Aristotle had the notion that organisms could be placed on a linear natural scale according to complexity of structure and function, such that higher organisms showed greater vitality and ability to move. Evolution has done something similar, building up the ladder of life from very basic micro-organisms and then scaling up to greater integrative complexity. In that sense, living things are concatenations and elaborations of earlier solutions, which have been tweaked through natural selection, refinements being added to the code, often making it a bit longer.
Yesterday a large concatenation of more than 25 authors (did they write a paragraph each?) has published in Nature “Comparative analysis of the transcriptome across distant species” and studied the overlap between humans, worms and flies.
They conclude: Overall, our comparison of the transcriptomes of three phylogenetically distant metazoans highlights fundamental features of transcription conserved across animal phyla. First, there are ancient co-expression modules across organisms, many of which are enriched for developmentally important hourglass genes. These conserved modules have highly coordinated intra-organism expression during the phylotypic stage, but display diversified expression before and after. The expression clustering also aligns developmental stages between worm and fly, revealing shared expression programs between embryogenesis and metamorphosis. Finally, we were able to build a single model that could predict transcription in all three organisms from upstream histone marks using a single set of parameters for both protein-coding genes and non-coding RNAs. Overall, our results underscore the importance of comparing divergent model organisms to human to highlight conserved biological principles (and disentangle them from lineage-specific adaptations).
What has this got to do with our usual subject, intelligence? Well, Heitor Fernandes, Michael A.Woodley and Jan te Nijenhuis have been investigating whether there is a Great Chain of Being Intelligent. Could the same forces that created ancient co-expression modules have done so for the nervous system? Indeed, how could they not have done so? Evolution happens because organisms survive for long enough and in one piece so as to mature and reproduce. They cannot toss forwards only those genes which will conform to refined sensibilities generations later. Do all animals, like humans, have a general intelligence factor accounting for half of their abilities?
As you would expect from these three clever monkeys, the paper is rich with content and deploys some complex statistics. I do not consider myself to be a religious fundamentalist, but this gang even attack principal components analysis. How does one deal with such iconoclasts, who seem bent on replacing the ancient verity with Principal Axis Analysis (see their apostasy below).
Anyway, our three monkeys have respected some traditions in that they evaluate animal intelligence in terms of a Five Factor model of primate IQ: Innovation, tool use, social learning, tactical deception and extractive foraging.
This is what they say:
General intelligence has been shown to exist within and among species of mammals and birds. An important question concerns whether it is the principal source of differences in cognitive abilities between species, as is the case with comparisons involving many human populations. Using meta-analytic databases of ethological observations of cognitive abilities involving 69 primate species, we found that cognitive abilities that load more strongly on a common factor (which is here termed G, in line with the terminology developed in previous literature to describe aggregated measures of general intelligence) are associated with significantly bigger interspecies differences and bigger interspecies variance. Additionally, two novel evolutionary predictions were made: more G-loaded abilities would present (1) weaker phylogenetic signals, indicating less phylogenetic conservativeness, and (2) faster rates of trait evolution, as it was hypothesized that G has been subjected to stronger selection pressures than narrower, more domain-specific abilities. These predictions were corroborated with phylogenetic comparative methods, with stronger effects among catarrhines (apes and Old World monkeys) than within the entire primate order. These data strongly suggest that G is the principal locus of selection in the macroevolution of primate intelligence. Implications for the understanding of population differences in cognitive abilities among human populations and for the theory of massive modularity applied to intelligence are discussed.
We obtained meta-analytical frequency-count data on five cognitive abilities from a total of 69 primate species. Data on four different cognitive abilities were obtained directly from Reader et al. (2011). Their meta-analytic database was produced by examining over 4000 articles published from 1925 to 2000 for reports of behaviors indicative of intelligence (described above) in extant primate species. Data on a fifth cognitive ability were obtained from a meta-analytic compilation produced by Byrne and Whiten (1990), and originally obtained by surveying the large memberships of the International Primatological Society, the Primate Society of Great Britain, the Association for the Study of Animal Behavior, the Animal Behavior Society, and the American Primatological Society combined.
Different species use complex problem-solving behaviors in different ecologies, thus the various senses (e.g., olfaction, hearing) have different weights of importance for different species with regard to how they perceive and identify ecological and social problems to be tackled, the motivation systems, dependence on rewards, and tolerance to frustration vary across species, thus it is extremely difficult to calibrate experimental conditions to the ecological idiosyncrasies of each species.
Additionally, experimental cognitive tests are not available for large numbers of species or on a sufficiently broad range of cognitive abilities. Hence the natural frequency-counts approach used in the collection of the current dataset is the most
appropriate and ecologically valid estimate of intelligence for comparative studies, that is, studies in which macro evolutionary predictions are being tested at the cross-species level (Reader & Laland, 2002; Reader et al., 2011; see also Lefebvre, 2011).
We conducted a Principal Axis Factor analysis (which, contrary to principal components analysis, controls for error variance; Costello & Osborne, 2005) to test the factor structure of the five cognitive abilities. We also tested their factor structure with Unit Weighted Factoring (UWF), which avoids the well-known sample-specificity of factor-scoring coefficients produced by standard errors of inconsistent magnitudes in small samples (Gorsuch, 1983). Both factor analyses were conducted after residualizing each cognitive ability against research effort so as to avoid publication bias.
The findings reported here have substantial implications. Firstly, the species differences in intelligence and their variance from the mean are biggest on the more G-loaded cognitive abilities, as is also the case for population differences within the
human species. This suggests that the evolutionary accounts developed to explain population cognitive differences in humans are plausible, as it is improbable that a “Factor X” (the term generally used to refer to putative environmental
causes of population differences in cognitive abilities; Jensen, 1973) could be operating to create the findings reported here among primate species. Several putative “Factor Xs” involve systematic negative discrimination or stereotype threat
(Sesardic, 2005). It is difficult to envisage how these social forces might extend across primate phylogenies. A more parsimonious account of the apparent ubiquity of validation for Spearman's hypothesis is that it results from more common-factor-loaded abilities simply being more revealing of taxonomic group differences owing to differential selection having operated historically on general intelligence to a greater extent than on narrower and more modular abilities — and that this is likely the same for human populations as it is for primate species, the principal difference being the duration of selection.
Comment: it looks as if a G factor (principal axis based on aggregated measures) can be extracted from primates, even though they cannot be tested with pencil and paper and spoken vocabulary definitions. Primates appear to conform to the same general intellectual factor g (based on individual measures) which underlies human abilities.
Darwin should have the last word (1871, p. 105)
“the difference in mind between man and the higher animals… is certainly one of degree and not of kind" (Italics added for emphasis).