A gasoline engine "comes to life" only when many different independent conditions are met at the same time. Take away the spark plug, and it will not run at all. Leave out the pistons, and it will not run. Without oil or gasoline, it will not run. The list of interdependent conditions goes on and on. Even if all other conditions are met, it must be given an initial crank in order to start. Likewise, living creatures have inter-dependent characteristics which determine their very existence. Photosynthesis does not work without the conversion of energy into enzymatic and dark reaction cicle activity.
Compared to photosynthesis, a gasoline engine is extremely primitive. In order for photosynthesis to arise spontaneously, the sum of the parts of enzymes, genes, proteins , and protein complexes would have to come together intact in order to function, and the chemical reactions which would produce glucose would have to be started all at once.
What type of biological system could not be formed by “numerous successive, slight modifications?” Well, for starters, a system that is irreducibly complex.
By irreducibly complex I mean a single system composed of several well-matched interacting parts that contribute to the basic function, wherein the removal of any one of the [core] parts causes the system to effectively cease functioning.
But today, there are many such cases observed in nature.
High information content machine-like irreducibly complex and interdependent structures, of which photosynthesis, the eye, the human body, nitrogenase, the ribosome, the cell, rubisco, photosystem II, the oxygen evolving complex etc. are prime examples, are commonly found in nature.
Since Evolution is unable to provide a advantage of adaptation in each evolutionary step, 1) Darwinism’s prediction is falsified; 2) Design’s prediction is confirmed.