Starting my descent through The Descent of Man: Introduction

I have a number of goals for 2013. Several of them will play out here on the weblog, a few others will lead to publications. A handful have more speculative outcomes, and we'll see how they turn out.

One of my goals is to read and comment through the entirety of Darwin's The Descent of Man. That project I debut today.

I haven't done a similar close reading of the Origin, for several reasons. The Origin has something for every biologist but is read by startlingly few. Despite this deplorable lack of Darwin literacy, biologists read the Descent much, much less. So many historians of science and biologists have commented on the Origin that there remains little of value for me to add to its interpretation. By contrast Descent is uniquely interesting from an anthropological perspective.

I am not a historian and cannot track down all the sources that Darwin would have known or used. What I can do is to give some perspectives on our current understanding of human evolution, making clear in which ways Darwin was prescient and in which other ways he was plain wrong.

The main reason why I've undertaken the close reading is that Darwin was the first to seriously propose mechanisms for human evolution. He cared not only what had happened, but how it happened. Darwin was an intensely thoughtful analyst, and searched for evidence in every source at his disposal. Even so, he has only weak evidence about human prehistory and comparative primate anatomy and behavior. The mechanisms of genetics were not known at all, beyond the mere observation of inheritance of some traits. At the time of the Origin, only the Feldhofer Neandertal was suspected to represent any kind of prehuman ancestor or collateral.

More than half of the full work, The Descent of Man, and Selection in Relation to Sex, is about the mechanism of sexual selection, including evidence for the process across the animal kingdom. I am neither qualified nor especially concerned with the success of the sexual selection hypothesis for insects and birds. I am interested in the process for just the same reason Darwin included it in the Descent: because sexual selection may explain some aspects of human biology and variation. I will probably limit my close reading and commentary to the portions of the text that reflect directly upon primate and human evolution, which will leave out nearly half the full work.

I will be referring to the Project Gutenberg version of the 1871 text, which is freely available to readers in many formats. The text of Descent is public domain, allowing me to reprint it in its entirety, along with my notes.


The Introduction to the Descent is not the best place to start a close reading. It was finished too late in the process of writing, with Darwin having taken too great care and having used too solicitous a style in comparison to the rest of the work. Most important, the Introduction doesn't really present any arguments, just a summary of what will follow.

In other words, it's wimpy.

As I look at my notes on the Introduction, I see that my reactions are mostly about the connections to later material. My most salient reactions fall into two categories:

  1. Darwin's description of his own work in light of reception of the Origin, first published twelve years earlier.

  2. Darwin's allusions to the views of other scientists with whom, although agreeing on many general principles, he actually disagreed about many details and processes. Of particular interest are Charles Lyell, Alfred Russel Wallace, Thomas Huxley, and Ernst Haeckel.

In the Introduction to the work, Darwin emphasized the positive reviews of his earlier work, and de-emphasized his disagreement with earlier authors on human evolution.

The nature of the following work will be best understood by a brief account of how it came to be written. During many years I collected notes on the origin or descent of man, without any intention of publishing on the subject, but rather with the determination not to publish, as I thought that I should thus only add to the prejudices against my views. It seemed to me sufficient to indicate, in the first edition of my Origin of Species, that by this work light would be thrown on the origin of man and his history; and this implies that man must be included with other organic beings in any general conclusion respecting his manner of appearance on this earth. Now the case wears a wholly different aspect. When a naturalist like Carl Vogt ventures to say in his address as President of the National Institution of Geneva (1869), personne, en Europe au moins, nose plus soutenir la cration indpendante et de toutes pices, des espces, it is manifest that at least a large number of naturalists must admit that species are the modified descendants of other species; and this especially holds good with the younger and rising naturalists. The greater number accept the agency of natural selection; though some urge, whether with justice the future must decide, that I have greatly overrated its importance. Of the older and honoured chiefs in natural science, many unfortunately are still opposed to evolution in every form.

By waiting 12 years to write on human evolution, Darwin ceded ground to many other biologists, allowing them to write and promote theories about human origins before him. That decision had many drawbacks. But one central advantage is the authority that the intervening years and the acceptance of the Origin gave Darwin.

In consequence of the views now adopted by most naturalists, and which will ultimately, as in every other case, be followed by other men, I have been led to put together my notes, so as to see how far the general conclusions arrived at in my former works were applicable to man. This seemed all the more desirable as I had never deliberately applied these views to a species taken singly.

Is this really true? It certainly accords with the way anthropologists and biologists have divided up their subjects since Darwin. Evolutionary biologists study every kind of organism; anthropologists study the evolution of humans. Telling our story is special. But the following sentence is a great statement of why the human story must not be considered alone:

When we confine our attention to any one form, we are deprived of the weighty arguments derived from the nature of the affinities which connect together whole groups of organismstheir geographical distribution in past and present times, and their geological succession.

This is Darwin's defense of the comparative method. Restricting our field of view to a single lineage reduces our ability to understand the process of change. In this work, he will bring the geographical distribution in particular up to a level of substantiating relationships among organisms (humans and African apes, for example, to the exclusion of Asian apes) even where anatomical evidence was not compelling.

The homological structure, embryological development, and rudimentary organs of a species, whether it be man or any other animal, to which our attention may be directed, remain to be considered; but these great classes of facts afford, as it appears to me, ample and conclusive evidence in favour of the principle of gradual evolution. The strong support derived from the other arguments should, however, always be kept before the mind.
The sole object of this work is to consider, firstly, whether man, like every other species, is descended from some pre-existing form; secondly, the manner of his development; and thirdly, the value of the differences between the so-called races of man. As I shall confine myself to these points, it will not be necessary to describe in detail the differences between the several racesan enormous subject which has been fully discussed in many valuable works.

