The Signature of All Things is a sweeping generational novel by writer Elizabeth Gilbert. In this novel, Alma Whittaker is the unattractive daughter of an adventurous botanist who had set out to be better than his father before him. Alma has inherited her father’s love of botany, but lacks his sense of adventure. Alma spends most of her life in seclusion on the family estate, unmarried and alone. However, after a brief, unsatisfying marriage to a gifted artist, Alma sets out into the world in an attempt to understand her husband. In time, Alma has an epiphany about the fight for survival seen in all things, from mosses to human beings; but, she misses her chance for fame when another scientist publishes the same theories before her. The Signature of All Things is a novel of self-discovery that takes the main character and the reader on a journey that will leave their lives forever altered.

Alma Whittaker is the only biological child of Henry and Beatrix Whittaker. Alma’s father, an uneducated botanist who built his wealth with pharmaceutical plants, is an adventurous man who teaches Alma that there are no limits to life with the right amount of ambition. As Alma grows, she becomes highly educated, developing a love in botany that will shape her entire life.

Alma has a quiet childhood that is altered when her parents adopt the young girl of a gardener and his promiscuous wife. Alma resents her new sister, Prudence, because she is beautiful. Alma finds Prudence to be less intelligent and does not spend much time in sisterly behaviors. However, when a new neighbor named Retta moves in next door and makes herself a friend of the two girls, Alma finds that Prudence is more forthcoming around Retta and easier to get along with.

When the girls are in their late teens, a local botany publisher, George Hawkes, begins coming to the house often. George even begins publishing some of Alma’s articles on plants. Alma begins to imagine she is in love with George and that he might return her feelings. For years Alma harbors these feelings, sharing them only with Prudence in rare moments of sisterly confidence. One day Retta tells Alma that she is getting married, and Alma is shocked to learn Retta's fiancé is George. When Alma tells Prudence this news, Prudence shows uncharacteristic anger toward Alma.

Both Retta and Prudence marry within a short time of one another. Alma is shattered by this because she is afraid she is destined to never be married. Instead, Alma focuses on her beloved plants and decides to make a study of mosses. For the next twenty years, Alma studies mosses and publishes two books on them. At the same time, Prudence raises a family with her teacher husband. George and Retta suffer in a loveless marriage. When Retta becomes a danger to herself, Alma helps George place her in a mental hospital.

When Alma is in her early fifties, George shows her exquisite lithographs done by a new artist named Ambrose Pike. Alma is so impressed with the lithographs, she invites Ambrose to visit her home, White Acre. Ambrose comes, and they hit it off immediately. One night, after Ambrose has told Alma his belief that he is meant to live on a higher plane, Ambrose catches her reading obscure books in an attempt to understand him. Ambrose invites Alma into a private place where he tries to communicate with her without words. Alma feels as though they did communicate and that Ambrose had fallen in love with her. Therefore, when Ambrose asks to marry her a short time later, Alma is more than thrilled to accept.

Alma and Ambrose are married in a short time. However, Alma is shocked when Ambrose refuses to be intimate with her. Alma tries to push the issue only to learn that Ambrose does not want a physical relationship with her. Alma has Ambrose moved into another bedroom and eventually sends him to Tahiti to oversee a vanilla plantation her family owns there. Little more than a three years later, Alma gets word that Ambrose has died.

After Ambrose’s death, Alma is given his valise and finds within it multiple drawings Ambrose did of a young black man. Alma realizes that her husband was a homosexual, which explains why he did not want a physical relationship with her. However, she now wonders what this other man had that made Ambrose love him. Therefore, after Alma’s father dies, she decides to go to Tahiti and find this man.

Alma has never traveled before and finds Tahiti to be strange and scary. However, she eventually succeeds in finding Ambrose’s lover. They speak about Ambrose, and Alma feels as though she has finally found some of the answers she has always wanted. At the same time, she comes to an understanding of the fighting nature of the world, of the need for all living organisms to fight the weaker in order to survive. Alma writes a paper about this survival instinct as she travels to Holland.

In Holland, Alma goes to her uncle who is the director of the Hortus Botanicus in Amsterdam. Alma leaves with him her thesis and a request for a job. Alma’s uncle loves her paper and immediately welcomes her into his life and his home, giving her a job as Curator of Mosses. Alma and her uncle fight repeatedly about her refusal to publish her paper. Alma feels the paper is not complete because she cannot explain why some organisms sacrifice themselves for stronger ones, such as a stranger who drowns to save a drowning child.

Shortly after her uncle’s death, Charles Darwin publishes On the Origin of Species. Alma is shocked to find that it is her theory, only better written. Alma also learns that there was another scientist, Alfred Russel Wallace, who also wrote on the same theory. Alma feels close to these two other scientists and follows their careers closely. After Darwin dies, Alma is growing quite old and feeble. She invites Wallace to speak at the Hortus Botanicus. Alma shows Wallace her paper and feels a strong kinship to him that makes her feel less alone. Alma is then content with her life and ready to die.