land plants

by

Children’s Books About Evolution

Evolution is a difficult subject to learn, let alone teach. Because evolution is generally such a slow process, it involves a timeline that is challenging for us to comprehend. Evolution is also commonly misunderstood, so misconceptions abound, be they purposeful misrepresentations, gaps in understanding, or otherwise. Wrapping one’s brain around even the basic tenets of evolution can take years of study, yet it is one of the most fundamental concepts of biology; failing to understand it stifles one’s knowledge of and appreciation for the study of life on Earth. On the flipside, gaining an understanding of the workings of evolution can inspire a greater appreciation for our place in the universe and can instill in oneself the urgency of conservation.

Despite being a tough subject to grasp, there is no reason why children should be exempt from learning about it. However, because it is such a complex topic, adults can struggle to find ways to explain it. Luckily, there are some great children’s books about evolution that introduce the subject in basic ways. These books are good starting points and can help cultivate a desire to explore the topic further. Understanding evolution and the science surrounding our world and the broader universe is a lifelong pursuit. Children will benefit from a head start.

What follows are reviews of a handful of books that may be useful in teaching kids about the theory of evolution.

I Used to Be a Fish by Tom Sullivan

i-used-to-be-a-fish

This book is an excellent place to start. It is a quick and easy read, and it introduces – in a very simple way – the evolutionary lineage of humans. It doubles as a lesson on evolution and, as Sullivan puts it, “a tribute to every child’s power to transform their lives and to dream big,” which is achieved by highlighting the imagination of the main character and defining evolution as the gradual development over a lifetime towards achieving goals and aspirations.

In the Author’s Note, Sullivan briefly explains some important aspects of evolution: it is “a very slow process” that “occurs over generations to entire populations of creatures,” it doesn’t occur in a straight line like the book implies but instead looks “more like a tree with many complicated branches,” and “it doesn’t happen because a creature wants it to.”

One step in our evolutionary lineage as depicted in I Used to Be a Fish by Tom Sullivan

One step in our evolutionary lineage as depicted in I Used to Be a Fish by Tom Sullivan

Life history

Timeline from I Used to Be a Fish by Tom Sullivan. Look how far we’ve come!

Grandmother Fish by Jonathan Tweet; illustrated by Karen Lewis

grandmother-fish

This book is similar to Sullivan’s book, but it adds a little more detail to the story and invites interaction from its audience. As major periods in our evolutionary lineage are reached, readers are asked to “wiggle” like our Grandmother Fish, “crawl” like our Grandmother Reptile, “squeak” like our Grandmother Mammal, “hoot” like our Grandmother Ape, and so on. As the story transitions from one main character to another, simplified versions of evolutionary trees are shown (like the one below).

grandmother-fish-2

A larger version of “Our Evolutionary Family Tree” is featured at the end of the story followed by several pages of additional information that adults can use to further explain evolution to children, including discussions on three major concepts of evolution (descent with modification, artificial selection, and natural selection), more details on the main characters in the book, and a guide to correcting common errors about evolution.

grandmother-fish-3

When Fish Got Feet, Sharks Got Teeth, and Bugs Began to Swarm by Hannah Bonner

when-fish-got-feet

This book is much more text heavy than the first two, but is still very approachable. The illustrations are both humorous and informative, and Bonner excels at explaining complex topics in a way that makes them easy to digest. Rather than covering hundreds of millions of years of evolution like the first two books, this book focuses mainly on events that occurred during the Silurian and Devonian periods – between 360 and 444 million years ago. It was during this time that plants were making their way to land and diverging into many different forms. Arthropods were doing the same. During this period, the earth’s atmosphere became more oxygen rich and soil began to accumulate largely due to the growth and expansion of land plants.

