The Elements of Evolution (32-1) Jean-Baptiste Lamarck

 Jean-Baptiste Lamarck

Behaviour may drive evolutionary diversification. ~ Spanish evolutionary biologist Oriol Lapiedra

French naturalist Jean-Baptiste Lamarck (1744–1829) considered evolution to be adaptive. His book Zoological Philosophy was published in 1809, the year Darwin was born.

Lamarck proposed 2 axioms of evolution. The 1st was about adaptation based upon biological need, and its corollary: depreciation by disuse.

In every animal, more frequent and sustained use of an organ strengthens that organ, while the constant disuse of an organ imperceptibly weakens it and ends in its disappearance. ~ Jean-Baptiste Lamarck

Lamarck cited the long neck of the giraffe as an example of usage – stretching to reach leaves – driving adaptation. 2 centuries later, this proved true.

The most primitive giraffe already started off with a slightly elongated neck. The lengthening started before the giraffe family was even created, 16 million years ago. ~ American zoologist Melinda Danowitz in 2015

Lamarck’s 2nd axiom was that the lifestyles of parents affected their offspring.

Everything that Nature has caused individuals to acquire or lose by the influence of the circumstances, it preserves by heredity and passes on to the new individuals descended from it. ~ Jean-Baptiste Lamarck

In the 1950s, after geneticists discovered DNA, they thought that they had unlocked the secret of inheritance. The recipes of life were encoded in DNA; simple as that.

With that in mind, Larmarck’s hypotheses became moribund. It was not until the end of the 20th century, with the discovery of epigenetics, that Lamarck’s prescient 2nd axiom, on heritable variation, was vindicated.

The possibility that acquired (epigenetic) ‘marks’ can be passed from parents to children has a deliciously Lamarckian flavour that has proved difficult to resist as a potential antidote to genetic determinism. ~ English geneticist Adrian Bird

Roundworms develop resistance to a virus and can pass that immunity onto to their progeny: an acquired trait conferred for many consecutive generations. No genetic mutation is involved.

The immunity is transferred in the form of small viral-silencing agents called viRNAs, working independently of the organism’s genome. ~ Israeli neurobiologist Oded Rechavi

RNA interference (RNAi) is a process that cells use to silence specific genetic expressions. It is commonly employed to fight off viruses and other genomic parasites. RNAi waylays messenger RNA (mRNA), a courier for gene expression. Without mRNA in the act, a gene is left inactive.

What works for worms works all the way up the evolutionary ladder. Epigenetic mechanisms let animals and their offspring evolve while maintaining the same genetic pedigree. This flexibility, coupled to gene conservation, is a great advantage in adaptability, both in uptake and in rapid reversibility.

Around the world, several fish species evolved in caves, without sunlight, all sharing common adaptations, including eye loss, enhanced senses on their skin to assist in navigation, and loss of skin pigment. Disuse has an evolutionary effect owing to a natural tendency to conserve resources.

Animals’ biorhythmic clocks typically rely upon sunlight for calibration. Cave fish lack the Sun’s cue. The circadian clock is a highly conserved physiological timing mechanism, as many bodily functions are synchronized to the internal clock. A cave fish’s clock is set by its feeding schedule.

Taste sensitivity depends upon diet. As meat mostly stimulates the umami taste receptors, carnivorous mammals are overly sensitive to that particular taste, but lose their ability to savor sweetness, as it confers no benefit. In contrast, the giant panda, which feeds primarily on bamboo, lacks a functional umami taste receptor.

Raccoons and bears eat a lot of meat, but their diets are fairly broad. They retain the genes to taste sweetness.

Sea lions and dolphins descended from land mammals, returning to aquatic environs 35 and 50 million years ago, respectively. Adaptive to their diets, these animals experienced atrophies in their taste systems.

Conversely, where specific senses dominate, they become especially acute. Sometimes such adaptations are a matter of both sensory sensitivity and behavior. Rats rely heavily upon their sense of smell: so much so that they can target their sniffing to specific objects of interest.

When a bird changes from terrestrial foraging to finding food in the trees adaptations accelerate in certain physical characteristics. A bird adopting an arboreal lifestyle grows shorter hindlimb bones and longer tails, providing a perching improvement.

10 MYA a more arid climate caused East Africa to change from woodland to grassland. The elephants there switched from browsing to grazing by 8 MYA, when the terrain was still a mosaic of vegetation. Within 3 million years, elephant teeth had evolved to better accommodate the shift in dietary preference. Elephant behavior shaped morphological adaptation.

A female dolphin in western Australia started protecting her sensitive rostrum from damage when foraging on the seabed by covering it with a protective sponge. Others in the pod learned it, and it was taught to offspring. This cultural knowledge, passed on for generations, took genetic expression.

A socially transmitted behaviour like tool use can lead to different genetic characteristics within an animal population. ~ Swiss evolutionary geneticist Anna Kopps

As de novo protein synthesis is required for memory formation, memories are epigenetically encoded. These gene expression programs are readily transmitted to offspring. This is the molecular facet of precocious knowledge evolving.

(Material substrates, such as nuclei acids and associated chemical compounds, are ever only coincidental, not causal, to the energetics by which Nature is emergently composed.)

Epigenetic processes play a role in memory consolidation and help to transmit acquired memories even across generations in a Lamarckian manner. ~ German molecular biologist André Fischer