Primitive photosynthetic organisms, morphologically similar to the cyanobacterium Spirulina, have been found as 3.8 billion years old microfossils. Global irradiation without an ozone layer was intense. As a protection, photosynthetics created oligomerization of the evolutionary oldest PSI-type reaction center complex stimulating dissipation of excitation energy. The PSI complex appears in cyanobacteria preferentially as a trimer, whereas in plants it exists as a monomer. P700 and P700⁺ of PSI monomers are about equal quenchers of energy, but P700⁺ in PSI trimers of Spirulina is a much stronger quencher than P700 reduced. The antennae of PSI trimers of Spirulina contain an extremely longwave Chl735 (located peripherally on PsaA/PsaB) that contributes in quenching. The distance between P700 and Chl735 is about 42Å. P700⁺ strongly quenches the fluorescence of Chl735 due to a high overlap of the Chl735 fluorescence and the P700⁺ absorption bands. The rate constant of energy migration to P700⁺ is~ 150 times larger than the one to P700. Therefore the de-excitation is stimulated by an energy flow within the trimeric complex towards a monomer with a P700⁺ where heat is produced. Higher plants also dissipate excess energy via aggregates of LHCII. In vitro the nonradiative decay of LHCII aggregates is at least 40 times faster than that of trimers. Excess light also seems to cause conformational changes stimulating thermal dissipation. Thus, pigment-protein complexes contribute not only in harvesting of light for utilization in photochemistry, but as oligomers they stimulate the dissipation of excess energy, protecting the organism against photodestruction.