Recipe for a land plant from When Fish Got Feet by Hannah Bonner

Recipe for a land plant from When Fish Got Feet by Hannah Bonner

This was also a period of great diversification in the fish world. Jaws were becoming more common and skeletons made of bone (as opposed to cartilage) were developing.  The first tetrapods (fish with legs) emerged from the oceans and onto land in the Devonian period. These tetrapods were our early ancestors, and Bonner explains how some of the skeletal features that fish developed during this time period were precursors to our current skeleton.

Unlike the first two books, the evolution of plants receives some attention in Bonner’s book. It is during the Devonian period that the first trees and seed-bearing plants appear. As in the other books, there are additional resources at the end, including this important warning by Bonner: “Please remember that anyone can set up a Web site, so not everything you will encounter will be good science.”

A time line of life on earth from When Fish Got Feet by Hannah Bonner

A timeline of life on earth from When Fish Got Feet by Hannah Bonner

Key to helping children understand evolution is understanding it ourselves, and there are, of course, endless resources out there to help with this. I will suggest just two additional books. In keeping with the spirit of children’s books, there is a great illustrated biography of Charles Darwin (who is considered the Father of Evolution) called Darwin For Beginners by Jonathan Miller and Borin Van Loon. It’s basically Darwin’s life told in graphic novel form. And keeping with the fish theme, you can’t go wrong with Neil Shubin’s, Your Inner Fish, a fascinating look into the origins of many of the parts, pieces, and other features of the human body.

Do you have a favorite book, children’s or otherwise, about evolution? Please share it in the comment section below.

Advertisement
by

What Is a Plant, and Why Should I Care? part two

“Organisms green with chlorophyll appeared pretty early in Earth history, diversified, and adapted to oceanic, coastal, and finally terrestrial environments. As this took place, the Earth turned green.” – Joseph E. Armstrong, How the Earth Turned Green

world turned green

The Earth not only turned green, but the composition of its atmosphere dramatically shifted. Thanks in part to photosynthesis, Earth’s atmosphere went from having virtually no free oxygen to being composed of about 21% oxygen. The increasing availability of oxygen helped facilitate the evolution of more and more diverse forms of life. Had photosynthesis (specifically oxygen-producing photosynthesis) never come about, the Earth would not be anything like it is today.

There are organisms in at least three taxonomic kingdoms that have the ability to photosynthesize: Bacteria, Protista, and Plantae. A book itself could be written about how photosynthesis developed and how it differs among organisms. The important thing to note in a discussion about plants is that the type of photosynthesis that occurs in cyanobacteria is the same type that occurs in the chloroplasts of plants and green algae. Additionally, pigments called chlorophyll are only found in cyanobacteria and the chloroplasts of plants and green algae. As Joseph Armstrong puts it in How the Earth Turned Green, “evidence strongly supports the hypothesis that chloroplasts were free-living photosynthetic bacteria that became cellular slaves within a host cell.”

In Part One, we established that green algae are closely related to plants, and that a subset of green algae colonized the land and evolved into modern day plants. Plants are green because of cyanobacteria via green algae; however, cyanobacteria are not plants, and green algae may or may not be plants depending on your preference. Classification is not nearly as important as determining evolutionary relationships.

So, again, what is a plant? K. J. Willis and J. C. McElwain offer this summary in their book, The Evolution of Plants: “Plants are relatively simple organisms with a common list of basic needs (water, carbon dioxide, nitrogen, magnesium, phosphorous, potassium, some trace elements, plus various biochemical pathways necessary for photosynthesis). This list has remained almost unchanged from the first land plants to the present.” In Part One, we also listed three major features that all plants have in common: multicellularity, cell walls that contain cellulose, and the ability to photosynthesize.

