Lecture 2: January 29

• Chapter 2 textbook.
• S. J. Gould, 1977. The child as man's real father. Chapter 7, in Ever Since Darwin, p. 63-69
• S. J. Gould, 1977. Size and Shape. Chapter 21, in Ever Since Darwin, p. 171-178

Web resources for this lecture:

From the web: on Haeckel's pictures:

• Description of Richardson's papers on faking of pictures by Haeckel
• d'Arcy Wentworth Thompson's look at allometry

How to sort fossils into morphological groups? Variations in size, shape, preservation, etc. Which one belong to one species? How to judge?

Species (see lecture 3):

• Biological species concept: group of individuals which interbreed. Can not be seen for fossils; is a problem for asexually reproducing organisms
• Morphological Species concept: organisms that look more like each other than like anything else (subjective)
• Typological species concept: all organisms that resemble a specific individual closely (specific individual, type, chosen by whom described the species). Basically, remnant from pre-Darwinian ideas about what a species is (see below).

Important to study variation within population. This is what makes the study of rare fossils so difficult. For example: human fossils are rare, and never are whole individuals preserved. Specimens found may have varied widely, main factors: age, sex. When we see fossils, how do we judge which specimens to put in the same 'species'? (i.e., morphological group); remember that with fossils we are always dealing with 'morphological species' (or morphospecies).

Variation within a species:

Plato: everything in the world is a vague shadow (shadow's on the wall of the cave) of the 'real' object. Thus everything is not really in its 'ideal' shape. Christianity: species were thoughts of God, created according to an ideal shape. Each species thus had its 'ideal shape', theoretical shape, never really reached in the real world. From Renaissance through to Darwin (and into today): type of the species (ideal form). Variability thus was seen as 'bad': deviation from an ideal shape (typological species concept).

Darwin: Natural selection: individuals compete, the ones who function better leave more offspring. Variability thus is an important component of living organisms, important factor in evolution (not 'bad'). Population concept of species: varying individuals make up a species.

Variation between individuals:

• Ontogenetic variation (during life span)
• Population variation (between individuals at same age).

Ontogeny (history of an organism from zygote to adult):

• Enormous variation possible (caterpillar-butterfly; tadpole-frog), especially early in life: one fertilized cell, develops into multi-cellular individual.

Linkages between ontogeny and phylogeny (development of an evolutionary lineage). Many organisms show evidence of ancestors in their early life stages. Haeckel: ontogeny recapitulates phylogeny. Human goes through 'fish-stage' (no real gills are present but a structure is present which is very similar to a strtucture in fish whch develops into the gills).

Haeckel's figures: recently much discussion that he falsified these, and strongly exaggerated the similarities between the various vertebrate groups (see web pages linked above). Embryos have features that are embryological (and thus have a function within the developing embryo), reveal nothing about evolution.

Most mammals: fairly gradual development. Many invertebrates: metamorphosis; e.g., larval stage free-swimming, adult fixed or slow-moving on bottom. Changes during growth: linked to what type of (if any) skeleton, exoskeleton (outside skeleton), endoskeleton (inside skeleton). Bones grow gradually, insects and lobsters molt in stages.

How to grow:

• Accretion: add layers (as in many molluscs, corals). Note: daily and annual growth rings in corals combined can be used to estimate the number of days in the year (thus rotation rate of the Earth); was larger in the deep past, because the Earth-Moon systen loses energy by tidal friction. Present theory on formation of Moon: Moon formed when large, Mars size asteroid hit Earth early on (about 4 billion years ago), its core was added to Earth, its mantle went on to form Moon. If you are interested, you can read more on the web on the Origin of the Planets and the Origin of the Moon; or watch a video-modeling of moon-forming from 'moonlets'.
• Addition of elements: foraminifera (chambers), Nautilus (chambers), Echinodermata (plates), Trilobites (segments)
• Molting: arthropods. Exoskeleton: hard outer skeleton can not grow; gets thrown off. Vulnerable when changing (soft stage). Limits size of arthropods (less so in water). Arthropods grow mainly during molting (discontinuously).
• Modification: change and add to skeleton (remodeling); typical for vertebrates.

Many organisms mix and match (e.g., Nautilus: accretion, than formation of septum and new chamber).

How to study growth in fossil specimens?

• Growth series (small to large specimens)
• Early stages preserved in adult specimen.

Ontogenetic growth: how do size and shape change, jointly?

• Transformation during growth (caterpillar model)
• Organisms do not change their proportions while growing (isometric growth)
• Organisms change their propoertions while growing (allometric growth)

Allometric growth is commonly necessary as a result of the requirements of increased size; allometric growth is the rule, isometric growth is very rare.

Principle of similitude: the mass of an organism increases by a power of 3, while its cross-sectional area increases by the power of 2, its length by power of one: as animals grow larger, their limbs most become more robust, rather than just being larger versions of those of smaller animals. Gallileo (1638). See also reading by Gould (Ch. 21)

Also: convoluted surfaces in lungs, intestines: need to increase surface area in large organisms.

Thermoregulation: surface areas with regard to volume. Small animals loose heat very quickly (large surface area for volume); small animals with fixed body temperature must eat the whole day. Big animals risk heat stress.

Group of interbreeding individuals; share gene pool.

Ecophenotypic variation: variation in morphology that is NOT genetic. Plants, corals. Bees: all individuals genetically the same. Size strongly influenced. Sex in crocodiles (not genetically determined)

Sexual dimorphism.: How to spot in fossils?

• Living relatives
• Male to female ratios: two types only.
• Time-space distribution.

Preservation modes: flattening, dissolution.