What People Are Saying About this Book

Below are just a few of the comments received regarding Rhythms of Life. I would be happy to receive yours as well.


Thurs, 7 Jan 2010 From: Robert Clipperton, Saskatchewan
Hi Susan,
...I might add that I really enjoyed reading your book and my copy was become quite dog-eared from having been passed around to various friends and acquaintances.  Personally, I don't know what could be more interesting than dwarf elephants, giant rodents and dog evolution.


Tue, 14 Mar 2006 From: BC
Hi Susan,
Just wanted to tell you how much I enjoyed reading your book. First, it is so well-written! Thank you for that. And, second, it is so interesting and stimulating. My brain was whirling. You have proposed answers to questions that your typical gene-centred, Darwinian explanations have either avoided or couldn't answer! I am so impressed. Well done. I expect it will generate much discussion and controversy. Anyway, congratulations.

Sun, 12 Mar 2006 From: JJ
Dear Susan,
Your beautiful book arrived on Friday! I started reading right away and I love it! Both style and content are excellent, very exciting, very well-researched, very thorough and I'm learning lots of new things as well. I'm so proud of you! You have made me very happy, it's a joy to read and that's what I'm going to do right now.

Sun, 9 Apr 2006 A newspaper review
*Thyroid theory updates Darwin*

An article by: BRADLEY J. FIKES - Staff Writer
Front page of the Science and Technology Section, North County Times,
a daily newpaper serving San Diego, CA, USA

"One of the most perplexing gaps in evolutionary theory is the lack of a precise explanation of what happens when a species forms. Susan J. Crockford, an evolutionary biologist with a doctorate in zoology, proposes an ambitious theory to explain speciation in vertebrates: It's driven by thyroid hormones.

Crockford has written about this theory in various research papers, and has just published a book setting forth her ideas: "Rhythms of Life: Thyroid Hormone and the Origin of Species" (www.rhythmsoflife.ca/). Each species has its own "rhythm" of thyroid hormone production, she contends. Changes in this rhythm produce differences in behavior, appearance and reproductive habits that help isolate a new species from its progenitor.

It's an audacious claim to make, but Crockford makes a plausible case. The key thyroid hormones, thyroxine and triiodothyronine, control growth and metabolism and take part in the stress response. So they are good candidates for such an overarching control mechanism….

…Crockford says her theory helps explain problems in diagnosing thyroid-related human health problems. Since variation is a normal part of any population, modern humans will have their own individual thyroid rhythms, a subset of the species rhythm. This implies that a one-size-fits-all medical test for thyroid function will miss people whose individual metabolism and biochemistry requires higher than "normal" levels of thyroid hormones.

Weight loss and depression, two symptoms of hypothyroidism (insufficient thyroid function), are easily misinterpreted, she writes. That's especially significant for women because women are much more likely than men to have hypothyroidism.

The book also is filled with fascinating facts:
- Thyroxine is found in all vertebrates, implying that it's a very basic part of biochemistry.
- The digestive tract absorbs thyroxine intact, so animals (or humans) can get thyroxine from uncooked meat or raw egg yolks.
- Thyroxine deficiency may aggravate symptoms of menopause.

Whether or not Crockford succeeds in establishing her theory, she has succeeded in writing an entertaining, fact-filled book about evolution that stands out for its originality."

Contact staff writer Bradley J. Fikes at (760) 739-6641 or bfikes@nctimes.com.


Fri. 22 Sept. 2006 From: LC, via contact us page
I couldn't put this important book down. It is a fascinating, ground breaking exposition that pushes the understanding of evolution to a new level. It is clearly written and an absorbing feast for the mind.

After Darwin, a myriad of questions, anomolies & puzzles lingered. Susan Crockford's theories give new insight from a wide range of disciplines.

Obtain for yourself a first edition! It will become a family heirloom. There are few things more exciting than a new way to see the world. Here it is.


Fri. 22 Sept. 2006 A note from Ernst Mayr, 2003
(see the Photo Gallery for a copy of the letter (and the transcript of the handwritting) from prominent evolutionary biologist Ernst Mayr, which he wrote after reading some of my published papers on this topic, less than two years before he died).