Nick Lane – Life as we know it is chemically inevitable

Life as we know it, from its origins in deep-sea hydrothermal vents to the emergence of complex eukaryotic cells, appears to be a chemically inevitable outcome of fundamental thermodynamics, though complex life and intelligence remain rare bottlenecks.

• Basic life, with similar chemistry and metabolism to Earth's, is likely abundant across the universe due to chemical inevitability.

• The origin of complex life (eukaryotes) is a major, rare bottleneck, making advanced intelligence exceptionally scarce.

• Mitochondrial inheritance dictates the evolution of two sexes and their distinct reproductive strategies, ensuring genetic quality control.

Evolutionary biochemist Nick Lane explains that life's origins and its fundamental metabolic processes are chemically deterministic, likely occurring on any wet, rocky planet with similar conditions due to the efficiency of carbon and water chemistry. The major bottleneck for complex life and intelligence, however, is the singular event of eukaryote evolution through the acquisition of mitochondria, a highly improbable endosymbiosis that enabled larger genomes and multicellularity. This framework suggests that while basic life may be abundant, advanced life remains exceptionally rare.

The Rise of Eukaryotes

• 00:01:09 Eukaryotic cells, which constitute all large, complex life forms like plants and animals, are significant because they arose only once in Earth's 4-billion-year history, approximately 2 billion years ago. Despite bacteria and archaea possessing greater genetic versatility, they never developed the "trick" for complexity, which Nick Lane attributes to the acquisition of mitochondria. Mitochondria serve as powerful energy-generating units, providing the colossal energy potential needed for the evolution of large, complex cells and, eventually, multicellular organisms.

Origin of Life Theory

• 00:03:03 The prevailing theory for the origin of life proposes that early life forms emerged continuously with Earth's geochemistry in deep-sea hydrothermal vents, not in a 'primordial soup.' These vents, characterized by mineralized pores, created natural cell-like compartments with a proton gradient between acidic ocean waters and alkaline vent fluids. This gradient, along with catalytic metal-rich minerals (like iron and nickel sulfides) and available hydrogen and CO2, spontaneously drove the synthesis of life's fundamental building blocks, providing a continuous energy source and a concentrated environment for organic reactions.

Life's Chemical Inevitability

• 00:14:10 Fundamental chemistry dictates that carbon and water, being abundant elements, will predictably lead to similar metabolic processes and organic molecules on other wet, rocky planets. Carbon's ability to form strong, complex bonds, combined with ubiquitous water, hydrogen, and CO2, thermodynamically favors the production of essential molecules like Krebs cycle intermediates, fatty acids, amino acids, and nucleotides. This suggests that basic life, operating with similar chemiosmotic gradients and energy generation, is not contingent but chemically inevitable across the universe, with a substantial fraction of exoplanets likely harboring such life.

The Eukaryote Bottleneck

• 00:24:21 The evolution of eukaryotes represents a significant bottleneck for the emergence of complex, intelligent life. Despite the presumed abundance of simple life (prokaryotes) on countless planets, the successful endosymbiosis leading to eukaryotes is incredibly difficult and seemingly happened only once on Earth. Prokaryotes are constrained in size and complexity, often using extreme polyploidy to grow larger, which is metabolically expensive and does not lead to the sophisticated transport networks characteristic of eukaryotes. This implies that while the universe may be teeming with microbial life, complex multicellular organisms capable of intelligence could be exceedingly rare.

Origin of Sexes

• 00:43:06 The fundamental reason for two sexes, and the distinct characteristics of eggs and sperm, is linked to mitochondrial inheritance. The female sex universally passes on mitochondria, maintaining their genetic quality by minimizing mutations through careful preservation of oocytes. Males, conversely, do not pass on mitochondria, allowing them to mass-produce sperm with less genetic quality control and potentially faster growth rates, as regulated by the Y chromosome. This uniparental mitochondrial inheritance increases genetic variance in offspring, enabling natural selection to more effectively eliminate detrimental mutations.

Lateral Gene Transfer vs. Sex

• 00:56:52 Bacteria rely on lateral gene transfer (LGT) to adapt to changing environments, picking up small, random DNA fragments from their surroundings. This strategy allows them to maintain small, efficient genomes while accessing a vast 'pan-genome' of genes from other bacteria. In contrast, eukaryotes with their large genomes, made possible by mitochondria, cannot rely on LGT due to decreased efficiency with increased genome size. Instead, eukaryotes developed sexual recombination, a systematic and reciprocal process of exchanging entire genomes, which is crucial for maintaining genetic quality and complexity in larger, more unwieldy genomes.