This is an interesting passage. My impression has always been that Darwin had a distaste for the work of contemporaries who studied human races. It is also an area where his disagreement with Wallace was the greatest. The Descent itself includes a great deal about race, but does not consist of description. This passage may have insulated him from criticism that his work did not have the description of skulls that had recently been published by J. Barnard Davis ("J. Barnard Davis and the variation within races") or some earlier scholars.

The high antiquity of man has recently been demonstrated by the labours of a host of eminent men, beginning with M. Boucher de Perthes; and this is the indispensable basis for understanding his origin. I shall, therefore, take this conclusion for granted, and may refer my readers to the admirable treatises of Sir Charles Lyell, Sir John Lubbock, and others. Nor shall I have occasion to do more than to allude to the amount of difference between man and the anthropomorphous apes; for Prof. Huxley, in the opinion of most competent judges, has conclusively shewn that in every single visible character man differs less from the higher apes than these do from the lower members of the same order of Primates.
This work contains hardly any original facts in regard to man; but as the conclusions at which I arrived, after drawing up a rough draft, appeared to me interesting, I thought that they might interest others.

Characteristic understatement, in this case to the point of falsehood. Descent is chock-full of ideas that never appeared elsewhere. Where Darwin had famously left the subject of human evolution to the briefest statement in the Origin ("Light will be shed on man and his origins"), other authors in the intervening twelve years picked up the slack. Yet Darwin did have extensive notes on his ideas about human origins, and corresponded extensively with authors who published their ideas during the 1860s. The most interesting of those letters are to and from Wallace, as I'll note throughout.

It has often and confidently been asserted, that mans origin can never be known: but ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science. The conclusion that man is the co-descendant with other species of some ancient, lower, and extinct form, is not in any degree new. Lamarck long ago came to this conclusion, which has lately been maintained by several eminent naturalists and philosophers; for instance by Wallace, Huxley, Lyell, Vogt, Lubbock, Bchner, Rolle, &c., and especially by Hckel. This last naturalist, besides his great work, 'Generelle Morphologie (1866), has recently (1868, with a second edit. in 1870), published his Natrliche Schpfungsgeschichte, in which he fully discusses the genealogy of man.

Haeckel's book was a highly popular, accessible German description of Darwinian theory and the history of life. It was later translated into English as The History of Creation, a translation that was edited by the prominent biologist E. Ray Lankester, but did not appear until 1874.

If this work had appeared before my essay had been written, I should probably never have completed it. Almost all the conclusions at which I have arrived I find confirmed by this naturalist, whose knowledge on many points is much fuller than mine. Wherever I have added any fact or view from Prof. Hckels writings, I give his authority in the text, other statements I leave as they originally stood in my manuscript, occasionally giving in the foot-notes references to his works, as a confirmation of the more doubtful or interesting points.

Haeckel's "full discussion of the genealogy of man" was organized into more than 22 stages, going all the way back to bacteria. It's really not very much like Darwin's Descent. Haeckel also devoted a chapter to describing theories about the migration and diversification of human races, and this shares more subject matter with Darwin's account, but is really quite brief compared to the corresponding portions of the Descent. All in all, it was generous of Darwin to point so prominently to Haeckel's book, which was already widely known in England, but as I'll describe further in later installments there was little chance of confusing Descent for Haeckel's work.

During many years it has seemed to me highly probable that sexual selection has played an important part in differentiating the races of man; but in my Origin of Species (first edition, p. 199) I contented myself by merely alluding to this belief. When I came to apply this view to man, I found it indispensable to treat the whole subject in full detail. Consequently the second part of the present work, treating of sexual selection, has extended to an inordinate length, compared with the first part; but this could not be avoided.

Darwin lays out the theory of sexual selection with many varied and detailed examples, as was his special talent. Any editor today would have taken most of this material out of the book and put it in a separate book. I do not plan to treat these chapters in detail during my reading, except for those bearing specifically upon primates and humans. Darwin's motivation behind this part of the work was telegraphed in a letter to Wallace in 1864:

Secondly I suspect that a sort of sexual selection has been the most powerful means of changing the races of man. I can shew that the difft races have a widely difft standard of beauty. Among savages the most powerful men will have the pick of the women & they will generally leave the most descendants.

Wallace disagreed with Darwin on this point, and generally maintained that sexual selection was not powerful enough in humans to have affected human variation. The Wallace-Darwin disagreement on the power of selection was far-reaching. The two men clearly understood that their respective opinions had consequences across biology. But more on that point later.

Returning to the Introduction:

I had intended adding to the present volumes an essay on the expression of the various emotions by man and the lower animals. My attention was called to this subject many years ago by Sir Charles Bells admirable work. This illustrious anatomist maintains that man is endowed with certain muscles solely for the sake of expressing his emotions. As this view is obviously opposed to the belief that man is descended from some other and lower form, it was necessary for me to consider it. I likewise wished to ascertain how far the emotions are expressed in the same manner by the different races of man. But owing to the length of the present work, I have thought it better to reserve my essay, which is partially completed, for separate publication.

The Expression of Emotions is itself a remarkable piece of work. It establishes an evolutionary theory of behavior, providing connections between behavior and anatomy in a way that would echo through the work of later ethologists.

OK, that's the Introduction. I've added quite enough here, and have probably gone on too long on some points without adding references. I want to get this up and get started on the meaty part of the text, which are not so much about Darwin's intentions and are devoted instead to statements of fact and theory.

Next, we get right into Darwin's argument for the body structure of humans as evidence for evolution.