The human infant intestinal microbiota develops rapidly after birth, transitioning from sterility to a complex microbial ecosystem that becomes increasingly similar to that of adults over the first year of life. This study used a microarray to analyze the microbial communities in stool samples from 14 healthy, full-term infants, including a pair of fraternal twins, collected at regular intervals from birth to one year. The microbial communities varied significantly between infants, but by the end of the first year, they had converged toward a profile characteristic of the adult gastrointestinal tract. The microbial composition and temporal patterns of the twins were strikingly similar, suggesting that environmental factors play a major role in shaping the microbial community. The study also analyzed samples from mothers, fathers, and siblings to investigate the origins of the infant microbiota. The results showed that the microbial communities of infants were influenced by factors such as mode of delivery, diet, and exposure to maternal microbiota. The study found that Bifidobacteria were not always dominant in the infant microbiota, contradicting previous assumptions. The microbial communities of infants were also influenced by the presence of fungi and archaea, which were detected in some samples. The study highlights the importance of understanding the development of the infant microbiota and its role in health and disease. The results suggest that the microbial communities of infants are highly variable, but they eventually converge toward a profile similar to that of adults. The study provides a detailed reference for future research on the factors that influence the development of the infant microbiota.The human infant intestinal microbiota develops rapidly after birth, transitioning from sterility to a complex microbial ecosystem that becomes increasingly similar to that of adults over the first year of life. This study used a microarray to analyze the microbial communities in stool samples from 14 healthy, full-term infants, including a pair of fraternal twins, collected at regular intervals from birth to one year. The microbial communities varied significantly between infants, but by the end of the first year, they had converged toward a profile characteristic of the adult gastrointestinal tract. The microbial composition and temporal patterns of the twins were strikingly similar, suggesting that environmental factors play a major role in shaping the microbial community. The study also analyzed samples from mothers, fathers, and siblings to investigate the origins of the infant microbiota. The results showed that the microbial communities of infants were influenced by factors such as mode of delivery, diet, and exposure to maternal microbiota. The study found that Bifidobacteria were not always dominant in the infant microbiota, contradicting previous assumptions. The microbial communities of infants were also influenced by the presence of fungi and archaea, which were detected in some samples. The study highlights the importance of understanding the development of the infant microbiota and its role in health and disease. The results suggest that the microbial communities of infants are highly variable, but they eventually converge toward a profile similar to that of adults. The study provides a detailed reference for future research on the factors that influence the development of the infant microbiota.