiple sites within populations. Both approaches involve analyzing genes from populations at multiple sites within populations and observing gene expression differences within populations and observations within populations