Final answer:
The primary source of data for phylogenetic reconstruction is a combination of morphological and molecular data, including analysis of DNA. Cladistics and computational methods assist in constructing phylogenetic trees, which are continually updated as new data emerge.
Step-by-step explanation:
The primary source of data used in phylogenetic reconstruction to determine evolutionary relationships among species is a combination of morphological and molecular data. Scientists analyze structural features, developmental patterns, fossil records, and genetic information to ascertain homologous characteristics, which indicate common ancestry. They employ methods such as cladistics, which organizes species based on shared derived characters, and rely on computer programs to handle complex data to construct evolutionary trees or cladograms.
While morphological information and the fossil record provide historical context, it is the molecular data, particularly DNA analysis, that has significantly advanced the field. This genetic information helps identify homologous genes and distinguish them from analogous features, which result from convergent evolution rather than common ancestry. The resulting phylogenetic trees are hypotheses and continually revised with new data and insights, making them dynamic depictions of evolutionary history.