Photosynthesis is a big one, because it means that plants make their own food. They are autotrophs/self-feeders/ producers. This sets them apart from heterotrophs, organisms that consume other organisms in order to obtain energy and other essential nutrients. Plants are at the bottom of the food chain, providing energy and nutrients to all other organisms that either directly or indirectly consume them. In Armstrong’s words:

“Eating and being eaten is a fact of life, a process by which the light energy captured by green organisms is passed through a series of consumers, a food chain, before eventually being lost as heat, which dissipates. Everything else is recycled with the able assistance of decomposers, primarily fungi and microorganisms, heterotrophs who obtain their food from dead organisms or their metabolic wastes. A large part of ecology concerns such trophic or feeding interactions, the energy transfers that result, and the cycling of biogeochemicals, the elements of life.”

Their ability to photosynthesize, among other things, gives plants a prominent role in the world’s ecosystems. Much more will be said about that as we continue, but first there are a few other things about plants worth mentioning.

Plants exhibit modular growth. While animals generally produce all of their body parts early on in life and rarely reproduce new body parts in replacement of lost ones, plants can continue to reproduce and replace body parts. Even at maturity, plants maintain embryonic tissues, which allows them to regenerate body parts as needed. This is one reason why so many plants can be propagated asexually via stem, root, and/or leaf cuttings. Roots can be encouraged to grow from unlikely places, and a whole new plant can be produced as a result.

Plants are generally stationary. Rooted in place, they must obtain everything necessary for life, growth, and reproduction by accessing whatever resources are in their immediate vicinity. Roots search the soil for water and other nutrients, and leaves harvest sunlight and carbon dioxide to make sugars. Relationships are maintained with soil fungi to aid in the search for water and nutrients, but otherwise, plants are largely on their own. Since they cannot run or hide, they must stand and fend for themselves when insects and other herbivores come to devour them. They have adapted a variety of chemical and physical defenses to address this.

Despite being largely immobile during their juvenile and adult phases, plants can actually be incredibly mobile during their embryonic stage (or in other words, as seeds/spores/progules). Employing biotic and abiotic resources, seeds and spores can potentially move miles away from their parent plants, enjoying a freedom of movement they will never know again once they put their roots down.

It is estimated that the total number of plant species on the earth today is around 400,000. (For reference, see this BGCI page and this Kew Gardens page. See The Plant List for up to date plant species names.) The first land plants evolved around 450 million years ago. It wasn’t until around 160 million years ago that the first flowering plants appeared, yet about 90% of the plants in existence today fall within this group. How many tens of thousands of species of plants have existed on Earth throughout history? I don’t think we can say. So many have come and gone, while others have radiated into new species. Exploring life that currently exists on this planet is an enormous pursuit on its own; add to that the exploration of life that once existed, and your pursuits become endless.

Sticky purple geranium (Geranium viscosissimum) one species of around species of extant flowering plants.

Sticky purple geranium (Geranium viscosissimum) is just one of more than 350,000 species of extant flowering plants.

At the close of the first chapter of his book, Armstrong highlights eight major historical events that have brought us plants as we know them today: “the origin of life itself, the development of chlorophyll and photosynthesis, the advent of the eukaryotic (nucleated) cell, the development of multicellular organisms, the invasion of land, the development of vascular tissues, the development of seeds, and the development of flowers.”  Consider that a brief synopsis of all we have to cover as we continue to tell the story of plants.

by

What Is a Plant, and Why Should I Care? part one

I want to tell the story of plants. In order to do that, I suppose I will need to research the 4 billion year history of life on earth. And so I am. Apart from satiating my own curiosity, studying and telling the story of plants advances me towards my goal of creating a series of botany lesson themed posts. Botany 101 and beyond, if you will. An ambitious project, perhaps, but what else am I going to do with my time?

So what is a plant anyway? We all know plants when we see them, but have you ever tried to define them? They are living beings, but they are not animals. They are stationary – rooted in the ground, usually. Most of them are green, but not all of them. They photosynthesize, which means they use water, carbon dioxide collected from the atmosphere, and energy harvested from the sun to make food for themselves. No animal can do that (okay…a few sort of can). They reproduce sexually, but many can also reproduce asexually. They are incredibly diverse. Some grow hundreds of feet into the air. Some barely reach more than a few centimeters off the ground at maturity. They have discernible parts and pieces, but they can also lose parts and pieces and then grow them back. There aren’t many animals that can do that. They have been on this planet for hundreds of millions of years, colonizing land millions of years before animals. Plants helped pave the way, and if it weren’t for plants, animals may not have stood a chance.

