‘Without plants, there can be no other stories on Earth — marvels of evolution, plants permit life’

William E. Friedman

is director of

Harvard University

’s

Arnold Arboretum

and teaches evolutionary biology. Speaking to Srijana Mitra Das at Times Evoke, he shares the story of how plants evolved — and enabled human life:


What is the core of your research?

I’m an evolutionary biologist. I think of myself as an evolutionary historian — my work seeks to understand the birth and early diversification of flowering plants, the predominant source of diversity among photosynthetic land plants. But they are also a relatively recent group which evolved about 140 million years ago whereas conifers or cycads go considerably farther in time.




My work is also embryological where I study the fertilisation process and how in particular mothers nourish their progeny within seeds. One of the great mysteries of flowering plants is how they nourish their progeny with a tissue called endosperm — two out of every three calories of food humans consume is endosperm, manifest in a grain of rice, maize, etc. Without endosperm in plants, humans wouldn’t be here.

What is the extent of plant life on Earth — and what determined its evolution?

There are estimates of 3,50,000 to 4,00,000 different species of land plants. As many remain undescribed, even this number could be higher. Plants show us how with evolution, nothing remains static — consider the fact that two billion years ago, there was only a single cell photosynthetic organism swimming in the waters of the world. Descended from that organism, the common ancestor, are all the flowers and ferns on Earth.

TOUGH BUDS: The

Hamamelis

vernalis, part of the witch-hazel family, bursts into bloom in late winter when very little life can grow. Picture courtesy: W. Friedman, Arnold Arboretum

About 475 million years ago, there were no land plants on Earth — just then, the first little green algae start to encroach on the edges of wet areas. They begin evolving greater tolerance to drier conditions. From there, it took millions of years before land plants that were a few centimetres tall emerged. Trees only came about 380 million years ago. There was a time on Earth when plants would only come up to our waist. It took entire eras when plants figured out how to grow tall, increase their girth to support their weight and so on. All the flowers we know today only start to evolve about 135 million years ago.



So, this evolutionary story goes back millions of years when plants figured out the trick of turning the energy of light into chemical bonds. Without plants, there can be no other stories on Earth — until plants put energy into life systems, heterotrophs like us have nothing to eat. Plants shaped the biosphere through carbon dioxide levels, geochemistry, rain, etc. The history of Earth is thus a dialogue between non-living and living elements, where each changes and moulds the other.

WE LIVE AMONG GIANTS: Flowering plants like the Euonymus sachalinensis began to evolve 135 million years ago while human beings started only seven million years ago. Picture courtesy: W. Friedman, Arnold ArboretumWhat is sociobiology?
This is the idea that organisms interact and these interactions evolve based on relationships. People often assume that behaviour requires neurons — but behaviour is not about thinking. It is comparable to being genetically programmed.

In plants, evolved behaviour is about how you relate to relatives that can help your genes survive. Mother plants, for instance, unlike fathers, also provide the food seeds need to grow. But this is not a random process — mothers can test the quality of their progeny. They can even test the compatibility of potential fathers. So, there is a great deal of knowledge about relationships in the plant world. But these are not thinking behaviours — these are wired-in due to the ability to detect relationships.

How do you envision the future of the plant world in an era of climate change?
The plant world faces many climate impacts and I’m not too optimistic, given the human capacity to produce damage. Earth is facing climate change — but it is also facing other human impacts like burning rainforests or cutting trees to put livestock in their place. Every hamburger we eat, we are contributing to extinction.

We have only two options before us. We could either discover the impacts of our current behaviour so late that while humans will go extinct, a great deal of non-human life won’t — the world will keep spinning with life but without us. Or, we could figure out how to live in greater harmony with the millions of species on Earth which have evolved over a four-billion-year journey, from the first cell of life to this moment. We live amidst this utterly magnificent and unique sequence of events — are we humans going to blow it up?

We have already done great damage because we just don’t see beyond ourselves. Think about the phenomena of plant blindness — we walk by plants every day and we don’t even notice them. We don’t give them standing. We don’t care to look but here are these wondrous species that are simply magnificent — and truly evolved.

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