<P> During the Miocene, the atmosphere and climate were relatively stable . If anything, CO increased gradually from 14 to 9 million years ago before settling down to concentrations similar to the Holocene . This suggests that it did not have a key role in invoking C evolution . Grasses themselves (the group which would give rise to the most occurrences of C) had probably been around for 60 million years or more, so had had plenty of time to evolve C, which, in any case, is present in a diverse range of groups and thus evolved independently . There is a strong signal of climate change in South Asia; increasing aridity--hence increasing fire frequency and intensity--may have led to an increase in the importance of grasslands . However, this is difficult to reconcile with the North American record . It is possible that the signal is entirely biological, forced by the fire - (and elephant?) - driven acceleration of grass evolution--which, both by increasing weathering and incorporating more carbon into sediments, reduced atmospheric CO levels . Finally, there is evidence that the onset of C from 9 to 7 million years ago is a biased signal, which only holds true for North America, from where most samples originate; emerging evidence suggests that grasslands evolved to a dominant state at least 15Ma earlier in South America . </P> <P> Transcription factors and transcriptional regulatory networks play key roles in plant development and stress responses, as well as their evolution . During plant landing, many novel transcription factor families emerged and are preferentially wired into the networks of multicellular development, reproduction, and organ development, contributing to more complex morphogenesis of land plants . </P> <P> Secondary metabolites are essentially low molecular weight compounds, sometimes having complex structures . They function in processes as diverse as immunity, anti-herbivory, pollinator attraction, communication between plants, maintaining symbiotic associations with soil flora, or enhancing the rate of fertilization, and hence are significant from the evo - devo perspective . The structural and functional diversity of these secondary metabolites across the plant kingdom is vast; it is estimated that hundreds of thousands of enzymes might be involved in this process in the entire of the plant kingdom, with about 15--25% of the genome coding for these enzymes, and every species having its unique arsenal of secondary metabolites . Many of these metabolites are of enormous medical significance to humans . </P> <P> The purpose of producing so many secondary metabolites, with a significant chunk of the metabolome devoted to this activity is unclear . It is hypothesized that most of these chemicals help in generating immunity and, in consequence, the diversity of these metabolites is a result of a constant arms race between plants and their parasites . Some evidence supports this case . A central question involves the reproductive cost to maintaining such a large inventory of genes devoted to producing secondary metabolites . Various models have been suggested that probe into this aspect of the question, but a consensus on the extent of the cost has yet to be established; as it is still difficult to predict whether a plant with more secondary metabolites increases its survival or reproductive success compared to other plants in its vicinity . </P>

Which of the following lists is the right sequence in the evolution of plants