I don’t mean to pick on animals, it’s just that for a long time, humans grouped living things into just two kingdoms: Plantae and Animalia. Stationary things that appeared to be rooted to the ground or some other surface were classified as plants. Green things that lived in the water were also considered plants. Thus, lichens, fungi, algae, and everything we consider to be a plant today were placed in kingdom Plantae. Everything else was placed in kingdom Animalia. This, of course, was before much was known about microorganisms.

Dichotomous classification was reconsidered as we learned more about the diversity of organisms in each kingdom, particularly as the theory of evolution came into play and microscopes allowed us to observe single celled organisms and chromosomes. Eventually, fungi was awarded its own kingdom, which includes lichens – organisms composed of both fungi and photosynthetic species but classified according to their fungal components. Most of the algae was placed in a kingdom called Protista, a hodgepodge group of unicellular and unicellular-colonial organisms, some of which are animal-like and some of which are plant-like. Two kingdoms were also formed for prokaryotic organisms (organisms with cells that lack membrane bound organelles): Bacteria and Archaea.

Illustration of one current itteration of kingdom classification system (illustration credit: wikimedia commons)

Taxonomic kingdoms as we currently consider them (illustration credit: wikimedia commons)

In short, the answer to what is a plant seems to be whatever organisms humans decide to put in kingdom Plantae. One problem with this answer is that some chose to include certain species of algae and others don’t. But why is that? It has to do with how plants evolved and became photosynthetic in the first place.

Microorganisms developed the ability to photosynthesize around 3.5 billion years ago; however, the photosynthetic process that plants use today appeared much later – around 2.7 billion years ago. It evolved in an organism called cyanobacteria – a prokaryote. Eukaryotic organisms were formed when one single cell organism was taken inside another single cell organism, a process known as symbiogenesis. In this case, cyanobacteria was taken up and the eukaryotic organisms known today as algae were formed. The incorporated cyanobacteria became known as chloroplasts.

Not all algae species went on to evolve into plants. A group known as green algae appears to be the most closely related to plants, and a certain subset of green algae colonized the land and evolved into modern day plants (also known as land plants). That is why some taxonomists choose to include green algae in the plant kingdom, excluding all other types of algae.

Common stonewort (Chara vulgaris, a species of green algae (photo credit: www.eol.org)

Common stonewort, Chara vulgaris, a species of green algae (photo credit: www.eol.org)

The term land plants refers to liverworts, hornworts, mosses, ferns, fern allies, gymnosperms, and flowering plants – or in other words, all vascular and non-vascular plants. Another all encompassing term for this large group of organisms is embryophytes (embryo-producing plants).

Still confused about what a plant is? Three main features can be attributed to all plants: 1. They are multicellular organisms. 2. Their cell structure includes a cell wall composed of cellulose 3. They are capable of photosynthesis. Many species of green algae are unicellular, which is an argument for leaving them out of kingdom Plantae. Certain parasitic plants like toothwort, dodder, and beech drops have lost all or most of their chlorophyll and no longer photosynthesize, but they are still plants.

Deciding what is and isn’t a plant ultimately comes down to evolutionary history and common ancestry. As Joseph Armstrong writes in his book, How the Earth Turned Green, “Our classifications of human artifacts are totally arbitrary, but to be useful scientifically our classification of life must accurately reflect groupings that resulted from real historical events, common ancestries.”

Obviously this is going to be a multi-part series, so I will have much more to tell you about plants in part two, etc. For now, this You Tube video offers a decent summary.