Concept · Ch 5
The same answer, five times
Convergent evolution is what happens when unrelated floras are handed the same hard climate — hot dry summers, wet winters, recurring fire — and independently arrive at the same design: low, hard-leaved, fire-tuned shrubland.
First, meet: The Mediterranean bargain (two seasons, not four)
Somewhere on five separate coastlines, on five separate continents, plants that have never met and share no recent common ancestor sat the same exam and turned in the same answer.
Give any flora on Earth the same brief — a killing-dry summer, a mild wet winter, and fire that will, sooner or later, come through — and it converges on the same design: low, hard-leaved, evergreen shrubland (Cowling et al. 1996).
Biologists call this trick convergent evolution, and it usually gets illustrated with a shark and a dolphin, two unrelated animals arriving at the same torpedo shape because the ocean set the same problem for both.
Here it is written across whole landscapes.
The maquis and garrigue of the Mediterranean basin, the chaparral of California, the matorral of central Chile, the fynbos of the Cape, and the kwongan and mallee heaths behind Adelaide belong to different plant families entirely, and each region’s flora assembled its version of the kit on its own timetable, continents and epochs apart, as a Mediterranean climate arrived there in its own turn (Rundel et al. 2016).
What they share is not ancestry but homework: small, stiff, water-hoarding leaves — the trait called sclerophylly, “hard leaf” — and a matching set of fire habits, resprouting from buds tucked safely under the bark, sealing seed inside woody fruit that only a fire will crack open, and holding germination back until the seed tastes smoke or heat (Keeley et al. 2012).
Walk the low grey-green heath on the range front above Adelaide and you are standing in the same room as a Cape fynbos slope or a California chaparral hillside — different cast, same script, same climate having auditioned each separately and liked the same answer.
The pay-off for the planet is wildly out of proportion to the real estate involved.
Between them the five Mediterranean regions cover well under two per cent of Earth’s land, yet they carry something like a sixth of all its vascular plant species (Cowling et al. 1996) — hardship, given enough time, breeds invention rather than merely paring a landscape back.
Everything the rest of this gulf-to-range gradient shows you — the sandy heaths, the mallee, the stringybark forest on the ranges — is a local entry in that same five-way convergence, and none of it is an accident of Adelaide alone.
Go deeper — the mechanism & the evidence
Convergence here is not one trait but a whole survival kit, assembled independently on five continents from unrelated ancestry. The clearest shared response is sclerophylly — small, stiff, evergreen, water-hoarding leaves — but the deeper convergence is in fire behaviour: resprouting from buds shielded under bark, seed locked into woody fruit that only fire cracks open (serotiny), and germination withheld until a seed tastes smoke or heat (Cowling et al. 1996; Keeley et al. 2012). None of these five floras inherited the trick from a common ancestor — the Cape's fynbos, the Mediterranean's maquis and Australia's kwongan/mallee heaths sit in entirely different plant families and diverged tens of millions of years before any of them met a Mediterranean climate. What they share is the selection pressure, not the pedigree, and Rundel et al. (2016) trace how each region's flora assembled its version of the kit on its own timetable as the climate itself arrived, region by region, over the Neogene. The payoff is disproportionate: together these five regions hold something like a sixth of the world's vascular plant species on well under two per cent of its land (Cowling et al. 1996) — hardship, given geological time, breeding invention rather than merely paring life back.
Sources & further reading
Every claim here is traceable. Each citation links to its entry in the bibliography.
- Cowling, R.M., Rundel, P.W., Lamont, B.B., Arroyo, M.K. & Arianoutsou, M. (1996). Plant diversity in mediterranean-climate regions. Trends in Ecology & Evolution 11(9):362-366. https://doi.org/10.1016/0169-5347(96)10044-6 — Convergent sclerophyll shrubland and the disproportionate plant diversity of the five Mediterranean-climate regions.
- Rundel, P.W., Arroyo, M.T.K., Cowling, R.M., Keeley, J.E., Lamont, B.B. & Vargas, P. (2016). Mediterranean Biomes: Evolution of Their Vegetation, Floras, and Climate. Annual Review of Ecology, Evolution, and Systematics 47:383-407. https://doi.org/10.1146/annurev-ecolsys-121415-032330 — Independent evolutionary assembly of each region's Mediterranean flora and vegetation.
- Keeley, J.E., Bond, W.J., Bradstock, R.A., Pausas, J.G. & Rundel, P.W. (2012). Fire in Mediterranean Ecosystems: Ecology, Evolution and Management. Cambridge University Press. — Shared fire-survival traits — resprouting, serotiny, smoke/heat-cued germination — across the five regions.
See it in the country
Grounded in A Coast Running Out of Water. Every figure is stated once in the book's canonical facts register and cited to a published source.