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The grass family includes more than 10,000 species. It includes common lawn grass to food grains- such as rice, wheat, maize, to lilies, orchids, pineapples, palms, bamboos. It forms an important part of the urban, suburban landscape, as well as, wild landscape in much of the world. Members of the family also are ecological dominants, covering more than 30% of the earth’s land surface. Grasses, unlike most other plants, have evolved to grow not from their tips but from closer to their roots. This growth from the roots attribute allows them to survive fires, freezing temperatures, drought, and even flooding.


The evidence of grass is dated back to 70 mya (fossilized pollen found in Maastrichtian deposits of Africa and South America), but the firm records of grass pollen are from 60-55 mya. This date is after the major K-T extinction (K-Pg) event that wiped the dinosaurs, and destroyed the plant landscape, as well (75% or more of all species on Earth disappeared). Out of the ashes, thrive the new plant form- grass (mammals as well).

for details see- “The Major Extinctions on the Earth”

The grass evolved at the time of the Paleocene–Eocene Thermal Maximum (PETM), a period with more than 8°C warmer global average temperature than today. Unlike other plants (C3 photosynthesis), grasses adopted a new photosynthesis process, called C4 photosynthesis. It is advantageous under low atmospheric CO2 and/or high temperatures, where photorespiration rates are relatively high in C3 plants. Under warm conditions, the efficiency of C4 photosynthesis is greater than that of C3 photosynthesis.

In a study, the researchers examined a series of sediment cores drilled by a research ship in the Red Sea and the western Indian Ocean, off northeast Africa. The cores contain chemicals created by vegetation on land that were later washed or blown out to sea, and laid down in layers for tens of millions of years. Using a fairly-new technique, researchers analyzed carbon-based chemicals called alkanes, which make up the waxy outer parts of leaves, and contain the fingerprints of different ancient plant life in much of what is now Ethiopia and Kenya, the assumed birthplace of hominid.

The result strongly suggests, sediments between 24-10 mya (long before any direct human ancestors appeared) has alkanes signature, a form of photosynthesis used mainly by woody plants, the so-called C3 pathway. There were few grasses, and woodlands thus presumably dominated. Then, with an apparent shift in climate, starting from 10 mya, a different form, linked mainly to grasses, the C4 pathway began to showing up. The area covered by grass seemed to grow 7-8% every million years. The study shows that the trend continued through all known human evolution, leading to a dominance of grasses. This kind of vegetation is still the main plant life in east Africa today. Other scientists have shown that grasslands spread also in south Asia, the Americas, and southern Africa somewhat later.

In response to thinned out of dense forests, which produced ‘mosaics’ of forests, woodlands and grasslands, it seems likely that some hominid maintained a forest-oriented adaptation, while others may have begun to exploit forest margins, and grassy woodlands. Early hominid began walking upright largely in response to this environmental change, in particular, to the growing incidence of open spaces, and the way that changed the distribution of food. The process of increasing commitment to bipedalism probably involved an extended and complex opening of habitats, rather than a single, abrupt transition from dense forest to open savanna.
This adaptation of upright walking eventually lead to tool making, by using the free hand, and was associated with drier habitat and the spread of grasslands, an idea often known as the savanna hypothesis. According to this, many important human adaptations arose in the African savanna, and influenced by the environmental pressure of expanding dry grassland.